IGS Symposium 2010 on Earth's Disappearing Ice — Abstracts

Comparing the sensitivities of low-order ice sheet models to changes in model parameters
Patrick J. Applegate, Nina Kirchner, Emma J. Stone, Ralf Greve
Corresponding author: Patrick J. Applegate — patrick.applegate@natgeo.su.se
In this work, we compare the sensitivities of two numerical models of the Greenland ice sheet to changes in the models' input parameters. Ice sheet models help us assess the risk of sea level rise associated with increased mass loss from Greenland; however, the behavior of these models is not completely characterized. The EISMINT intercomparison exercises benchmarked the ice flow modules of ice sheet models against analytical solutions, and established differences between the transient behavior of ice sheet models for paleo- and future forcings. However, these intercomparison projects assumed constant values of several input parameters that are somewhat uncertain. Thus, more work is needed to determine how models of the Greenland ice sheet respond to changes in their input parameters.

Recent work by EJS and colleagues (Stone et al., in review, The Cryosphere) establishes methods for assessing the sensitivities of ice sheet models. They used Latin hypercube sampling to evaluate the equilibrium ice sheet volume, area, and maximum thickness for the Glimmer-CISM ice sheet model as a function of five input parameters. These parameters were the atmospheric lapse rate, the flow enhancement factor, the geothermal heat flux, and the positive degree-day factors for ice and snow.

Building on this groundbreaking work, we have performed the same analysis with the SICOPOLIS ice sheet model. We report on the similarities and differences between the behavior of the two models.

We anticipate that this work will benefit the community in several ways. First, these sensitivity analyses are a necessary step in tuning ice sheet models to reproduce both modern and ancient ice sheet geometries. Second, this work provides a baseline for evaluating recent improvements in ice sheet models. Higher-order models should yield a wider range of equilibrium ice volumes than the zeroth-order shallow-ice approximation models that we investigate here. This hypothesis deserves testing. Last, it may be possible to develop perfect model experiments based on this work that will inform future field measurement campaigns.
West Greenland Outlet Glacier Sensitivity (2000-2009)
Ellyn M. McFadden, Ian M. Howat, Yushin Ahn, Ian R. Joughin, Ben E. Smith, Wieslaw Maslowski
Corresponding author: Ellyn M. McFadden — ellyn.mcfadden@gmail.com
Rapid changes in the dynamics of Greenland’s marine-terminating outlet glaciers within the past decade indicate a complex response of these systems to recent climatic forcing. Widespread accelerations in glacier flow-speed along Greenland’s southeast coast have been linked to retreat of glacier fronts correlated with anomalously warm ocean temperatures. Following periods of retreat, many glaciers slowed, thickened, and advanced, indicating dynamic changes in glacier behavior on inter-annual time scales. Despite regional ice thinning and retreat, current data suggest that glaciers of Greenland’s west coast have not undergone substantial acceleration comparable to that of southeastern glaciers. To investigate the potential controls behind this contrasting behavior, we derive time series of front position, surface elevation, and surface slope for 59 marine-terminating outlet glaciers in west Greenland from 2000-2009. RADARSAT, ASTER, Landsat, and SPIRIT images, combined with NASA ATM data, are used to construct nearly-annual time series of glacier change to resolve short-term (annual) and long-term (decadal) changes in glacier dynamics in response to climate forcing. Resultant time series are compared to regional air and ocean temperature data to constrain climate forcing conditions. Changes in front position and surface elevation were asynchronous on annual time scales but synchronous on decadal time scales, with 50 of 59 glaciers retreating and up to ~120 m of thinning between 2000 and 2009. Glaciers undergoing the most significant retreats (>2 km) accelerated by ~40-190% during the study, indicating widespread sensitivity of glacier behavior in response to climate forcing.
Changes in the Marine-terminating Glaciers of the Geikie Plateau, East Greenland, 2000-2009
Kaitlin Walsh, Ian Howat, Anthony Arendt
Corresponding author: Kaitlin Walsh — walsh.327@osu.edu
Much scientific attention has been focused on measuring ice loss and mechanisms of change of large ice sheets, yet relatively little attention has been given to how ice caps surrounding the periphery of ice sheets are reacting as a result of climate change. There is growing interest in the glaciological community as to how changes in the global climate system are affecting these glaciers and ice caps, which have been observed to be more sensitive to climate change than the larger ice sheets of Antarctica and central Greenland. There have been very limited studies conducted on the glaciers of eastern Greenland’s Geikie Plateau, which has become a location of interest for glaciologists over the past decade as glacial surging and mass loss has been observed on glaciers in the nearby regions. Here, we present changes to the marine-terminating glaciers as observed using Landsat-7 ETM+ imagery to develop a record of changing front positions of these glaciers, as well as ASTER DEMs to quantify elevation change and thinning. Of the 29 marine-terminating glaciers on this plateau, ten were observed to have retreated at least 1 km or greater from 2000-2009, with Kangerdlugssuaq and Sortebrae glaciers on the southeast-facing coast of the plateau each showing retreat of greater than 5 km. Nine of the glaciers in the study area demonstrated notable annual elevation change over the time period studied, and all of these glaciers terminate into the Atlantic Ocean on the eastern facing side of the plateau.
Surface Motion and Strain Field of a Soft-Bedded Glacier in Southeast Iceland
Julie Markus, Ian Howat, Matt King, Bjorn Oddsson
Corresponding author: Julie Markus — markus.30@osu.edu
The purpose of this study is to determine how surface motion, strain rates, and basal stress vary spatially and temporally in order to clarify weaknesses in current understanding of soft-bedded glacier motion using data collected from Breiðamerkurjökull, Iceland. The dynamics of ice motion are the most substantial source of uncertainty in current models of future ice sheet mass-loss and resulting sea level rise. Currently, there is a general lack of quantitative understanding of how glacial basal conditions, such as the hydrology and till rheology at the bed, control ice motion. Glaciers with deformable sediments at their bed (soft-bedded glaciers) are particularly fascinating from the standpoint of glacier dynamics because their flow may be particularly sensitive to changes in basal condition and glacial stress regime, and therefore to climate change. Current models must assume an arbitrary boundary condition for basal stress, leading to potential inaccuracies in results and preventing confident predictions of future changes in ice masses and glacier geometry. This study focuses on the examination of high spatial and temporal resolution surface velocities retrieved from a 12-station GPS grid over a 36-day period to evaluate the variation of glacial motion and strain rates over time on Breiðamerkurjökull. The first specific objective is to identify any short-term velocity variations. The second is to use the surface motion data to calculate strain rates and other components of the force budget. The third objective is to explain the variations in velocity and force budget components while taking into account the glaciomorphic features. Preliminary results reveal three periods of increased surface motion corresponding to periods of rainfall and/or increased temperatures. Along-flow strain rates indicate extension upglacier and compression downglacier during sliding events. By comparing variations in surface velocity, strain rate and basal motion over regions of the glacier with varying ice thickness, basal topography and margin type, we can gain insight into the relationship between ice speed, basal conditions and glacier geometry on timescales of hours to weeks.
Light Field and Optical Properties Measurements of a Supraglacial Melt Pond, Eastern Greenland
William Sneed, Gordon S. Hamilton
Corresponding author: William Sneed — william.sneedjr@maine.edu
Surface meltwater stored in ponds and crevasses on the Greenland Ice
Sheet is known to drain rapidly to the bed and might play a modulating
role in ice dynamics. Because of its wide spatial distribution and
temporal variability, remote sensing methods provide the best means of
quantifying meltwater volumes and their changes with time.

We performed hyperspectral measurements of solar downwelling
irradiance and upwelling radiance (as reflected from the bottom) of
a melt pond on Helheim Glacier, East Greenland. Simultaneous pond depth
measurements were also made, and samples of pond water were acquired
for analysis of optical absorption and attenuation characteristics
using laboratory multi/hyperspectral spectrophotometers.

The downwelling irradiance and upwelling radiance measurements
allow us to calculate the widely use remote sensing reflectance
parameter, Rsubrs, once the upwelling radiance is converted to the
water-leaving radiance by taking into account effects at the water-air
interface. Corrected for atmospheric effects, Rsubrs is the reflectance
measured at the top of the atmosphere (TOA) by satellite sensors,
including the visible/near infrared images collected by the ASTER
sensor on the Terra satellite.

In earlier work, we developed a method for extracting the depth of
glacial melt ponds from ASTER TOA reflectance images. Using our recent
in situ radiance, irradiance, and depth measurements we test the
accuracy of that depth-finding algorithm by applying it to a nearly
concurrent ASTER image. The laboratory absorption and attenuation
analyses provide further validation of some of the initial
fundamental assumptions of our method. Laboratory results as well as
those gathered in the field are used to parameterize a radiative
transfer model that provides an additional source of validation.
Bifurcations and their implications in a low-order model of Arctic sea ice
Dorian S. Abbot, Mary Silber, Raymond T. Pierrehumbert
Corresponding author: Dorian S. Abbot — abbot@uchicago.edu
Significant loss of Arctic sea ice would put immediate strain on Arctic biota, could accelerate the melting of the Greenland ice sheet, and could affect global climate by causing changes in atmospheric and oceanic circulation. Furthermore, as ice-free conditions in the Arctic would allow increased shipping and exploitation of natural resources, an accurate assessment of the probability of such conditions is extremely important for the economic futures of the nations surrounding the Arctic. Therefore it is manifestly in humanity's interest to understand better the behavior of Arctic sea ice and the factors contributing to its current decline.

Improvement in our understanding of Arctic sea ice depends on increased observational constraints on sea ice behavior as well as improved theoretical understanding of the system. Theoretical investigation of Arctic sea ice may be approached using models of a hierarchy of complexity. The massive divergence in sea ice forecasts amongst the complex coupled ocean-atmosphere IPCC models at increased CO2 concentration highlights the need for low-order, conceptual modeling of system behavior in addition to highly-complex modeling. Low-order mathematical modeling can help to establish, for example, the parameter regimes in which threshold behavior is possible and which parameter changes promote threshold behavior. Low-order modeling is not useful for establishing exact parameter values at which threshold behavior would occur.

Eisenman and Wettlaufer (PNAS 2009) proposed an ODE model for Arctic sea ice subjected to seasonally-varying solar forcing. We present an extension of their box model describing both polar and subpolar sea ice. We analyze the dynamics of the coupled system numerically and analytically. Two robust features of this analysis are worthy of note. First, in this system subpolar winter sea ice loss is abrupt and causes complete sea ice loss in the polar region as well. Second, summer sea ice loss does not show threshold behavior and progresses smoothly from south to north.
Distribution and evolution of glacial lakes along the Hindu Kush Himalaya mountain range between 1990 and 2009
J. Gardelle, Y. Arnaud, E. Berthier
Corresponding author: J. Gardelle — julie.gardelle@lgge.obs.ujf-grenoble.fr
In this study, we present a first regional assessment of glacial lake evolution in Hindu Kush Himalaya (HKH), an indirect indicator of glacier changes. Seven sites have been selected between Bouthan and Afghanistan, to capture the climatic variability along the 2000-km long mountain range. For each site, glacial lakes have been mapped with LANDSAT satellite imagery acquired in 1990, 2000 and 2009, using an automatic classification. In the East (India, Nepal and Bhutan), glacial lakes are bigger and more numerous than in the West (Pakistan, Afghanistan), and have grown continuously between 1990 and 2009 by 20% to 65%. On the other hand, during the same period, the glacial lake coverage has shrunk in Hindu Kush (-50%) and Karakorum (-30%). This east/west pattern of lake changes seems in agreement with sparse glaciological measurements that suggest less (or even no) ice loss in the western part of the HKH.
Firn effects in observations of present elevation changes of the Greenland Ice Sheet.
Sebastian B. Simonsen, Louise Sandberg Sørensen, Christine S. Hvidberg
Corresponding author: Sebastian B. Simonsen — sbs@nbi.ku.dk
Observations from the ICESat satellite of changes in surface elevation have shown a rapid thinning at the margins and a thickening in the central parts of the Greenland Ice Sheet. To estimate the present mass loss of the Greenland Ice Sheet from the observed elevation changes the density of the snow/firn/ice involved in the volume change have to be accounted for, along with the response of the firn to changes in surface temperature and accumulation. Different models have been developed to describe the densification of the firn. Based on existing firn densification models a time-dependent estimate of the surface elevation change contribution from the changes in firn compaction will be derived. We use our results to estimate the firn contribution to the changes in surface elevation of the Greenland ice sheet observed by ICESat from 2004-2008, and to estimate the total mass loss over that period.

Assuming local refreezing of melt water the model is both covering wet and dry snow conditions. We use reanalysis data from the ERA-Interim model to provide changes in the surface mass balance parameters needed as input parameter to our calculation. We compare changes in the firn compaction with a steady state to estimate the firn compaction anomaly. The firn compaction anomaly has to be accounted for when converting the observed elevation change from ICESat into a mass change, since changes in firn compaction involves no mass change but may change the surface elevation.

Based on the ICESat observations from the period from 2004-2008 we estimate the total mass loss of the Greenland Ice Sheet. We find that evaluating the total volume of the Greenland Ice Sheet was useful in constraining the parameters of the densification model and validate the spatial distribution of the precipitation modeled by the ERA-Interim. However, the main focus of this work is on the evaluation of the firn model and its application in the conversion from elevation change to mass loss.
Climate Change and Water Supply in Perú: Can the demands of the future be met by the plans of today?
Daniel N. Leavell
Corresponding author: Daniel N. Leavell — leavell.6@osu.edu
The tropical nations of the Andes are beginning to experience the consequences of global climate change. Perú, which has the greatest concentration of glaciers in all of the tropics, is dependent on runoff from its cordilleras for water for hydroelectric generation, irrigation and drinking water supply. Rapid recession of the mountain glaciers will lead to reduced meltwater contribution to stream flow, and diminished water availability in the near future. Huge infrastructural investments are being made to obtain water for the arid Pacific coastal plain; home to nearly 70% of Perú’s 29 million people.

At the current rate of growth, Perú’s capital, Lima, will have a population of 15 million within 25 years. Water supply to Lima, which is barely adequate for the population today, will need to be doubled. Presently this expansion is taking place through the development of a network of reservoirs, canals and tunnels to capture the headwaters of the Rio Mantaro, which flows east to the Amazon basin. North and south of Lima, major diversions of west-flowing rivers have been proposed or constructed to support irrigation of extensive agricultural areas. Sustainability of water supply to these developments is questionable in light of climate change and already conflicts have developed between small-scale farmers in the highlands and large-scale government supported water diversions to the fertile coastal plain.

Desalination of the Pacific waters is often proposed as the next step to sustainable supply for Lima, however this energy-intensive technology may well be out of reach of the Peruvian economy. At present the major source of electricity in Perú is from hydropower, but this too may diminish as a result of the on-going deglaciation of the Andes. Alternatives to hydropower will require either construction of new thermal generating capacity with increased combustion of fossil fuels, or the development of large scale renewable energy projects. Both will be very expensive and may well be beyond the capabilities of Perú.
Mass change of Vestfonna, Svalbard Archipelago
Veijo Pohjola, Rickard Pettersson, Geir Moholdt, Chris Nuth, Leszek Kolondra, Mariusz Grabiec, John C Moore
Corresponding author: Veijo Pohjola — veijo.pohjola@geo.uu.se
During IPY4 (2007-2009) DGPS ground elevation profiles where accomplished by snow-mobile traverses across the 2,500 km2 sized Ice Cap Vestfonna situated in the northeast of the Svalbard Archipelago (80° N, 19° W). The repeated campaigns show local spatial and temporal changes of the ice cap elevation, most likely caused by changes in the wind patterns over the ice cap. Our ground profiles was aimed to follow ICESat profiles (2003-2008) and airborne NASA altimetry (1996, 2002) that criss-crosses the ice cap. Comparisons between ground DGPS altimetry and ICESat altimetry during near-in-time campaigns for both platforms in 2008 show good agreement between both series. Analyzing all the available elevation time series suggest only local changes, but brings no coherent trend in elevation change for the whole ice cap for this specific time period. On the other hand, dynamic measurements of ice flow suggest the ice cap has been in an unstable and negative mode for a century scale time period, with a kinematic ELA 150 m above but the average ELA measured during IPY4. We propose the recent decade has introduced an increase in accumulation rates, serving the ice cap to lower its ELA.
Use of historical elevation data to calculate surface elevation and volume changes of Ha-Iltzuk Icefield in Southwest British Columbia, 1970 - mid-1980s.
Jeffrey VanLooy, Richard Forster
Corresponding author: Jeffrey VanLooy — jvanlooy@radford.edu
Mountain glaciers around the world are important contributors to sea level rise even though they contain only a small percentage of the world's glacial ice. Due to societal concerns of the impacts of climate change it is important to understand in more detail the extent of glacial melting. While continued gathering of glacial data, such as volume, ice density, surface area, and surface elevation is obviously important to understand current glacial conditions, gathering, analyzing, and comparing historical glacial data can be useful in understanding rates of glacial changes especially when compared with historical climatic data. These historical data comparisons help to better understand what future glacial changes might be expected in the face of climate change. While there is often a lack of historical data due to the relatively few observations that have been made over the last century, especially over large and remote regions, some useful data can be found in the form of topographic maps, air photos, and even hand-drawn maps dating back to the earlier half of the 20th century. This particular study adjusts and compares two surface elevation data sets, including topographic map elevations dating to 1970, and photogrammetrically derived elevations from the mid-1980s. Surface elevation and volume changes were calculated using these two data sets for an icefield in a remote region of southwest British Columbia. The results were then compared with a previous study of surface elevation and volume change calculations for the same icefield between mid-1980s - 1999. A comparison of glacier melt rates between the two time periods (1970 - mid-1980s, and mid-1980s - 1999) indicates a doubling of the rate. Climatic data seems to support this doubling rate, as a calculation of Positive Degree Days for the two time periods also indicates a doubling rate.
The historical global sea level budget
John Moore, Svetlana Jevrejeva, Aslak Grinsted
Corresponding author: John Moore — john.moore.bnu@gmail.com
Five decades of tide gauge data on global sea level (GSL) calculated from 1023 tide gauge stations together with global ocean heat content (GOHC) show long periods with little correlation between them. This argues against GOHC being the dominant factor in GSL, and we have shown that it accounts for only about ¼ the rise in GSL. A substantial (about ½) can be accounted for by known glacier and ice sheet estimates of mass balance. There remains about ¼ of GSL rise unaccounted for by the best estimates of both eustatic and thermosteric effects. This fraction also exhibits large variability that is not readily associated with known causes of sea level variability. The most likely explanation of this unknown fraction is underestimated melting, climate- driven changes in terrestrial storage components and decadal time scale variability in global water cycle. Best estimates suggest that land reservoirs have make a negligible net contribution to sea level. Suggesting that variability in the global water cycle comes from ENSO and volcanic impacts, while the unexplained trend component appears to represent an additional continuous ice sheet contribution over the last 50 years. Evidence supporting this hypothesis in recent years comes from improved ice mass loss estimates from GRACE in both Greenland and West Antarctica.
Present-day simulations of Vestfonna ice-cap (Svalbard) with Shallow-Ice and Full-Stokes models
Martina Schäfer, Thomas Zwinger, Kati Laakso, John Moore
Corresponding author: Martina Schäfer — martina.schafer@ulapland.fi
Svalbard is an archipelago in the Arctic Ocean. Nordaustlandet is the second largest island in the archipelago. The island has two major ice-caps: Austfonna and Vestfonna. These ice-caps on Nordaustlandet represent one of the largest
ice-covered areas in the Eurasian Arctic.

In the current project we focus on a present-day simulation of the Vestfonna ice-cap. In this case the Vestfonna and Austfonna ice-caps can easily be modeled separately since the two ice-caps are currently not connected. In a latter step
once the dynamics of these ice-caps is better understood, prognostic simulations over the last 120 ka including both ice-caps together will be conducted.

Our main goals are to compare different types of ice-models (Shallow-Ice and Full Stokes models) as well as to gain a better understanding of the occurrence of basal sliding and possible surge areas.
Even though low temperatures and low balance gradients generally result in low flow rates on the glaciers of Svalbard, the Vestfonna ice-cap is characterized by fast-flow regions (velocities over 200 m yr and periodically even more). The importance of sliding in these regions is shown and a Weertman sliding law is adjusted to reproduce the present-day velocities as obtained from measurements.
In a first step one and the same sliding law coupled to the basal temperature is used over the whole ice-cap. In a second step different sliding laws will be used depending on the basal conditions: hard rock or sediment. The obtained results will be discussed with respect to occuring surging events.

The models used are a Full Stokes Finite Element Model (Elmer, CSCFinland) as well as a Shallow-Ice approximation model (Sicopolis, Ralf Greve).
Both model outputs as well as present-day measurements will be compared.
Data access was made possible by the Kinnvika IPY project consortium.
Response of the ice cap Hardangerjøkulen in southern Norway to the 20th and 21st century climates
Rianne H. Giesen, Johannes Oerlemans
Corresponding author: Rianne H. Giesen — R.H.Giesen@uu.nl
Glacier mass balance changes lead to geometry changes and vice versa. To incorporate this interdependence in the response of glaciers to climate change, models should include an interactive scheme coupling mass balance and ice dynamics. We coupled a spatially distributed mass balance model to a two-dimensional ice-flow model and applied the coupled model to the ice cap Hardangerjøkulen in southern Norway. The available glacio-meteorological records, mass balance and glacier length change measurements were utilized for model calibration and validation. Forced with meteorological data from nearby synoptic weather stations, the coupled model realistically simulated the observed mass balance and glacier length changes during the 20th century. The mean climate for the period 1961-1990, computed from local meteorological data, was used as a basis to prescribe climate projections for the 21st century at Hardangerjøkulen. For a projected temperature increase of 3 degrees Celsius from 1961-1990 to 2071-2100, the modelled net mass balance soon becomes negative at all altitudes and Hardangerjøkulen disappears around the year 2100. The projected changes in the other meteorological variables could at most partly compensate for the effect of the projected warming.
Application of a simple surface mass balance model to glaciers in different climates
Rianne H. Giesen, Johannes Oerlemans
Corresponding author: Rianne H. Giesen — R.H.Giesen@uu.nl
Glaciers and ice caps are found from the Tropics to the high Arctic, in a large variety of climates. Producing glacier volume projections on a global scale requires an efficient method that can handle the mass balance characteristics in different climates. We present a simple surface mass balance model, forced with air temperature and precipitation data. Net solar radiation and energy fluxes dependent on air temperature are calculated separately and together determine the energy available for melt. The parameterizations in the mass balance model were calibrated and validated with measurements from automatic weather stations on glaciers in different regions (Switzerland, Norway, Iceland and Greenland). We show the ability of the model to produce characteristic seasonal cycles of the surface energy and mass balance in different climates. Using global data sets of gridded air temperature and precipitation, we computed equilibrium-line altitudes for glacierized regions, which in general correspond well to observed values.
Investigating basal conditions of a surge type glacier solving an inverse problem
Corresponding author: GAGLIARDINI Olivier — gagliar@lgge.obs.ujf-grenoble.fr
The main objectives of this study is to investigate the basal conditions of a surging glacier. For that, we apply the inverse method proposed by Arthern and Gudmundsson (Journal of Glaciology, in review). This
method is based on an iterative descent algorithm numerically implemented in the finite element code Elmer. Neuman and Dirichlet problems are solved successively in order to minimize the cost function constructed as the norm of the difference between the basal velocities solutions of both problems. The method is applied to the Variegated glacier, a surge type glacier located in Alaska. We use measurements on this glacier carried out by Raymond and Harrison (Journal of Glaciology, 1988) during the quiescent stage of 1966-81 and the surge of 1982-83. Data contain surface velocities as well as the bed and surface topography along the central flow-line.

In a first step, for each set of data obtained at different date, we run the model diagnostically to solve for the basal drag coefficient in order to match the modelled horizontal surface velocities and the
observed velocities. In a second step, inferred basal drag coefficient are analyzed and then integrated in a transient simulation which cover the whole period of the data set, i.e. both quiescent and surge stages.
Results show the contribution of basal sliding in the surge phenomenon and the modification of the basal condition from the quiescent to the surge stages. These modifications can be interpreted in term of
changes in sub-glacial water pressure and runoff.
Flow and rate of ice thickness change at the NEEM drill site, North Greenland
Christine S. Hvidberg, Lars B. Larsen, Susanne L. Buchardt, Dorthe Dahl-Jensen, Sebastian B. Simonsen, Louise S. Sørensen, Rene Forsberg
Corresponding author: Christine S. Hvidberg — ch@gfy.ku.dk
In this work we present preliminary results from a surface strain net survey near the NEEM drill site in North Greenland, and combine with available data to discuss the rate of ice thickness change and flow pattern at NEEM. The NEEM deep drilling site (77.45°N 51.06°W) is located at the main ice divide in North Greenland. A strain net has been established around the NEEM site in 2007 and re-surveyed with GPS in 2008 and 2009. Preliminary data show that the ice flow along the ice divide is W-NW with an average horizontal surface velocity at NEEM of 5.8±0.3 m/a along the ridge, and we estimate surface strain rates at NEEM to be (3.6±1.9)•10-5 a-1 (longitudinal) and (13.1±0.4)•10-5 a-1 (transverse), i.e. flow is divergent and slightly extending along the ridge. Radar layers along the ridge upstream from NEEM have been analyzed and inverted to provide upstream accumulation rates, basal melt rates, and velocity depth profiles. Surface velocities and velocity depth profiles provide an estimated ice flux used to infer the local rate of ice thickness change from the depth-integrated continuity equation. Using preliminary results, we estimate the local rate of ice thickness change to be ∂H/∂t = (-0.01±0.17) m/a. We find agreement between our estimate and the surface elevation change in the NEEM area obtained by the ICESat mission.
We combine all available data, including surface strain rate data at NEEM and at NorthGRIP (previous drill site 1996-2003 located at the main ridge 365 km upstream from NEEM) and internal radar layers between NorthGRIP and NEEM, to discuss the flow pattern along the ridge and in particular around the NEEM site. We compare our results with observation from the ICESat and GRACE satellite missions, and discuss possible implications for the dynamic stability of the ice sheet in this region.
Humboldt Glacier, Greenland sub-marine melt rates derived from CTD/current casts
Jason Box, Alun Hubbard, Richard Bates
Corresponding author: Jason Box — box.11@osu.edu
Abstract A larger de-stabilization of ice sheets is threatened from oceanic than atmospheric climate change. A chain of oceanographic profiles were casts in front of the Humboldt Glacier terminus, northwest Greenland summer 2009 with the Greenpeace ship Arctic Sunrise. A heat and mass budget closure scheme is applied to derive effective sub-marine ice melt rates. The results are discussed in context of seasonal climate and recent oceanic and atmospheric climate change.
Greenland marine terminating glacier front area changes 2000 - 2009
David Decker, Dr. Jason Box
Corresponding author: David Decker — decker.146@gmail.com
The sea ice in Nares Strait, separating Greenland and Ellesmere Is Arctic Canada did not consolidate in 2006/2007 and 2008/2009. In 2007 the ice bridge did not form, thus, resulted in the highest outflow of Arctic sea ice between 1997 and 2009. Since the dawn of the satellite era the channel has rarely been clear of sea ice north of Smith Sound. Unconsolidated sea ice was advected south of the Lincoln Sea ice bridge by June 2009. It remains unclear whether this expanded polynya condition is part of a changing climate signal.
Polynyas play a pivotal role as they are thought to model open-water systems for how the Arctic will respond to regional and circum-Arctic oceanic and atmospheric forcing; enable navigable waterways for imports/exports and fisheries in the Canadian Arctic; and provide important feeding areas for marine mammals.

AMSR-E 12.5 km sea ice concentration and MODIS surface temperature product (MOD28) are used to investigate the seasonal 2009 sea surface temperature and sea ice concentration anomaly. The anomaly is calculated using daily imagery to get a monthly mean and a monthly multi-year climatological baseline from the period 2002-2007. Spring 2009 sea ice concentration were 10 % below average up the center of the channel north of Smith Sound where the SST anomaly is normal. SMMR and SSM/I 25km resolution data indicate a -32% below normal sea ice concentration in June 2009 with respect to the 1979-2007 base period. In Summer, 2009 a -70% sea ice concentration anomaly appears in southeast Kane Basin and Northern Baffin bay where the SST anomaly was +1.8 and +2.0 degree C, respectively.

During the 2009 summer the Humboldt Glacier front lost -31.6 sq. km amid warmer than normal Kane basin SSTs. Petermann Glacier did not exhibit a significant area change in 2009 summer, but did during the record-warm 2008 summer. The loss of sea ice may cause Petermann and Humboldt glacier to buttress.
Alpine Glaciers in the Himalayas, New Zealand and Norway: Investigation of Inorganic Trace Element Abundances
Kimberly A. Casey, Oddvar Røyset, Ruikai Xie, Harry Keys
Corresponding author: Kimberly A. Casey — k.a.casey@geo.uio.no
Alpine glacier observations have been conducted in Khumbu Himalaya, Nepal; New Zealand; southern Norway and Svalbard. 89 surface glacier ice, snow, glacial melt water, sediment and vegetation samples were collected in 2009 and 2010. Inorganic trace element measurement was performed via Inductively Coupled Plasma Mass Spectrometry acid digestion on all samples. Additionally, glacier sediments from debris covered glaciers in Khumbu Himalaya, Nepal were analyzed for inorganic trace element concentration via X-ray Fluorescence Spectrometry. The influence of climate, precipitation, both large-scale and regional atmospheric circulation, as well as surrounding lithologic and hydrologic characteristics that contribute to the observed glacier- and sample-specific trace element abundances are discussed. Further, anthropogenic vs. natural trace element abundance sources are differentiated. Trace element abundance and relative geochemical signature results from this observation set are compared with existing glacier and ice sheet trace element data sets. Recent scientific discussion suggests the use of trace element presence and concentration in snow as an atmospheric background monitoring tool. From the compiled global snow trace element data set, one suggested background standard location of Mt. Everest snow will be evaluated. Finally, the presence and concentration of inorganic trace elements has a clear ecosystem and societal impact - especially in regions where glacial runoff is directly used for water resources, such as the Khumbu Himalayas. While some trace elements are essential to life (for example, iron, manganese, copper and zinc) other trace elements (such as mercury, cadmium and lead) are not required by living organisms in any concentration. Of course all metals, including the essential trace elements are toxic to living organisms in high exposure levels. As alpine glacier melt and mass loss continues (including the vast thinning of Himalayan glaciers), understanding of inorganic trace element abundances is relevant to many of the above mentioned topics including water resources, ecosystem impacts, and atmospheric circulation. This study adds to the understanding of propagation of geochemical signatures in glacier environments.
Greenland's disappearing ice: drivers, responses, and impacts
Jason Box, David Decker
Corresponding author: Jason Box — box.11@osu.edu
NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) imagery are used to calculate inter-annual end of summer glacier front area changes at 34 major Greenland ice sheet marine-terminating outlets over the 2000-2009 period.

The 2009 area compared with 2008 indicates a net marine-terminating ice area loss of 109 sq km. The total net cumulative area change from year 2000 (when our survey begins) to 2009 is -966.8 sq. km, a loss equivalent with an area more than 11 times the area of Manhattan Is. (87.5 sq. km) in New York, USA. The marine-terminating ice area change for these glaciers is -104 sq. km per year, the 2009 loss being within 3% of the linear fit. Thus, he loss rate has been nearly constant. Though, on a glacier by glacier basis from year to year, the loss rate is not constant.

To put the recent 9 end of summer net annual changes into a longer perspective, glacier front position information from the past century are also incorporated.

The drivers of the glacier changes include surface and oceanic warming. Marine-terminating glaciers are very sensitive to even small changes in ocean heat content. The impact of the observed glacier changes is interpreted using glaciological theory and regional climate observations.
Compilation of a glacier inventory for the western Himalayas from satellite data: Challenges and results
Holger Frey, Frank Paul, Tazio Strozzi
Corresponding author: Holger Frey — holger.frey@geo.uzh.ch
Detailed digital glacier inventories are a basic requirement for the assessment of climate change impacts in mountain regions. Detailed information about glaciers and glacier changes in the Himalayas are missing as recent debates have shown. Due to the high variability of the climatic regime (monsoon type to continental) and the special glacier characteristics in this region (e.g. debris-cover, avalanche fed), any regionalization of the behaviour of individual glaciers is error prone. Moreover, runoff from these glaciers feed the Ganges and Indus rivers, which are the lifeline of hundreds of millions of people and makes the compilation of such a dataset especially important.

To provide a baseline dataset for improved modeling and change detection, a glacier inventory for the regions Jammu and Kashmir, Himachal Pradesh, and Uttaranchal in the western Himalaya was compiled in the framework of the ESA project GlobGlacier. Based on eight Landsat ETM+ scenes, glaciers were mapped by band-ratioing and manually corrected by deleting wrongly classified water bodies and adding debris-covered glacier parts. Local orographic clouds that covered some glaciers caused an additional challenge. In part, this problem was solved by the use of multi-temporal imagery. Due to high solar elevation and a related lack of contrast, it was nearly impossible for many debris-covered glacier tongues to accurately delineate their extent from visual interpretation of optical images. To confront these problems, five coherence image pairs from ALOS PALSAR acquired during summer 2007 were used. The movement-related decorrelation over glaciers is in strong contrast to the non-moving surrounding terrain and allows precise delineation of their extent. Basic topographic glacier inventory parameters are calculated from the void-filled version of the SRTM 3 DEM. The final inventory will be provided to the GLIMS glacier database for free access.
Multi-sensor Assessment of Larsen B Tributary Glacier Elevations 2001-2009, Antarctica
Christopher A. Shuman, Ted A. Scambos, Etienne Berthier
Corresponding author: Christopher A. Shuman — christopher.a.shuman@nasa.gov
Since before the break-up of the Larsen B Ice Shelf in early 2002, multi-sensor elevation data acquired over its feeder glaciers has subsequently quantified remarkable decreases in ice elevations, especially in comparison to similar glaciers still constrained by a remnant of the ice shelf. This study used a combination of ASTER and SPOT5-HRS derived DEMs, Airborne Topographic Mapper laser altimetry, and ICESat laser altimetry to quantify the temporal and spatial nature of the drawdown caused by the loss of the Larsen B. For example, during late 2004, a portion of the Crane Glacier's lower trunk began a localized elevation loss exceeding 40 cm/day for about 3 months and totaling almost 100 m in just over a year. In total, this location lowered by 180 m over 2001-2006 with substantial elevation losses extending >25 km further inland along the South and West Crane tributaries by late 2006. The Hektoria/Green/Evans system also responded rapidly to the loss of the Larsen B (e.g. Scambos et al., 2004) with rapid ice edge retreat and 100+ m elevation losses between 2001 and 2006. Grounded ice volume losses exceed 12 km3 in the long Crane system and 27 km3 in the broader Hektoria system over that time frame. Continued assessment of these elevation changes will enable better predictions of the drawdown likely to be experienced by the nearby Flask and Leppard Glaciers (still buttressed by the Larsen B remnant). Other glaciers like the Jorum may be a better analog for the shorter glaciers discharging into the Larsen C Ice Shelf.
Untapped climate ice archives at risk due to global warming: the case of Mt. Ortles, Eastern European Alps
Paolo Gabrielli, Luca Carturan, Jacopo Gabrieli, Roberto Dinale, Karl Krainer, Helmut Hausmann, Mary Davis, Victor Zagorodnov, Roberto Seppi, Carlo Barbante, Giancarlo Dalla Fontana and Lonnie Thompson
Corresponding author: Paolo Gabrielli — gabrielli.1@osu.edu
Compared with the polar regions, relatively few ice cores have been extracted from the highest mountain glaciers at low latitudes. Together with the numerous polar ice records, the information obtained from these alpine ice cores are compelling as they point out similarities and differences in the past climatic dynamics at high and low latitudes. Due to the recent rise of the freezing isotherm, several high altitude glaciers that were suitable drilling sites until a few decades ago are now affected by meltwater percolation and ablation. Unfortunately, a significant number of these glaciers are still undrilled and their potentially valuable ice core archives have not yet been safely secured in storage freezers.
Mt. Ortles (3905 m a.s.l., South Tyrol, Italy) is the highest mountain of the Eastern European Alps and is located only ~30 km from where the mummy of the 5200 years old Tyrolean Ice Man was discovered. Ortles’s upper glacier, Alto dell’Ortles, presents a unique opportunity to obtain the first, and perhaps the only, paleoclimate record from an ice core drilled in this area of the Alps. In June 2009, we performed the first study of the glaciological characteristics of the Alto dell’Ortles glacier at ~3830 m a.s.l. The maximum depth of this glacier is ~75 m and the estimated firn/ice transition lies at ~24 m. Firn layers and ice lenses were observed down to 10 m and the temperature at this depth (-1.2 °C) was just below the pressure melting point. The chemical-physical analyses of firn samples and a simple model provide evidence that the mass balance of the upper part of the Alto dell’Ortles glacier was positive during the last few years. The seasonal chemical-physical signal is still preserved in several parameters within the shallow snow and firn layers, indicating that a climate history may be retained in Mt. Ortles ice.
However, the observation of ice lenses and an incipient “smoothing” of the seasonal chemical-physical signal show the recent occurrence of melting-refreezing cycles. Indeed our mass balance model indicates that meltwater percolation took place within the firn during the recent warm summers. This suggests that an increase in frequency and/or intensity of meltwater percolation could endanger the preservation of this potentially unique glacial archive. In light of the strong warming observed and predicted in the Mediterranean region during the next few decades, this unique paleoclimate record in the Eastern European Alps is at risk.
Tropical Glaciers, Recorders and Indicators of Climate Change, are Disappearing Globally
Lonnie G. Thompson, Ellen Mosley-Thompson, Henry H Brecher, Mary Davis, Ping-nan Lin
Corresponding author: Lonnie G. Thompson — thompson.3@osu.edu
Tropical climate variability is dominated on interannual time scales by monsoons and particularly especially by the El Nino-Southern Oscillation (ENSO) with its strong impacts on meteorological phenomena that either directly or indirectly affect most regions on the planet and their populations. Common teleconnections from the tropics to the extra tropics affect the strength of the Aleutian low and the westerlies, variations in convective activity that control flooding and drought, and modulation of tropical storm intensities. New ice core records from the Quelccaya, Coropuna and Hualcán ice fields in Peru, the Naimona’nyi Glacier in the Himalayas and from the few remaining glaciers in Papua, New Guinea provide a more global perspective of climatic and environmental changes. Recent evidence of the continued and accelerating ice lost around the globe is disturbing. This paper examines the ice core histories that provide the longer term context needed to assess the significance of the magnitude and rate of current ice loss. Some tropical ice fields have provided a continuous, 2000-year long, annually-resolved proxy record of climatic and environmental variability preserved in the oxygen and hydrogen isotopic ratios, the concentrations of mineral dust and various chemical species and the net mass accumulation. These records provide an opportunity to examine the nature of tropical climate variability in greater detail, and to extract new information about ENSO and monsoon-linked climate phenomena. No other tropical glacier captures this annual variability better than the Quelccaya ice cap in southern Peru. The Quelccaya records can be considered virtually the “holy grail” of high resolution ice core records from tropical glaciers. They show unequivocally that the recent acceleration of ice retreat in this Andean region is not driven by precipitation changes. The well-documented ice loss on Quelccaya in the Andes, Naimona’nyi in the Himalayas, Kilimanjaro in eastern Africa, and on Puncak Jaya in Papua, New Guinea paints a grim future for glacier histories from the tropics. This paper will present an overview of ice loss in these globally representative tropical regions as well as a time perspective on the significance of the current changes. This ongoing melting of high-altitude, low-latitude ice fields is consistent with model predictions for a vertical amplification of temperature in the tropics and has serious implications for the people who live in these areas and hence are on the front lines of the global climate change crisis.
A laboratory-scale iceberg-filled water tank: Toward an experimental approach to understanding the physics of abrupt ice-shelf collapse
Justin Burton, Dorian S. Abbot, Jason M. Amundson, L. Mac Cathles, Nicholas Guttenburg, Douglas R. MacAyeal, Wendy W. Zhang
Corresponding author: Douglas R. MacAyeal — drm7@uchicago.edu
One of the important modes of disappearing ice is the abrupt fragmentation of ice shelves and fjord-bound glacier tongues that buttress inland ice flow. As events along the Antarctic Peninsula have shown, this disintegration style is clearly enabled by environmental changes that involve both surface and basal mass balance effects, and possibly also the influence of ocean swell. Once enabled, however, the short, hours to days time-scale over which an ice shelf or ice tongue disintegrates appears to be influenced strongly by the localized mechanics of iceberg-covered water bodies. In particular, the underlying physics governing great numbers of capsizing, or otherwise moving, icebergs that are in close contact, and that are able to influence each other via water-waves, appears to be a fruitful avenue of inquiry. To gain further insight into the parameters (e.g., iceberg geometry aspect ratio, crevasse density) that control the disintegration process, and to seek observable variables that may give insight into the underlying exchanges of energy involved in massed iceberg movements, we have constructed a laboratory-scale ice-shelf collapse apparatus.

The experimental apparatus consists of a 40-meter water tank that is 1 meter wide. Within the tank, we introduce fresh water and approximately 200 rectangular blocks of plastic having the appropriate density contrast to mimic floating icebergs. The plastic blocks are constructed by linking several thin layers into a block-like form so as to control the aspect ratio of the initial thickness to width, and thus to determine the energy released when these blocks tip over. The blocks are initially deployed in a tight pack, with all blocks arranged in a manner to represent the initial state of an integrated ice shelf that is riven with incipient iceberg-detachment rifts. The system is allowed to evolve through time under the driving forces associated with the capsize of various blocks both within the dense pack and at the leading ice front. Digitized photography is used to extract information about how the arrangement evolves between states of quiescence and states of mobilization.
Numerical model of ice melange expansion during abrupt ice-shelf collapse
Nicholas Guttenburg, Dorian S. Abbot, Jason M. Amundson, Justin C. Burton, L. Mac Cathles, Douglas R. MacAyeal, Wendy W. Zhang
Corresponding author: Douglas R. MacAyeal — drm7@uchicago.edu
Satellite imagery of the February 2008 Wilkins Ice-Shelf Collapse event reveals that a large percentage of the involved ice shelf was converted to capsized icebergs and broken fragments of icebergs over a relatively short period of time, possibly less than 24 hours. The extreme violence and short time scale of the event, and the considerable reduction of gravitational potential energy between upright and capsized icebergs, suggests that iceberg capsize might be an important driving mechanism controlling both the rate and spatial extent of ice shelf collapse.

To investigate this suggestion, we have constructed an idealized, 2-dimensional model of a disintegrating ice shelf composed of a large number (N~100 to >1000) of initially well-packed icebergs of rectangular cross section. The model geometry consists of a longitudinal cross section of the idealized ice shelf from grounding line (or the upstream extent of ice-shelf fragmentation) to seaward ice front, and includes the region beyond the initial ice front to cover the open, ice-free water into which the collapsing ice shelf expands. The seawater in which the icebergs float is treated as a hydrostatic fluid in the computation of iceberg orientation (e.g., the evaluation of buoyancy forces and torques), thereby eliminating the complexities of free-surface waves, but net horizontal drift of the icebergs is resisted by a linear drag law designed to energy dissipation by viscous forces and surface-gravity-wave radiation. Icebergs interact via both elastic and inelastic contacts (typically a corner of one iceberg will scrape along the face of it’s neighbor). Ice-shelf collapse in the model is embodied by the mass capsize of a large proportion of the initially packed icebergs and the consequent advancement of the ice front (leading edge).

Model simulations are conducted to examine (a) the threshold of stability (e.g., what density of initially capsizable icebergs is needed to allow a small perturbation to the system evolve into full-blown collapse of the ice shelf? What proportion of uncapsizable icebergs prevent a collapse?), (b) the rates of mobilization and their dependence on iceberg geometry (e.g., what determines the speed at which the expanding ice mélange moves into the open, ice-free water?), and (c) the factors that promote the arrest of the system (e.g., are there circumstances where only partial collapses can occur?). Results of simulations are compared with observational parameters derived from satellite imagery, seismic analysis and laboratory experiment to determine what aspects of the numerical model’s physical formulation may have most relevance to the disappearance of ice shelves.
The glaciological mosh pit
Douglas R. MacAyeal, Dorian S. Abbot, Jason M. Amundson, Justin C. Burton, L. Mac Cathles, Nicholas Guttenburg, Wendy W. Zhang
Corresponding author: Douglas R. MacAyeal — drm7@uchicago.edu
In the ancient and venerable language of the Inuit, it was called "Sikkusak". Then it was seen in Antarctica, and it was necessary to use the lingua franca term: "ice melange". But when it became clear that it released gravitational potential energy in such quantities and at such rates as to drive the most destructive behavior ever unleashed on the vulnerable floating termini of Greenland’s outlet glaciers and Antarctica’s ice shelves, only the Jamaican Patois seemed appropriate: the glaciological "mosh pit".

So, what's the glaciological mosh pit? It’s all of the following entities: it's the stuff which both energizes the fragmentation of ice-shelves and de-energizes the calving faces of Greenland outlet glacier termini, it's the lifeless end state of icebergs that calve into fjords, it's the place where icebergs interact with the ocean by thermodynamic, but especially by wave-dynamic manners, and ultimately it’s the place of violence where the great mash-up of what was once statuesque and proper "glacier ice" leads to the residue of disappearing ice.

This presentation will review the processes involved in the glaciological mosh pit that drive abrupt ice disappearance events. Most importantly, a summary of the fundamental processes of ice and ice/water dynamics active in the mosh pit will be presented. The summary will begin with an explanation of how to calculate the gravitational potential energy released by iceberg capsize, and thus radiated as ice-destructive tsunami waves. As research progress permits, the summary will extend to cover numerical simulations of iceberg tsunamigenesis, iceberg interaction within iceberg-filled fjord waters and low-order (highly idealized) models of ice-shelf collapse that mimics popping popcorn.
The landslide blessing and curse for glaciers: obliviousness to climate warming, and sudden disarticulation
Jeffrey S. Kargel, Gregory Leonard, Roberto Furfaro
Corresponding author: Jeffrey S. Kargel — jeffreyskargel@hotmail.com
Large supraglacial landslides have dramatic effects on glacier dynamics and may cause some retreating glaciers to advance, stabilize, or slow their retreat. The chief mechanism is not increased loading, as once thought. Unlike ordinary medial moraines, which are fed onto glacier surfaces more or less continuously, landslides represent stochastic projections of debris onto glacier surfaces. Like any thick debris deposits, landslides have a pronounced insulating/protective effect on ice beneath the debris; if the landslides are large, they can have a substantial effects on mass balance. The positive effect on mass balance becomes stronger as the debris is swept farther down the ablation zone, until eventually the debris is compressed into a narrower zone near the terminus, where it can help create a towering ice-cored end moraine while abruptly diminishing its influence on net glacier mass balance. Landslides that occur high in the accumulation area may become immediately buried and thus have no influence on mass balance until eventually the deposit exits the interior of the glacier somewhere onto the glacier’s ablation surface, where it then causes a positive influence on mass balance. These effects are large only if the landslide is large. In large glaciers in tectonically highly active areas, such as in the Chugach Mountains (Alaska), landslides big enough to significantly affect the glacier’s mass balance may occur episodically about once or twice per century. This is also the characteristic glacier response timescale and time for major anthropogenic global warming. Large landslides are stochastic and their protective influences vie with climate change and the time scales for dynamical responses to perturbations. Thus, landslides can help explain the dynamical complexity and contrasting behaviors of some otherwise similar glaciers. In theory, as global warming may spur glacier thinning and retreat in the ablation zones, fractured mountain slopes and moraines are debuttressed and thawed, thereby contributing more frequent and perhaps larger landslides. Large landslides can cause glaciers to “overextend,” as mentioned above, but when the debris is finally swept to the terminus, mass balance may suddenly shift in a negative direction. Furthermore, supraglacial lake formation in thermokarstic, hummocky landslide debris-covered glacier tongues may precipitate rapid wastage and disarticulation of those tongues. Increased warming may speed the rates of glacier retreat, but increased landslides may occasionally oppose warming, until eventually they accentuate them. Landslides giveth, and landslides taketh away.
A new method to infer sub ice-shelf melting/refreezing.
Antoine PETRELLI, Gael DURAND, Catherine RITZ
Corresponding author: Gael DURAND — durand@lgge.obs.ujf-grenoble.fr
Together with calving, sub ice-shelves melting is an important component of the Antarctic global mass balance. Here, we focus on basal conditions below ice-shelves, and aim to evaluate rates and spatial distribution of melting/refreezing under ice-shelves using surface measurements (i.e. surface elevation, accumulation and velocities). Studies done so far have estimated sub ice-shelf melting using the mass conservation principle with a uniform ice-density. However it is now well known that sea water may refreeze below the ice-shelves and produce the so-called marine-ice which, compared to meteoric ice, has a higher density. Because marine ice may represent a consequent (substantial) fraction of the total ice-shelf thickness, ignoring change in density may be misleading. Here, we present a method which allows to take density variations into account and calculates, along flow tubes covering shelf areas, the melting/freezing rate and ice thicknesses from both meteoric and marine ices. The method is first evaluated and compared to previous methods using synthetic data before being applied over the major Antarctic ice-shelves.
Requested Bedrock Accuracy to Model Antarctic ice Dynamics
Gael DURAND, Olivier Gagliardini, Lionel FAVIER, Thomas ZWINGER, Emmanuel LE MEUR
Corresponding author: Gael DURAND — durand@lgge.obs.ujf-grenoble.fr
Proper knowledge of bedrock elevation is a crucial input parameter for ice-sheet modeling. For obvious reasons of inaccessibility, its knowledge is fragmented, and the question arises to where future radar measurement campaigns should focus on, especially in the context of global warming and related current ice-sheet dynamics changes. By using a full-Stokes finite element code with a proper mechanical solution of the contact problem at the grounding line, the sensitivity of an ice flow model on the accuracy of the bedrock description is examined. We show that mass exchange between ice-sheet and ocean is poorly affected by a crude knowledge of the bed elevation in the interior of the continent. Conversely, bedrock requires to be known at a minimum $2$ km sampling scale in the vicinity of coastal regions in order to avoid unrealistic unstable behavior of outlet glaciers.
Enhancement factors for grounded ice and ice-shelves inferred from an anisotropic ice flow model
Corresponding author: GAGLIARDINI Olivier — gagliar@lgge.obs.ujf-grenoble.fr
Polar ice is known as one of the most anisotropic natural material. For a given fabric, the polycrystal viscous response is strongly dependant on the actual state of stress and strain-rate. Within an ice-sheet, grounded ice parts and ice-shelves present completely different stress regimes, so that one should expect completely different impact of ice anisotropy on the flow. The aim of this work is to quantify, via the concept of enhancement factors, the influence of ice anisotropy on the flow of grounded ice and ice-shelves. To this purpose, a full-Stokes anisotropic marine ice-sheet flow line model is used to compare isotropic and anisotropic velocity fields. From this full-Stokes results, a definition of enhancement factors for grounded ice and ice-shelves, coherent with the asymptotical models used for these regions, is proposed. Realistic values for the enhancement factors induced by ice anisotropy for grounded ice and ice-shelves are then estimated.
Comparing glacier dynamics and glacier fluctuation in the eastern and central Himalaya
Umesh K. Haritashya, Tood Longbottom
Corresponding author: Umesh K. Haritashya — Umesh.Haritashya@notes.udayton.edu
In the Indian sub-continent, major river originates from the snow and glacier cover Himalayan mountain and provide substantial amount of runoff to the lowland areas, but these mountains have seen extensive climate and glacier fluctuations in the Quaternary. It is widely recognized that Himalayan cryosphere is highly sensitive to climatic fluctuation due to the relatively large distribution of snow and ice, the altitude range, and plentiful and increasingly debris–covered glaciers, yet very little information on changing conditions in the Himalayas have been reported. Only a few studies based on observation made over limited time periods are available for a few specific glaciers, which is not at all representative of the entire area. Climate simulations representing a carbon-dioxide-loading scenario suggest that Himalaya, could exhibit even greater rates of change in future, and therefore, it is essential to asses these glaciers as a cluster feature and not an individual glacier. Consequently, our objective was to assess and compare glacier dynamics and glacier fluctuation in and around two major massifs in the east and central Himalaya. Since these glaciers are so large in scale and reside in extremely remote areas, contemporary studies rely primarily on satellite imagery. Specifically, this study uses multi-temporal satellite imagery from LANDSAT, ASTER, and IRS. Images were orthorectified and radiometrically calibrated, and a digital elevation model was generated using ASTER data. Our result shows that glaciers in each geographic region are extremely complex and exhibited starkly different characteristics both spatially and temporally. Generally proceeding from the central to the east the glaciers seems to be thinning in overall debris cover, and downwasting and retreat pattern. In addition, the increase in meltwater production is evident on some glaciers, as revealed by variation in the frequency and size of supraglacial and proglacial lakes. These cryospheric changes can be linked to regional-scale climate change that is affecting the water resource supply in this region. There is an urgent need to conduct fieldwork to obtain direct measurements and develop long-term database to further document rapid change due to climate forcing.
Numerical investigation of thermal regime of ground under and around two lakes on the Alaskan Arctic Costal Plain
Feng Ling, Ying Lu, Qingbai Wu, Tingjun Zhang
Corresponding author: Feng Ling — lingf@zqu.edu.cn
One of the most obvious manifestations of the hydrological system at work in the Arctic is the vast number of thaw lakes that occur in tundra regions. These lakes constitute a heat source, giving rise to anomalous heat flow and temperature conditions in the ground. Consequently, a perennial thaw layer between the thaw lake bottom and the permafrost surface forms and increases in thickness over time. This study investigates numerically the long-term impact of two shallow thaw lakes on the thermal regime of ground under and around the lakes on the Alaskan Arctic Coastal Plain. The numerical model used in this study is a two-dimensional unsteady finite element model for heat transfer with phase change under a cylindrical coordinate system developed by the authors in previous studies. Based on past researches of permafrost and thaw lakes at Barrow, Alaska, two simulation cases of 1) just one lake with a long-term mean lake bottom temperature of 2.0supoC and lake depth of 2.0m; and 2) two lakes with lake depth of 2.0m and the long-term mean lake bottom temperatures of 2.0supoC and 1.0supoC, respectively. were conducted. The radiuses of the two lakes both are set at 300m, and the total radius of the analysis domain, which is also the distance of the central lines of the lakes, is set at 1000 m. the upper boundary of the analysis domain is set at the lake bottom off the shore, and at a depth of 0.5 m below the ground surface on the shore, and the lower boundary is set at 500 m, 100 m below the permafrost base. The simulated results indicate that shallow thaw lakes are a significant heat source to ground. It is concluded that variation of long-term mean lake bottom temperature has a significant influence on ground thermal regime.
A new glacier inventory for Western Alaska
Raymond Le Bris, Holger Frey, Tobias Bolch, Frank Paul
Corresponding author: Raymond Le Bris — rlebris@geo.uzh.ch
Glaciers and ice caps are essential components of studies related to climate change impact assess¬ment. Glacier inventories provide the required baseline data to perform the related analysis in a con¬sistent and spatially representative manner. In particular, the calculation of the current and future contribution to global sea-level rise from heavily glacierized regions such as Alaska is a major demand. Unfortunately, most of the digitally available data of glacier extent is quite rough and based on rather old maps from the 1960s. Accordingly, the related calculations and extrapolations are impre¬cise and an updated glacier inventory is urgently required for this region.

Within the framework of the ESA project GlobGlacier, we compiled a new glacier inventory for a large part of Western Alaska (incl. Kenai Peninsula, Tordrillo, Chigmit and Chugach Mts.). Well established automated glacier mapping techniques (band ratio) are applied to map clean to dirty glacier ice. However, many glaciers are covered by optically thick debris or volcanic ash and outlines were manually corrected during post-processing. Prior to the calculation of drainage divides from DEM-based watershed analysis, we per¬formed a cross-comparative analysis of DEMs from USGS, ASTER (G-DEM) and SRTM1 for Kenai Peninsula. This resulted in the decision to use the USGS DEM for calculating the drainage divides and most of the topographic inventory parameters, and the more recent G-DEM to derive minimum elevation for each glacier.

We used 9 scenes from the USGS Landsat archive acquired between 2002 and 2009 to map c. 9000 glaciers (>0.02 kmsup2) for a total area covering c. 16,250 kmsup2. Large parts of the area (47%) are covered by only few (31) but large (>100 kmsup2) glaciers, while glaciers <1 kmsup2 contribute only 7.5% to the total area, but 86% to the total number of analysed glaciers. However, these percentages vary with the specific mountain range analysed. The spatial analysis of mean glacier elevation (as a proxy for the ELA) revealed a strong increase from the glaciers close to the coast towards the interior of the country (from about 100 to 2960 m a.s.l.). This more regional trend has also a high local variability, indicating that the response of glaciers to climate change will probably differ locally. The entire inventory data will finally be made available in the GLIMS glacier database.
Characterising the Surface of the Greenland Ice Sheet in a High Resolution Regional Climate Model (HIRHAM5)
Ruth Mottram, Gudfinna Adalgeirsdottir, Philippe Lucas Picher, Ole Bøssing Christensen, Jens Hesselbjerg Christensen
Corresponding author: Ruth Mottram — RUM@dmi.dk
HIRHAM5 is a high resolution regional climate model that has been coupled to an ice sheet model
(PISM, the Parallel Ice Sheet Model) for medium and long term projections of the Greenland Ice Sheet.
Mass balance is calculated within HIRHAM5 using an energy balance model, for which reason the surface scheme of the climate model has been upgraded over glaciers and ice sheets to account for important boundary layer processes. Here, we explore the impact of including these processes on the calculated mass budget and assess the success of HIRHAM5 in representing key elements of the surface energy fluxes. Test runs of HIRHAM5 over the ERA-40 and ERA-Interim periods can be validated against existing datasets and show the success of this approach in calculating ice sheet surface mass balance.
Climatic controls of glacier distribution and glacier changes in Austria
Jakob Abermann, Michael Kuhn
Corresponding author: Jakob Abermann — jakob.abermann@uibk.ac.at
In this study we aim at connecting information on glacier extent (for the year 1998) and its changes (between 1969 and 1998) with general climatic conditions and an analysis of climate change in the Austrian Alps. We perform our investigations by using two complete glacier inventories, a homogenized, gridded precipitation dataset as well as ERA40 re-analysis data of air temperature at different pressure levels. We found a relation between glacier median elevation and the mountain area's peak elevation. Apart from that, spatial gradients of temperature and precipitation can explain general patterns of glacier extent. Low elevations can have a glacier cover due to winter precipitation above average and/or strong dynamic ice-supply. We found a climatic limit that allows debris-free Alpine glaciers to exist at elevations of about 2000 m a.s.l. where mean summer temperatures (JJA) exceed 4°C.
Total changes in both relative area and volume (mean thickness) have been strongly negative between 1969 and 1998. A period of glacier advances in the late 1970s and early 1980s has been observed. The analysis of climatic reasons for these fluctuations shows that temperature anomalies are the driving factor for both positive and negative glacier changes and occur homogeneously throughout the study area. A sequence of large positive temperature anomalies in the early 1980s and after 1990 is the major reason for the general retreat. There is no significant trend in precipitation. We discuss regional differences of glacier changes and their reasons. We explain them mainly with decreased mass-turn-over in recent years that results in increased volume loss of large, low altitude glaciers compared to smaller, higher ones. This affects more heavily glacier-covered regions stronger than regions with only few and small glaciers and is reflected in the spatial pattern of the observed glacier changes in Austria.
Modelling annual mass balances of all Austrian glaciers since 1969
Jakob Abermann, Michael Kuhn
Corresponding author: Jakob Abermann — jakob.abermann@uibk.ac.at
In this study we apply a glacier-climate model to reconstruct annual glacier mass balances for all Austrian glaciers (900 glaciers, 470 km2) back to 1969. We calibrate a positive degree-day (PDD) model using air temperatures from ERA40-reanalysis data at different pressure levels (600, 700 and 850 hPa) with temporally and spatially changing lapse rates. For precipitation we use a 10'-gridded dataset on a monthly basis. Two complete glacier inventories (1969 and 1998) serve as the glaciological input parameter and the volume changes that occurred between these dates serve as the boundary condition that is aimed to be reproduced.
We perform several model-runs refining the spatial and vertical variability of the input-parameters in order to reproduce the measured mean annual mass balances of selected glaciers. A spatially and vertically constant degree-day factor (DDF) is not able to reproduce the observed changes realistically. Therefore we define a vertical gradient of DDFs in order to account for changes in the radiation budget due to changing surface characteristics (i.e. albedo). A spatially variable DDF improves the result significantly and we find a strong correlation between the median elevation of a glacier and the DDF at this elevation that best represents the total volume change. The lower a glacier's median elevation, the less melt occurs at a given elevation and temperature. We attribute this to the fact that lower-elevated glaciers are generally in regions with more winter precipitation leading to a later exposition of bare ice in the year and thus being covered longer with snow cover (high albedo).
The model is able to reproduce both positive and negative volume changes and validate our results with measured balances on different glaciers within the study area. Differences between measured and modelled balances reverse their sign in recent years with measured balances getting systematically more negative than the modelled ones. This is a result of a sequence of negative mass balance years and the related albedo-feedback. We therefore introduce a time-dependence of DDFs making it a four-dimensional variable in our study.
A statistical approach to iceberg calving: The role of disorder and the demise of deterministic predictability
Jeremy N. Bassis
Corresponding author: Jeremy N. Bassis — jbassis@umich.edu
Iceberg calving provides an efficient mechanism to transfer large amounts of ice to the ocean in a near instantaneous fashion. Previous attempts at formulating models of iceberg calving have focused on developing criteria that predict when an isolated crevasse can penetrate the entire ice thickness. In this study, I hypothesize that because the distribution of pre-existing flaws within the ice is unknown, the statistical nature of fracture must be considered. I propose a stochastic model of iceberg calving based on a combination of extreme value statistics and statistical-thermodynamics. In this theory, the probability of fracture and hence of iceberg calving is a function of the applied stress, ice thickness and fracture density. The fracture density is determined using a statistical-thermodynamic approach specifically developed for fracture of disordered media. Notably, the theory can be applied to both floating and grounded glaciers, calving can initiate from anywhere within (not just the terminus) and the model can incorporate additional environmental forcings (e.g., ocean swell induced flexure). I compare predictions of the model against observed steady-state floating ice tongue lengths and idealized outlet glacier configurations. A key prediction of this model is the existence of fluctuations in the position of calving fronts, stable or otherwise. These fluctuations can bump an otherwise healthy tidewater or outlet glacier into a phase of rapid retreat, leading to brief cycles of episodic retreat (and occasionally advance).
Results from the new glacier inventory for the Jostedalsbreen region, Norway, derived from Landsat TM scenes of 2006
Frank Paul, Liss Marie Andreassen
Corresponding author: Frank Paul — frank.paul@geo.uzh.ch
The last glacier inventory for southern Norway was compiled from aerial photography acquired in the 1970s. Field measurements of length changes at selected glaciers indicate strong and spatially heterogeneous fluctuations in the past decades. In order to get an overview on the overall changes, glacier extent have been mapped for mainland Norway from recent Landsat data in the framework of the project CryoClim. In this study we present the results of the new inventory derived for the Jostedalsbreen region and compare glacier extents to previous data sets from various sources. In principal, mapping of glacier extent from optical satellite data is straightforward in Norway, because only few glaciers are covered by debris. However, persistent cloud cover and large amounts of seasonal snow at the end of the ablation period delayed the acquisition of suitable satellite scenes from Landsat TM in this region for about two decades. Finally, two near perfect scenes were acquired on 16 September 2006, at the end of the most negative mass balance year on record in Norway.

Mapping glacier outlines from TM data was done using standard techniques (band ratio with threshold and manual editing). Topographic glacier inventory parameters were derived by DEM fusion within a GIS. The high quality national DEM and digitally available drainage divides helped to define glacier entities for the numerous icecap outlet glaciers in the region. Previous glacier extents were available from digitised topographic maps (1960s), the two previous inventories, and, for a part of the region, from a neighbouring Landsat TM scene acquired in 2003 that was analyzed previously. In addition, Landsat data from 1980 (MSS) and 1997 (TM) were used for calculation of length changes at selected glaciers.

The hypsographic analysis revealed the different typology of the glaciers, ranging from larger icecaps with several (valley type) outlet glaciers, smaller icecaps without outlets, mountain glaciers and abundant cirques. As expected, the glaciers show different responses to the recent climatic fluctuations. While the overall size changes of icecaps with outlet glaciers since the 1980s are small, icecaps without outlets and located at lower elevations show considerable shrinkage along their perimeter. Comparison with measured length changes show good overall agreement, but for some glaciers the changes are within the measurement uncertainty. Comparison with 2003 glacier extents in the Breheimen region indicate a recent strong acceleration of the shrinkage.
A new glacier inventory for the entire European Alps from Landsat TM scenes of 2003: Challenges and changes
Frank Paul, Holger Frey, Raymond Le Bris
Corresponding author: Frank Paul — frank.paul@geo.uzh.ch
For an accurate assessment of glacier changes at a regional scale, glacier inventories in a digital vector format are a basic requirement. Such data sets are currently derived from satellite imagery in the framework of the GLIMS initiative for nearly all parts of the world. For modelling of climate change impacts on glaciers as well as for change assessment, a consistent data set (e.g. acquired in the same year and processed with the same method) is particularly valuable. In some countries of the European Alps, new glacier inventories have been derived in the recent past from a variety of sensors and methods, including satellite data, aerial photography and laser scanning. In order to have a consistent inventory for all glaciers in the Alps freely available, we have created in the framework of the ESA project GlobGlacier a new glacier inventory from Landsat Thematic Mapper (TM) scenes acquired within two months in the late summer of 2003. Topographic attributes for each glacier are derived from the SRTM DEM and the entire data set will be integrated in the GLIMS glacier database.

After L1T corrected Landsat TM scenes were available for the entire Alps from the USGS archive, we converted them to glacier outlines using the standard methods (thresholding of ratio images, manual editing of debris-covered glaciers). Drainage divides for individual glaciers were derived from national DEMs if available or the SRTM DEM and inventory parameters were automatically extracted within a GIS. In total, ten TM scenes were processed and the outlines combined in one data set. Changes of individual glaciers were calculated in specific regions by a comparison with the inventories from the 1970s.

The 2003 inventory consist of 3800 glaciers larger than 0.01 kmsup2 covering 2030 kmsup2, an overall area reduction of about 30% compared to the 1970s glacier inventory. Several glaciers were excluded from the inventory as outlines could not be properly identified due to debris-cover and more than 50 smaller glaciers disappeared. The normalized size class distribution is very similar in all countries and mean elevation of individual glaciers does not show the typical dependence on aspect. However, a pronounced geographical pattern is found for mean elevation that is related to annual precipitation amount.
Seasonal evolution of water source contributions to the subglacial outflow from a land-terminating Greenland ice sheet outlet glacier: Insight from a new isotope mixing model
Maya Bhatia, Sarah Das, Elizabeth Kujawinski, Paul Henderson, Matthew Charette
Corresponding author: Maya Bhatia — mayab@mit.edu
Little is currently known about the subglacial hydrological system beneath the Greenland ice sheet (GrIS). Evidence that a large fraction of annual surface meltwater may drain to the bed of the GrIS suggests that portions of the GrIS subglacial hydrological system may undergo a seasonal evolution, akin to those present beneath alpine glaciers, with significant geophysical and biogeochemical implications. The interaction of surface meltwater with the glacier bed alters its chemical composition from dilute snow- and ice-melt to chemically-enriched subglacial discharge waters. In theory, variations in solute concentrations could be used to infer the evolution of the subglacial drainage network by differentiating water source contributions. There is ample evidence, however, that chemical mixing models which rely on bulk, non-conservative properties such as electrical conductivity, are unreliable. Here we present results from a novel multi-component isotope mixing model to quantify the relative contributions of surface snow, glacial ice melt, and basal melt to the bulk meltwater discharge at a small (~ 5 kmsup2) land-terminating outlet glacier along the western margin of the GrIS. This model utilizes radioactive and stable isotopes (sup7Be, sup222Rn, sup18O, D) as passive flow tracers coupled with stream discharge and meteorological measurements. Each of these tracers has a unique and predictable signal for the different source waters that ultimately contribute to the subglacial discharge. We also use the radioactive nature of sup7Be (half-life 53.3 d) to constrain the meltwater transit time from the glacier surface to the ice margin at the onset of the summer melt season. Finally, we compare our model results to those obtained from using conservative ionic species as tracers in order to assess the applicability of this approach for hydrograph separation. Results illustrate (1) the potential of using beryllium-7 (sup7Be) and radon-222 (sup222Rn) as tracers for snowmelt and basal melt, respectively and (2) that basal melt comprises a larger proportion of early season (May) discharge waters compared to peak season (July) waters. The development of an isotope mixing model that can successfully differentiate water source contributions would complement existing geophysical methods used to study seasonally evolving subglacial hydrological systems.
New monthly glacier mass-balance measurements on Glacier Conejeras, Nevado Santa Isabel, Colombia, provide insight into rapid glacier retreat
Jorge Luis Ceballos, Ignacio Meneses, Leonardo Real, Eduardo Tobon, Christian Huggel, Michael Zemp
Corresponding author: Jorge Luis Ceballos — jorgec@ideam.gov.co
Glaciers in Colombia are important indicators of climate change in tropical high-mountain areas at latitudes where few glaciers worldwide exist. In recent years the rapid retreat of Colombian glaciers has been documented in terms of area change. Most recent measurements indicate a total glacier area of 46.8 km2 in Colombia, with a 57% reduction compared to 1950. Currently, about 3% of glacier area is lost per year. However, little has been known so far on the relation between glacier retreat and climatic processes and changes due to lacking mass balance and high-altitude climate monitoring. Therefore, in 2006 a new mass balance measurement has been initiated on Conejeras Glacier on Santa Isabel Volcano in the Cordillera Central of Colombia. This glacier lies at 4°45’ northern latitude and extends between 4680 m and 4950 m asl.
Total mass balance between April 2006 and March 2010 is -6.4 m w.e., resulting in an average annual mass balance of -1.6 m w.e. Thanks to the high temporal resolution of the measurements, i.e. once per month, important insights into the response of Conejeras Glacier to climatic variations could be found. On the one side, the mass balance reflects the marked equatorial seasonality, and on the other side influence of moderate ENSO activity in 2006-2007 and 2009-2010. During these periods maximum loss was up to -0.92 m w.e. per month (February 2010). Continuous positive mass balance periods were monitored from June to December 2007, and May 2008 to April 2009 with maximum gain up to 0.31 m w.e. (September 2008). The equilibrium line altitude is fluctuating according to the monthly mass balance and often exceeds the maximum elevation of the glacier. Automatic weather stations mounted in the vicinity of the glaciers provide additional information to better understand climatic variations during the mass balance measurement period.
Extrapolation of current rapid retreat rates at glaciers in Colombia make an extinction within three to four decades a likely scenario. Related implications for ecosystems and socio-economic activities are currently investigated.
Assessing temperature and precipitation patterns from the EC-EARTH GCM over Greenland
Anne Munck Solgaard, Shuting Yang, Gudfinna Adalgeirsdottir, Christine Hvidberg
Corresponding author: Anne Munck Solgaard — solgaard@gfy.ku.dk
In this study we evaluate the performance of the global climate model EC-EARTH over Greenland by comparing modeled temperature and precipitation to observations as well as ERA-40/ERA-Interim data. A realistic surface mass balance forcing is essential when modeling the evolution of ice sheets and glaciers in the future as well as in the past. Mean monthly temperatures from the model for the period 1979-2008 are assessed by comparison with observations from GC-Net (Greenland Climate Network) automatic weather stations and DMI (Danish Meteorological Institute) coastal weather stations. A seasonal pattern is found in the difference between the model and the observations, but no spatial trend is detected. Annual and monthly mean precipitation rate output from EC-EARTH are also compared with accumulation maps based on observations as well as the monthly means from the DMI weather stations and ERA-40/ERA-Interim data for the same time period. In general, the model captures well the large scale patterns and seasonal variability, but it simulates higher precipitation rates in southeast Greenland compared with the ERA-40/ERA-Interim data and accumulation maps based on observations alone. Relationships between accumulation and temperature patterns and the large scale atmospheric circulation pattern are identified. This will help to guide the correction and downscaling of model output before it is applied as forcing of ice flow models
Observed Glacier Changes and Related Climate Trends in the Cusco Region, Southern Peruvian Andes
Salzmann Nadine, Huggel Christian, Rohrer Mario, Silverio Walter, Mark Bryan G., Hardy Douglas R.
Corresponding author: Salzmann Nadine — nadine.salzmann@geo.uzh.ch
In many regions worldwide, mountain glaciers are an important fresh water resource for the people living there and the adjacent lowlands. In the tropics, where distinctive wet-dry seasons govern the hydrological regime, glaciers are often the only fresh water source during the dry season. Although glacier retreat is observed worldwide, specific local long-term measurements and climate data are often scarce, particularly in tropical mountains. As a consequence, the processes that lead to major glacier retreats are not fully understood, and thus for future projection several uncertainties remain.

The vast majority of tropical glaciers on earth is located in the Peruvian Andes. While in the region of the Cordillera Blanca several glacier measurement and observation programs have been conducted during the past decades, in the Cusco region (Cordillera Vilcanota), the second major glaciated area in Peru, very little specific data is available so far.

Within a climate change and adaptation program jointly borne by the Peruvian and Swiss Governments, a first step is taken to collect and analyse available glacier and climate data for the Cordillera Vilcanota in order to improve process understanding of these high altitude tropical glaciers at the edge of the Amazon and the Central Andes. Based on Landsat TM satellite images, glacier outlines for 1985 (443km2), 1996 (343km2) and 2006 (296km2) were digitized and confirm the global observed trends of glacier surface reduction also for this tropical area. In an earlier study conducted by USGS, a Landsat MSS based glacier area value of 539 km2 is published for 1975. Moreover, we calculated estimates on volume changes to provide additional information towards a clearer picture on the ice mass loss during the past decades in the Cordillera Vilcanota. Within the aforementioned program, great efforts have also been put into climate station data treatment in the Cusco/Apurimac area. As a result, a relatively dense network of quality checked climate data is now available for the Cusco region, including several time series since 1965. Additionally, we consider in this study climate information as provided by the NCEP/NCAR Reanalysis, and include a verification analysis prior to their use, with five years of AWS data from the summit of Quelccaya Ice Cap (5,680 m). Time series analysis for air temperature, humidity and precipitation of the aforementioned datasets are then conducted in order to determine the extent to which these climate datasets explain the observed glacier retreat.

These basic analyses become particularly important for the area, because so far no data is available, although people living in the Cusco areas will suffer substantially in case of continuing glacier retreat. In order to plan adequate adaptation measures, basic data on regional climatic trends and its impacts on glaciers and other environmental systems are urgently needed.
The monitoring of calving glaciers near Zhongshan Station with satellite images and field survey
ZHOU Chunxia, E Dongchen, WANG Zemin, SUN Jiabing, AI Songtao, ZHOU Yu
Corresponding author: ZHOU Chunxia — zhoucx@whu.edu.cn
The calving and ice velocity of glaciers are in very close relationship with the global climate and indicators of the local effects of global changes. Spaceborne optical and SAR images are the main information sources for glacier monitoring, and field survey is valuable to identify the velocity from other methods. Polar Record Glacier is about 50 km to the west and Dalk Glacier is about 3km to the east of the Zhongshan Station, east Antarctica. An enormous tongue of ice has broken free from Polar Record Glacier creating an iceberg tongue more than 25 km long. Iceberg calving is the primary means by which ice accumulated on the interior of Antarctica is eventually lost to the sea. This paper presents the interest of using optical and SAR data to monitor the changes of the Polar Record Glacier, Dalk Glacier and the calving iceberg. The multi-temporal satellite data, including Landsat, ERS and Envisat, etc, cover from 1970s to now. Based on the geometric rectification, registration and overlay processing on different temporal remote sensing images, preliminary results are presented on information extraction from optical and radar remote sensing data, the measurement of glacier surface velocity and changing characteristics analysis. In addition, field surveys are taken in recent years for Dalk Glacier since it is not far away from the Zhongshan Station and the observation condition is tolerable. The velocities obtained from field survey are consistent with the value derived from the satellite data. Based on the analysis of multi-term velocity and dynamic characteristics, the prediction of the calving glacier and its calving iceberg are discussed.
Modelling melt plumes and calving in East Greenland
Martin EW O'Leary, Poul Christoffersen, Ruth I Mugford, Anthony Seale
Corresponding author: Martin EW O'Leary — mewo2@cam.ac.uk
In recent years, many authors have sought to link the large fluctuations in
ocean temperatures around Greenland with the retreat of tidewater glaciers
over the same period. One mechanism for this process which has been suggested
is the melting of the ice front by warm fjord water, and the subsequent
destabilization of the above-water portion of the glacier.

The dominant control on the melt rate at the ice front is the dynamics of the
frontal meltwater plume. We present results from a model of this melt plume,
based primarily on previous plume models which have been applied beneath ice
shelves. We show, using both model data and mathematical arguments that in the
case of a frontal melt plume, unlike in the ice shelf case, the dependence of
the melt rate on temperature is very close to linear.

Using hydrographic data from Kangerdlugssuaq Fjord from both 1993 and 2004,
we calculate summer melt rates which are similar to those which have been
measured by previous authors. We also use oceanographic data from General
Circulation Models to investigate seasonal variability in both the quantitative
and qualitative behaviour of the plume. We find that melt rates are relatively
stable under seasonal variations, although the qualitative behaviour of the
plume does vary noticeably.

Finally, we show a possible link between the annual cycling of this plume and
the regular clearing of the seasonal ice melange from the fjord - a process
which has been linked to a loss of buttressing pressure on the ice front, and
increased calving. We also compare this with a new dataset of frontal positions
from MODIS imagery, and investigate links with the general seasonal behaviour of
ice fronts in East Greenland.
The Changing Albedo of the Greenland Ice Sheet
Jessica M Human, Jason E Box
Corresponding author: Jessica M Human — human.2@osu.edu
Mass loss of the Greenland ice sheet has been a major scientific and societal issue due to potential impacts on rising sea level. The study evaluates Greenland ice sheet surface albedo sensitivity to surface melt intensity, precipitation, and air pollution using data from the MODIS and MOPITT sensors operating on the NASA Terra satellite for years 2000-2009. Precipitation rates are simulated by the Polar MM5 climate data assimilation model. Statistical regression facilitates ranking the relative importance of each of the albedo forcings in space and time. Quantitative estimates of the albedo sensitivity to its forcing factors are made over the observed inter-annual range. The work investigates regional patterns to quantify melt water production associated with absorbed solar radiation variability. In-situ records are used to evaluate the cloud radiative effect an important modulator of absorbed solar radiation and in turn for ice melt. Insights into Greenland ice sheet melt-precipitation-pollution-albedo feedback are presented, key in better understanding the mass balance response of the ice sheet to past, present, and future climates.
Mesoscale Climate controls on West Antarctic Ice Shelf Surface Melting
Chris Karmosky, Derrick Lampkin
Corresponding author: Chris Karmosky — cck146@psu.edu
Recent dramatic disintegration of the Larsen B Ice Shelf in 2002 and the partial collapse of the Wilkins Ice Shelf in 2008 and 2009 have prompted the urgent need to understand ice shelf dynamics. Results from models have suggested that collapsing ice shelves on the West Antarctic Ice Sheet (WAIS) are not a completely new phenomenon, as sporadic collapse and re-growth has occurred several times over the past million years. However, the collapse of large Antarctic ice shelves has the potential to increase sea level in the near-term significantly beyond anything experienced over the course of human history. This study makes use of a passive microwave melt record over Antarctic Ice Shelves, the Cross Polarized Gradient Ratio (XPGR) for assessing surface melt onset and duration for the 1987-88 through 2007-08 ablation seasons. Additionally, Self-Organizing Maps (SOMs), a neural networking approach to climate downscaling, are used to elucidate synoptic scale and mesoscale weather patterns that are associated with surface melting events. In order to assess these climate conditions leading to melt, SOMs will be forced by Polar MM5 output over the ERA-40 reanalysis time period for several variables, including 2m temperatures, vector winds, 500mb heights, as well as moisture variables representing latent heat flux. Identification of the synoptic-scale weather patterns can provide insight to the physical processes responsible for the generation and persistence of surface melt conditions over Antarctic ice shelves.
Parameterizing Greenland’s surface mass balance in the Parallel Ice Sheet Model (PISM)
Regine Hock, Jason Box, Ed Bueler, Constantine Khroulev
Corresponding author: Regine Hock — regine@gi.alaska.edu
The current version of the Parallel Ice Sheet Model (PISM) adopts simple parameterizations to simulate surface mass balance. Degree-days to represent melt intensity are computed as a function of latitude, longitude, and surface elevation. For present-day simulations accumulation rates are derived from output from high-resolution climate modeling. The purpose of this study is to improve the current melt model by deriving alternative formulations that more accurately reproduce the spatial variability of degree-day factors across the Greenland ice sheet. We use in-situ surface mass-balance and satellite-derived albedo and snow line observations in concert with output from the Polar MM5 regional climate model to enhance the current surface mass balance scheme. Comparisons between the previous and the new scheme are discussed.
Sensitivity of the frozen-melted basal boundary to perturbations of basal traction: Isunnguata Sermia, western Greenland
Douglas Brinkerhoff, Toby W. Meierbachtol, Jesse V. Johnson, Joel T. Harper
Corresponding author: Douglas Brinkerhoff — douglas.brinkerhoff@umconnect.umt.edu
A full-Stokes, thermo-mechanically coupled, numerical model is used to explore the interaction between basal thermal conditions and motion of a terrestrially terminating section of the west Greenland ice sheet. The model domain is a two-dimensional flow line profile extending from the ice divide to the margin. Modeled surface velocities are compared to interferometrically determined surface velocity data to find a basal traction field that closely matches observations. After applying perturbations to the empirically determined basal traction field of a steady state model configuration, 50 year long fully dynamical runs are executed. The hypothesis that changes in sliding speed produce a migration of the frozen to melted boundary (FMB) at the bed is tested by monitoring the basal thermal properties of model output using two metrics: 1) the position of the FMB, and 2) the distribution of basal melt water production. The position of the FMB is shown to be sensitive to perturbations to the basal traction field and prescribed geothermal heat flux. The coupling between FMB position and sliding velocity is, in some cases, dominated by the advection of cold ice from the ice sheet surface, rather than increased frictional heating associated with sliding.
Ice Sheets Velocities from MODIS data in Arctic/Antarctic regions
Yushin Ahn, Ian Howat, Jason Box
Corresponding author: Ian Howat — ihowat@gmail.com
Feature tracking between repeat satellite imagery greatly enhances our understanding of large-scale changes in ice dynamics and is a primary source for monitoring ice sheet mass balance. Additionally, when analyzed in time series, velocity changes directly indicate the pattern of motion and acceleration (or deceleration), which in turn are used to predict the future sea level rise. While Synthetic Aperture Radar Interferometery (InSAR) and speckle tracking for glaciers and ice sheets has been providing velocity field in Polar Regions, yet temporally sparse, large quantity of optical sensor imagery has drawn the attention for potential velocity source for glacier studies.

MODerate resolution Imaging Spectroradiometer (MODIS) on TERRA and AQUA satellite contains imagery with spatial resolution of 250 meter (bands 1 and2), however combining high temporal resolution and a decadal dataset still produces large set of pairs for ice sheet feature tracking. We first gather major ice sheets in Antarctica and whole Greenland MODIS data and develop MODIS data feature tracking method that stems from MIMC (Multiple Image/Multiple Chips) for high spatial resolution imagery. With proper time separation of pairs, preferably more than 2 years in 400meter/year velocity ice sheet, 1) inter-decadal velocity variation, and 2) velocity changes before/after large ice sheet breakups will be investigated.
Glacier recession and human vulnerability in the Cordillera Blanca, Peru
Bryan G. Mark, Jeffrey Bury, Jeffrey M. McKenzie, Michel Baraer, Adam French, Kyung In Huh, Sarah Fortner, Ricardo Jesus Gomez
Corresponding author: Bryan G. Mark — mark.9@osu.edu
Climate change is forcing dramatic glacier mass loss in the Cordillera Blanca, Peru, resulting in hydrologic transformations throughout the main Rio Santa watershed and increasing human vulnerability. We report on transdisciplinary collaborative research evaluating the complex relationships between coupled environmental and social change in the region. State-of-the-art measurements of glacier surface elevation and remaining ice depth quantify both late 20th century volume loss and remaining glacier storage. Integrated observations of water quality, quantity, human livelihoods and perceptions of change were collected in glacier tributary watersheds to the Rio Santa from 2004 to 2009. Hydrologic results suggest there has been an average increase in the specific discharge of the more glacier covered catchments (>20 percent glacier area) as a function of stream water changes in ionic chemistry and stable isotopes (δsup18O and δ2H), while a multi-decadal decreasing trend in discharge from the regional watershed suggests increased withdrawal. There is a large (mean 60 percent) component of groundwater in dry season discharge and wetland-stream dynamics may be critical to water quality and seasonal storage associated with tropical glacier retreat and seasonal rain cycles. A multivariate analysis identifies natural tracers among the hydrochemical and isotopic characteristics of sampled waters that depend more on water origins than on the valleys geophysical characteristics. Results highlight a key role for the peri and/or para glacial deposits in providing significant water volumes to surface water streams. Streams in the region are also threatened by the legacy of mining operations and a recent increase in new mineral extraction activities. Yet even glacial fed streams remote from mining activities feature elevated metal concentrations since retreating glaciers expose sulfide-rich rock outcrops that are susceptible to weathering by both air and water. Relative to specific runoff, high cation flux indicates high chemical weathering rates, while silicate flux is consistent with glacierized catchments globally. Finally, extensive key interviews and seventy-two randomly sampled household interviews within communities located in three case study watersheds demonstrate that a large majority of households perceive that glacier recession is proceeding very rapidly and that climate-change related impacts are affecting human vulnerability across multiple shifting vectors including access to water resources, agro-pastoral production, tourism and weather variability.
Influence of recent glacier changes in the Karakoram Himalaya region on the streamflow variability of the Upper Indus River
Bibi S Naz, Laura C Bowling, Moetasim Ashfaq, Noah S. Diffenbaugh
Corresponding author: Bibi S Naz — bnaz@purdue.edu
The absence of any long-term measurement program for climatic and glaciological variables due to the high cost involved and difficulties of working in the Karakoram Himalaya region is a major problem in evaluating the impact of glacier changes on the streamflow variability of river originating in this region. Given the difficulties involved in field surveys and the absence of long-term historical data, a combination of remotely sensed data and land surface hydrological modeling were used to assess the effect of glacial fluctuations on annual runoff discharge in the Upper Indus Basin (UIB). The change detection analysis of glacier zones including snow-covered ice, clean ice and debris-covered ice using historic Land Remote-Sensing Satellite (Landsat) images available for the years 1977, 1998 and 2006 combined with the glacier elevation difference estimation using the ICESat elevation data and the Shuttle Radar Topography Mission (SRTM) C-band digital elevation model for the period of 2004-2008 shows glacier expansion in this region. Similarly, a glacier mass balance estimated using the FVGCM-RegCM3 climate model output at 25 km resolution for the time period of 1961-1990 also shows a positive mass balance for the glaciers located at higher elevations. The impact of these glacier changes on streamflow variability was first examined through seasonal trend analysis of observed streamflow data from gauge stations in the UIB over the last 40 years of historic climate variability. The analysis of seasonal discharge trends shows decreasing summer streamflow for glacier-dominated watersheds, while increasing autumn, winter and spring streamflow trends were observed for snow-dominated watersheds. To further examine the effect of glacier and snow cover fluctuations on the downstream freshwater regime of the Indus River, the large scale Variable Infiltration Capacity (VIC) model, run using daily precipitation and temperature data from RegCM3 climate model was used. The VIC model was first modified to better represent ice accumulation, ablation and transport in alpine glacier systems. The glaciological component of the model was evaluated from point scale simulations at selected locations where glacier mass balance estimations are available from radar altimetry analysis. The model was then run at watershed scale to evaluate the streamflow forecast by comparing the predicted discharge to the observed historical river discharge. The results from this analysis provide an enhanced understanding of the influence of glacier fluctuations on the magnitude and timing of total annual discharge of major rivers in the UIB.
Joel Brown, Joel Harper
Corresponding author: Joel Brown — jbrown@cgiss.boisestate.edu
Georadar is used in the cold snow zone of ice sheets for extrapolating age/depth horizons over long distances between ice cores, effectively mapping the spatial variability of accumulation. Due to infiltration and refreezing of surface melt in the percolation area of the Greenland Ice Sheet, internal reflecting horizons in georadar data may not represent laterally continuous layers. We conducted 3D georadar grid surveys with high spatial resolution in conjunction with multiple 10 m firn cores to investigate the relationship between internal reflection horizons in the georadar data and stratigraphic horizons within firn cores. Data were collected at two sites in the percolation zone of the Greenland Ice Sheet: 1) Crawford Point, near the top of the percolation zone at 1997 m.a.s.l., where melt water infiltration and ice layer development is relatively minor. Here we conducted a 20 m x 20 m radar survey in conjunction with 8 firn cores to 10 m. 2) At ~1660 m, where surface melt is high and substantial ice layers develop due to melt water infiltration. Here we conducted a 17 m x 50 m georadar survey in conjunction with 2 firn cores to 10 m. The georadar data show a high degree of continuity over both grid sites and have identifiable internal reflection horizons at depths that may be consistent with annual accumulation. Georadar data also show large amounts of intra-layer variability that we attribute to small, discontinuous ice layers and ice pipes. The core data do not show laterally continuous ice layers or laterally traceable stratigraphy that would easily define annual layering. Because core data lack lateral continuity of firn stratigraphy, internal reflection horizons within the firn of the percolation zone most likely correlate with laterally consistent bulk changes in density. Further, because annual accumulation signals are not visually present in the cores, internal radar reflecting horizons cannot be assumed to represent annual layering in the percolation zone.
Field Measurement of Melt water Retention on the Greenland Ice Sheet
Joel Harper, Neil Humphrey, Joel Brown, Tad Pfeffer
Corresponding author: Joel Harper — joel@mso.umt.edu
Melt water retention in snow and firn of Greenland’s accumulation area plays an important role in the ice sheet’s mass balance. Here we present results from a field campaign focused on quantifying the magnitude and extent of meltwater infiltration and refreezing in western Greenland. During summers of 2007-2009 we collected multi-faceted data along a 90 km transect extending from 2000-1300 m elevation. We measured near-surface heat flow and firn stratigraphy/density at 17 intensive study sites spaced every 5-10 km along the transect . Heat flow was measured with 33 channel thermister strings extending to 10 m depth and logging year-round on a 30 min time base. Firn stratigraphy and density was measured in 24 ice cores 10 m deep, with 2 or more cores at each study site. Ground-based radar surveys imaged firn stratigraphy and characterized density to a depth of ~80 m from analysis of electromagnetic velocity. We find that from 2000-1625 m elevation surface melt is minimal and melt water infiltrates vertically to form thin ice layers. The density-depth profile is similar to that computed for dry firn using a common densification model. Between ~1625-1475 m elevation, strong surface melt infiltrates to fill about half of the available pore space of the upper 10 m. Infiltration has a high degree of spatial variability, with some water moving vertically and some water moving horizontally on top of decimeter to m thick ice layers . Melt water locally infiltrates to more than 10 m depth, and through more than a decade of accumulated firn. Below ~1475 m elevation, nearly all pore space is filled by infiltrated meltwater. Both our thermal and density measurements indicate that the runoff limit is above equilibrium line by a distance of about 30 km and about 300 m in elevation. These results have implications for modeling the mass balance and interpreting recent surface elevation changes of the Greenland Ice Sheet.
Spatial Analyses of Glacier Recession in the Cordilleras Apolobamba and Quimza Cruz in the Latter 20th Century
Joni L. Kincaid, Iliyana D. Dobreva, LaDonna R. Latterman, Andrew G. Klein
Corresponding author: Joni L. Kincaid — jkincaid@geog.tamu.edu
Monitoring changes in Andean glaciers is of utmost importance due to mounting concerns regarding water availability to major Andean cities. Observations of glacial change in the region which are critical to the prediction of future water supplies are incomplete because of the expense and logistical difficulty with field work. However, increases in the availability of remotely sensed images and advancements in remote sensing technologies coupled with a new generation of digital elevation models now provides the means for mapping the changes in glacier extent and possibly volume for many of the South American ranges, as well as for analyzing glacier areal change by elevation, aspect and slope. This research focuses on the outer tropical glaciers in the Cordilleras Apolobamba and Quimza Cruz (Tres Cruces) in the Bolivian and southern Peruvian Andes. It utilizes historical observations from the Peruvian and Bolivian Glacier Inventories dating back to 1965 and 1975, respectively, as well as Landsat Thematic Mapper images dating from 1986 to present and serves as an example of a methodology we are applying on other ranges in the region.
The glaciers in the Cordillera Apolobamba lost nearly half of their surface ice area over the period 1965-2000. The Cordillera Quimza Cruz glaciers lost over 43.4% (i.e, 28.04 kmsup2) of their area from 1975-2005. The most significant losses prior to the mid-1980s primarily affected small lower altitude glaciers many of which disappeared entirely. The greatest percentage loss in surface ice area occurred on glaciers with northwest and southeast aspects.
Spatial patterns of glacier change over these time periods are being compared to solar radiation analyses, temperature and precipitation trends derived from downscaling NCEP/NCAR reanalysis data and to the growing recent literature on climate change in the region to deduce glacier-climate relationships on these outer tropical glaciers.
Analysis of ice plains of Filchner/Ronne Ice Shelf using ICESat data
Kelly M. Brunt, Helen A. Fricker, Laurence Padman
Corresponding author: Kelly M. Brunt — kbrunt@ucsd.edu
We use laser altimeter data from the Ice, Cloud, and land Elevation Satellite (ICESat) to map the grounding zone of Filchner/Ronne Ice Shelf (FRIS), Antarctica. Ice flexure in the grounding zone occurs as the ice shelf responds to ocean height changes due primarily to tides. The landward and seaward limits of this flexure region, which define the grounding zone, can be detected through ICESat repeat-track analysis since each satellite pass is acquired at a different tidal phase. We have analysed all ICESat tracks across the FRIS grounding zone to produce a set of points corresponding to the limits of flexure and the break-in-slope associated with the grounding line. Comparison of our ICESat GZ estimates with previous estimates based on ground-based geophysical data or satellite imagery has revealed a number of ice plains, or regions of lightly-grounded ice. The main two ice plains we have identified occur east of Institute Ice Stream and west of Foundation Ice Stream. We present ICESat results for these two ice plains and discuss differences in the flexure characteristics across their GZs.
Dynamic Inland Propagation of Ice-thickness-Perturbations at ice Sheet Margins
Weili Wang, H. Jay Zwally, Jun Li
Corresponding author: Weili Wang — weili.wang@nasa.gov
Recent mass balance analysis of the Greenland ice sheet based on satellites ERS(92-02) and ICESat(03-07) observed surface elevation changes (dH/dt) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce the interior ice thinning at higher elevations. In this paper, we use a 3D numerical ice-sheet model that includes longitudinal stresses to investigate this upstream propagation. We use the ice-thickness changes (dHbd/dt) dynamic driven by ablation and ice dynamics that are derived from the observed dH/dt for the regions below 2000m of the Greenland ice sheet as perturbations to a 3D model in steady state. As defined, dHbd/dt is affected by both increased melting in the ablation zone and acceleration (or deceleration) of outlet glaciers. In model runs for 10-100 years, we found that extensive mass loss, represented by the changes in ice thickness below 2000 m around the ice sheet, does in fact cause interior thinning (or reduced thickening) on short time scales, e.g decadal. To quantify the impacts from different mechanisms that may affect the dynamic coupling, we also perform the tests using a high-order flow-line model. Results show that incorporation of horizontal-stress gradients in the model enhances the dynamic coupling rates by several percent. In the model, increase of the basal sliding also contributes to the thinning. The modeled thinning pattern over the ice sheet is in agreement with the observations showing enhanced inland thinning mainly occurs in west and east as well as the south-east regions of the ice sheet, while in the upper north and south-west parts the enhancement is least. We conclude that the interior ice response to the changes at the coast is more rapid than generally expected. Our results imply that satellite observed ice thinning (or reduced thickening) in the higher elevations of the ice sheet is likely induced by the extensive mass loss at the margins during recent years.
Partitioning of Ice Sheet Elevation and Mass Changes into Accumulation-Driven and Ablation/Dynamic-Driven Components
Jun Li, H. Jay Zwally
Corresponding author: Jun Li — jun.li@nasa.gov
Deriving the rate of mass change (dM/dt) from the altimetry measurements of surface elevation change (dH/dt) requires information on changes in both the recent accumulation rate A(t) and the surface temperature T(t) together with the knowledge of the bedrock motion (dB/dt). A method of estimating the mass change of the ice sheet using altimetry data combined with our unified firn densification model is presented. In our formulation, the surface elevation change dH/dt is due to the following components: the recent accumulation rate driven dHA/dt; the surface air temperature and accumulation rate driven compaction rates dCT/dt and dCA/dt; the ice dynamic imbalance dHd/dt with respect to the long-term accumulation rate together with the ablation-driven elevation dHb/dt, and the dB/dt. Our firn compaction model is used to calculate dCT/dt, dCA/dt, and dHA/dt using T(t) from AVHRR (1982-2008) monthly surface air temperatures and δA(t) equal to 5%/˚K. This allows calculation of the mass added (or lost) due to δA(t) over a given period, which along with dHA/dt gives the firn density ρA associated with the accumulation driven dHA/dt. The jointed dynamic and ablation term dHbd/dt is then solved according to the information of dH/dt. We show how this is applied to ICESat measurements of dH/dt in Antarctica to derive dM/dt and separate the accumulation-driven changes from the ice dynamic-driven changes.
Linking glacier change and water resource vulnerabilities in the tropical Andes: preliminary results from Chimborazo, Ecuador
Jeff La Frenierre
Corresponding author: Jeff La Frenierre — la-frenierre.1@osu.edu
Understanding the role of glaciers in buffering seasonal and annual variations in mountain hydrologic systems is of substantial importance for the sustainable management of water resources in a warming world. Increased glacial melting conditions have been documented worldwide, and the potential for increased water resource vulnerability on the part of downstream inhabitants has drawn attention in several areas, including the Himalaya and the Andes. In the tropical Andes, most of this work has been focused on glacierized watersheds in Peru and Bolivia, where strong precipitation seasonalities and relatively high glacial coverage occur. In Ecuador, glacial coverage is less extensive and seasonal variation in rainfall is less distinct, however numerous rivers nonetheless have their headwaters on the glaciers of the country’s multiple stratovolcanoes. The relationship between these glaciers and their local and regional hydrologic systems remains less well-understood.

Volcán Chimborazo (6268 m) features more than 10 kmsup2 of glacial coverage and forms the headwaters of four rivers that serve that serve the immediate domestic, irrigation and hydropower needs of over 200,000 people. This poster describes ongoing research that seeks to measure the extent and rate of glacier changes on Chimborazo, the relative contribution of glacier melt to stream and spring discharge, and the potential water resource vulnerabilities that may result for local inhabitants if glacier recession continues. First, an analysis of Landsat imagery estimates the amount of change in Chimborazo’s glacier coverage between September 1987 and September 2009. Second, samples from stream, spring and glacier sites (n = 58) were synoptically sampled within each of four watersheds during a 2010 drought period and analyzed for stable water isotopes. Variations in the isotopic characteristics of these waters with downstream travel away from the glacier input source within a given watershed are described, as well as variations between the different watersheds that may be the result of different amounts of glacier coverage and distinct local variations in climatic conditions. Finally, recent human infrastructural adaptations to diminished surface water availability are reported and discussed.
Antarctic Ice Sheet Mass Balance: Distribution of Rates of Mass Change for 2003-2008 versus 1992-2002
H. Jay Zwally, Anita C. Brenner, Matthew A. Beckley, Helen G. Cornejo, Mario B. Giovinetto, Jun Li, John Robbins, Jack L. Saba, Weili Wang
Corresponding author: H. Jay Zwally — zwally@icesat2.gsfc.nasa.gov
The mass balance of the Antarctic ice sheet is derived from surface elevation changes (dH/dt) measured by ICESat laser altimetry for the period from Fall 2003 to Fall 2008. The rates of mass loss and gain by drainage system (DS) are compared to those derived from ERS radar altimetry for the period 1992 to 2002. Our firn-compaction model is used to account for elevation changes driven by temporal variations in accumulation rates, as well as temperature, and to determine the appropriate density for converting measured volume changes to mass changes. Changes are partitioned into those caused by decadal-scale changes in accumulation rate and those caused by ice dynamics. Rates of mass loss from parts of the Antarctic Peninsula and West Antarctica appear to have increased since the 1990's, but other parts appear to be losing at smaller rates or gaining at larger rates. In West Antarctica, increased losses of 47 Gt/yr in three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) are nearly balanced by gains of 43 Gt/yr around the base of Peninsula and in the DS of ice streams C, D, & E. In East Antarctica, increased gains of 107 Gt/yr in about seven DS are only partially balanced by increased losses of 55 Gt/yr in six other DS. Overall, increases in mass in some regions, perhaps from increases in precipitation, are counterbalancing greater decreases in other regions, perhaps from ice dynamic changes. In the latter period, the northern part of the Antarctic Peninsula was losing about 25 Gt/yr, the base of the Peninsula and West Antractica were losing about 51 Gt/yr, and East Antarctica was gaining about 68 Gt/yr. Therefore, in approximately ten years, the Antarctic grounded ice has changed from losing about 50 Gt/yr to a state of near-balance.
The triggering of sub-glacial lake drainage during rapid glacier drawdown: Crane Glacier, Antarctica
Ted A. Scambos, Etienne Berthier, Christopher A. Shuman
Corresponding author: Ted A. Scambos — teds@nsidc.org
Ice surface altimetry from ICESat-1 and NASA aircraft overflights
spanning 2002 to 2009 indicate that a region of the lower Crane Glacier shows an unusual pattern of elevation loss, with a period of very rapid drawdown (~60 masup-1 between September 2004 and September 2005) bounded by
periods of more moderate rates (~25 msasup-1 until September 2004; ~12 masup-1 after September 2005). Using satellite stereo-image DEM differencing, we have determined that the region of increased drawdown is isolated in space as well as time (2.6 km along-flow by 1.2 km across-flow). The isolated feature is not seen in later DEM differencing. Moreover, a
series of formerly sub-glacial lake basins have been exposed by Crane Glacier's recent retreat. Our conclusion is that this feature represents a sub-glacial water body beneath the glacier that drained during the glacier retreat. Airborne ice penetrating radar data to date is unable to accurately map the basal ice surface. Examining the along-flow slope changes using airborne laser altimetry shows that the mean along-flow slope over the lake increased prior to the draw-down event, from 0.018 (+/-0.002) in November 2002 to 0.038 (+/- 0.002) in November 2004 . This slope change has significant implications for the pressure or geometry of a sub-ice water cavity. Given ice thicknesses (based on bathymetry of the ice front) of over 1200 m, it is unlikely that the cavity is in full hydrostatic equilibrium with the overlying ice. We infer that the drainage event was caused by hydraulic fracture of ice or hydraulic forcing of water flow up and over a downstream obstruction to drainage. A significant increase in glacier speed was observed in the vicinity of the drainage event during the period of lake drainage and afterward, from 400 masup-1 to over 1400 masup-1. This process of small sub-glacial water pockets being forced into the broader sub-glacial drainage system during glacier retreat may be an important feed-back on mass balance change for outlet glaciers.
Contributions of Cryosphere to Present-day Sea-Level Rise
C.K. Shum, Junyi Guo, Ian Howat, Hyongki Li, Jianbin Duan, Chunyen Kuo
Corresponding author: C.K. Shum — ckshum@osu.edu
The global sea-level is observed to be rising at a rate of 1.8–2.2 mm/yr during 1900–2009, which is an accelerated rate relative to the rate of ~0.1 mm/yr during the previous four centuries, 1500–1900. Ice sheets are thought to be the largest fresh water reservoirs on Earth and are the dominant sources contributing to present-day sea-level rise. There exists evidence of accelerated thinning of the margins of the Greenland and West Antarctic ice sheets over the past decade, presumably due to anthropogenic warming. However, recently published estimates of the recent contribution of mountain glaciers and ice caps to present-day sea-level rise are by far the largest and with a wide range: 0.52–1.4 mm/yr. The upper bound of this estimate represent ~78% of the observed 20th century and present-day sea-level rise. The current estimates of Antarctica’s and Greenland’s contribution to sea-level rise also have a wide range: –0.12 to +0.40 mm/yr, and –0.03 to +0.63 mm/yr, respectively. This study provides an estimate of the ice-sheet and glacier contributions to present-day sea-level rise using contemporary satellite measurements including satellite altimetry, GRACE, other data sets, and with an attempt to narrow the uncertainty between observations and geophysical predictions.
The role of Hudson Strait outlet in Younger Dryas sedimentation in the Labrador Sea
Harunur Rashid, David JW Piper, Mary Smith, Emily England
Corresponding author: Harunur Rashid — rashid.29@osu.edu
In the Younger Dryas (YD) the circum-North Atlantic region returned to near glacial conditions, widely attributed to the release of freshwater from the Laurentide Ice Sheet (LIS). The Hudson Strait was a major outlet for freshwater, icebergs and sediment from the LIS, that deposited Heinrich layers throughout the North Atlantic. Heinrich layer 0 (H0), the YD equivalent ice-rafting event, has been reported to be absent in deep water seaward of the mouth of Hudson Strait. We have identified meter-thick H0 carbonate-rich sediments of YD age seaward of Hudson Strait as nepheloid-flow deposits and as turbidites on the northeast Sohm Abyssal Plain. Otherwise, H0 is generally absent in cores from the Labrador basin. The thick proximal H0 bed indicates an important supply of freshwater through the Hudson Strait outlet of the LIS during the YD. The sparse distal sediment distribution and small depleted values in the planktonic foraminiferal δ18O in the Labrador Sea compared with H1 were probably the result of the position of the ice-margin, duration of freshwater discharge and dilution of freshwater signature with the ambient seawater during H0. This change is interpreted to result from the retreat of ice-margin towards land compared to H1 period at the mouth of Hudson Strait, resulting in different styles of sediment and freshwater transport between the H0 and earlier Heinrich events.
The GLIMS Glacier Database: Status and Analysis
Raup, B.H., Armstrong, R., Khalsa, S.J.S., Racoviteanu, A.
Corresponding author: Raup, B.H. — braup@nsidc.org
The Global Land Ice Measurements from Space (GLIMS) initiative has built a database of glacier outlines and related attributes, derived primarily from satellite imagery, such as from ASTER and Landsat, and the number of glaciers represented there continues to grow. Each snapshot of a glacier is from a specific time, and the database is designed to store multiple snapshots representative of different times.

As of April 2010, the database contains outlines for approximately 84 000 glaciers, covering 268 000 km2. Many more datasets are expected soon, such as from GlobGlacier, and the Regional Centers for Canada, Alaska, Argentina, Nepal, France, China, and others. Though the database does not yet cover the world's glaciers completely, approximate 550 glaciers have outlines from more than one time. This database enables analysis of global and regional glacier area and its distribution, glacier change, distribution of glaciers by classification, among many other possibilities.

This contribution reports the status of the GLIMS Glacier Database. In addition, we present early results from an analysis that combines glacier outlines with terrain elevation data in order to investigate possible scenarios for glacier mass loss with rising modeled regional equilibrium line altitudes.
Present and future states of Himalaya and Karakoram glaciers
J. Graham Cogley
Corresponding author: J. Graham Cogley — gcogley@trentu.ca
A composite glacier inventory of the Himalaya and Karakoram has been created by merging records from the Chinese Glacier Inventory (CGI), several regional inventories produced by the International Centre for Integrated Mountain Development (ICIMOD), Kathmandu, and partial inventories from the Geological Survey of India. The only gap remaining once these sources are combined, the Indian part of Kashmir, has been filled by a reconnaissance inventory based on Soviet military maps at 1:200 000 scale drawn from satellite imagery of the 1970s and early 1980s. The Soviet maps, on which the contour interval is coarse (80 m), are supplemented with hypsometric data from the Shuttle Radar Topography Mission (SRTM) of February 2000. The reconnaissance inventory of Kashmir is georeferenced to the WGS84 datum, with horizontal accuracies of 20 to 50 m varying from map to map. Hypsometric curves from the SRTM data, with 100-m vertical resolution, are therefore reliable on a glacier-by-glacier basis. Georeferencing of the CGI and ICIMOD glacier outlines is typically much less good, and for topographic information from these sources it is necessary to fall back on the recorded minimum and maximum glacier elevations.

The newly complete inventory is time-transgressive and not suitable for glacier-by-glacier study of changes. It nevertheless serves well for a variety of large-scale analyses built up from single-glacier attributes. These include: the first reliable estimates of total glacier area, and of glacier volume by volume-area scaling; somewhat more uncertain estimates of total area as a function of time, derived with the help of a compilation of measured shrinkage rates; maps of glacierized area on a 5-arc-minute (~10 km) grid; improved maps of the mid-range altitude, an objective proxy for the equilibrium line altitude; and maps of temperature at the mid-range altitude from large-scale atmospheric reanalyses. These analyses, and the limited information on hypsometry, provide initial conditions for temperature-index modelling of mass balance. The quality of model estimates will be illustrated in comparisons with in-situ and remote-sensing measurements of mass balance, and prospects for regional projections of the evolution of Himalaya and Karakoram glaciers under standard forcing scenarios will be assessed.

Outside North America, the largest gaps in the World Glacier Inventory are now in Afghanistan (~500 square km inventoried of a total of 2 000 to 4 000 square km) and Mongolia (approximate glacierized area 600 square km). Lesser gaps, each of 25 square km or less, are in Turkey, Burma and northeastern Siberia.
Understanding Environmental Controls on Calving Events in Greenland
Kristin Schild, Gordon Hamilton, Leigh Stearns
Corresponding author: Gordon Hamilton — gordon.hamilton@maine.edu
The contribution of continental ice sheets to sea level rise has doubled in the last decade and the rapid acceleration of Greenland’s outlet glaciers has been one of the dominant factors in this contribution. The largest changes in speed have been observed at the tidewater margins of these glaciers, implying a link between terminus position and glacier dynamics. By understanding the controls on terminus position, we will be better able to predict future ice dynamic changes and ice sheet contributions to sea level. We are using high-temporal resolution satellite imagery to quantify interannual and intraseasonal variability in the timing of large calving events at outlet glaciers in Greenland. The role of environmental conditions in governing the observed variability is being examined using datasets of air temperatures and sea surface temperatures for regions encompassing each outlet glacier. Results show that Greenland outlet glaciers typically undergo a seasonal pattern of summertime retreat and wintertime advance. The onset of retreat varies from early-May through early-July, with no clear latitudinal pattern in timing. Several glaciers in our sample population (e.g., Helheim, Kangerdlugssuaq) show a substantial increase in intraseasonal variability following the onset of large changes in ice dynamics. We will discuss these results in conjunction with simultaneous observations of ice velocity, tidal stage and teleseismic activity.
Recent ice volume changes of the Kilimanjaro Ice Cap and Qori Kalis glacier (Southern Peru) using automatic DEM extraction
Roberto Filippi, Y. Ahn, H. Brecher, L. G. Thompson, B. Mark, P. Burns, P. Gabrielli, Kyung-In Huh, M. Lanzinger
Corresponding author: Roberto Filippi — robertofilippi82@gmail.com
The tropical Ice Cap of Kilimanjaro (5895 m a.s.l., Tanzania) and the Qori Kalis glacier (the main outlet glacier from the Quelccaya Ice Cap, 5670 m a.s.l., Southern Peru) retreated drammatically during the last century. Using a combination of aerial and terrestrial analytical photogrammetry several glaciological studies were conducted in order to reconstruct the aerial extent of these ice bodies and their linked change in volume. Until now the comparison of multi temporal Digital Elevation Models (DEM) derived using traditional analytical photogrammetry of these glaciers allowed the monitoring of the ice volume changes from year to year by analyzing the variations in elevation. In order to further constrain areal and volume changes of these two glaciers, new stereo terrestrial images of the Qori Kalis glacier were taken during the 2009 field campaign and new stereo aerial images of the Kilimanjaro ice cap were acquired in February 2010. We use these images to reconstruct orthoimages and to extract the automated DEM by using the digital photogrammetry workstation Leica Geosystems’ photogrammetry suite LPS 10, integrated to the software Erdas Image 10. The aim of this study is twofold: firstly we investigate the advantages and limitations of using automatic DEM extraction over human-operated traditional analytical DEM extraction method in rugged mountain area. After validating the DEM accuracy by manual 3D editing and digitizing, we compared our model with the last DEMs available (Kilimanjaro of 2007 and Qori Kalis of 2007) and we estimate the ice volume changes by using GIS analysis.
Abrupt Bølling-Allerød warming and Younger Dryas cooling recorded in lake sediments from the northern tropical Venezuelan Andes
Nathan D. Stansell, Mark B. Abbott, Valenti Rull, Donald T. Rodbell, Maximiliano Bezada, Encarni
Corresponding author: Nathan D. Stansell — stansell.9@osu.edu
A radiocarbon dated sediment record from Laguna de Los Anteojos, a cirque lake in the Mérida Andes of Venezuela, indicates that warmer and wetter atmospheric conditions occurred in the northern tropics at the onset of the Bølling (~14,600 to 14,100 cal yr BP), and warmer and drier conditions around the time of the Allerød (~13,900 to 12,850 cal yr BP). Geochemical and clastic sediment analyses from Los Anteojos show that glaciers then advanced at ~12,850 cal yr BP, reached their YD maximum extent at ~12,650 cal yr BP, and retreated until complete deglaciation of the watershed at ~11,750 cal yr BP. The onset of warmer conditions that ended the coldest phase of the YD occurred several hundred years earlier at Los Anteojos than in the high latitudes of the Northern Hemisphere. During the peak YD glacial advance, glacier equilibrium-line altitudes in the region were ~360 to 480 m lower, and temperature was ~2.2 to 2.9°C colder than modern. Independent palynological evidence from the Los Anteojos sediment core indicates that the northern Andes were more arid and at least 2.3°C colder during the YD. The direction and timing of glacial fluctuations in Venezuela is consistent with observations of marine sediment records from the Cariaco Basin that suggest abrupt cooling occurred at ~12,850 cal yr BP, followed by a shift to higher temperature after ~12,300 cal yr BP. The timing and pattern of climatic changes in northern South America is also consistent with paleoclimate records from the southern Tropical Andes that suggest a southward shift in the position of the Intertropical Convergence Zone occurred at the start of the cooling event, followed by a return to wetter conditions in northern South America during the late stages of the YD. The early warming of the tropical atmosphere and invigoration of the hydrologic cycle likely contributed to the shift to increased temperatures in the higher latitudes of the Northern Hemisphere at the end of the late glacial stage.
Assessing the volume and hypsometric changes of the Queshque glaciers in the Tropical Peruvian Andes
Kyung In Huh, Bryan G Mark
Corresponding author: Kyung In Huh — huh.26@osu.edu
Tropical glaciers are very sensitive to changes in climate due to the low latitude radiation regime and steep vertical mass balance gradients. These mountain glaciers have rapidly retreated over the 20th century, raising concerns about downstream regional water supplies under continued global climate change. Monitoring tropical glaciers using remotely sensed data has drawn a great attention in physical geography and earth science communities for decades and time-lapse analysis of sensory data has provided important variability information of tropical glacier recession. The motivation of this study is to refine a surface area to volume relationship for tropical glaciers to enable extrapolation of more detailed inventory of glacier volume and water resources. This study focuses on the Queshque glaciers in the Cordillera Blanca in Peru, within the world’s largest concentration of tropical glaciers, to assess the volume and topographic changes over the late 20th century using a combination of airborne and satellite remote sensing, digital photogrammetry and geospatial techniques. High resolution LiDAR (Light Detection and Range) data achieved in 2008 and DEM (Digital Elevation Model) from vertical aerial photographs taken in 1962 by stereo-photogrammetry are used to achieve estimation of modern equilibrium line altitudes (ELAs) as well as volumetric paleoglacier reconstruction. Multispectral ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) imagery taken during 2001 - 2008 reveal both current glacial surface topography and glacial profiles 46 years back, enabling calculation of the total volume loss trend over the last 46 years. The resulting improved understanding of how tropical glacier mass changes in response to climate dynamics is critical for global climate modeling, which can reliably predict future glacier changes only after accurately simulating the past.
High resolution, long term reconstruction of surface evolution in northwestern Greenland for investigating dynamic glacier behavior
Greg Babonis, Bea Csatho, Toni Schenk, Cornelis van der Veen
Corresponding author: Greg Babonis — gbabonis@buffalo.edu
Over the past two decades we have seen dramatic changes in the behavior of Greenland Ice Sheet (GrIS) outlet glaciers. The trend of GrIS mass balance over the last decade shows acceleration in ice-mass loss resulting in increasing sea level rise greater than model predictions. Moreover, the mass loss has been rapidly spreading toward higher latitudes and elevations, in particular along the northwestern coast. Although recent changes of outlet glaciers, including thinning, flow acceleration, and calving front retreat are well documented, the physical processes driving these changes are not well understood. In order to better understand the mechanisms initiating these changes, it is important to extend the observational record to investigate the long-term thinning and retreat of GrIS, as well as the larger spatial pattern of changes that have occurred since the Little Ice Age and during subsequent warm periods (1902-1910, 1930-1950).

This study will present a reconstruction of surface evolution within the northwest sector of the GrIS, between Upernavik and Thule, from the LIA to the present, combining data from topographic maps, stereo aerial photography, satellite imagery, and airborne and satellite altimetry measurements. The aim of this study is to develop the history of this region and constrain potential mechanisms responsible for the accelerated widespread marginal retreat and thinning observed in recent years. An outlet glacier recession history will be compiled by digitizing the extent of glaciers from topographic maps, satellite imagery, and aerial photography. Trimline reconstruction, stereo imagery and altimetry data will be used to investigate thickness changes. Additionally, ice penetrating radar sounding data will be used to develop an improved subglacial topography map to investigate the relationship between bedrock morphology and dynamic behavior. We will compare changes in the ice-mass loss pattern over time and the propagation of outlet glacier thinning to higher elevations, with climate records of both ocean and surface temperatures. Additionally we seek to estimate the potential contribution of the northwestern sector of the GrIS to sea level rise. This will be a benchmark for future studies, which will look more comprehensively at individual mechanisms.
An algorithm for detecting Greenland snowline changes using MODIS
Russell Benson, Jason Box
Corresponding author: Jason Box — jbox.greenland@googlemail.com
Each year at the end of the melt season, the maximum altitude where winter snow survives is a convenient and useful indicator of the combined effects of melting and snow accumulation. As such, snowline is an excellent holistic variable to indicate a glacier’s health. We use NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) optical satellite imagery to classify Greenland ice sheet snowline using reflectance and albedo thresholds and iterative supervised statistical modeling. Seasonally averaged MOD10A1 daily albedo data are used in conjunction with MOD09 imagery to detect snowline variations along the east and west slopes of the ice sheet for the period 2001-2009. Snowline measurements from the K-transect are used in algorithm tuning. Varying algorithm parameters are applied to both eastern and western slopes to account for differing terrain and the narrow east Greenland ablation zone. The sensitivity of the algorithm to thresholds and assumptions are evaluated to understand what is the smallest resolvable change.
Field observations of Subglacial Processes: From the meter scales to hundred kilometer scale
J. Paul Winberry
Corresponding author: J. Paul Winberry — winberry@geology.cwu.edu
Discharge from Earth’s large ice sheets is dominated by ice streams and outlet glaciers. Basal motion, either sliding or till deformation, often accounts for greater than 90 percent of an ice stream’s velocity. However, recent observations have shown that the physical conditions that permit this rapid motion are transient in both space and time. Understanding how the mechanisms that enable fast glacier motion vary over spatial scales is fundamental to our ability to prescribe the appropriate boundary conditions that will enable us to develop models to predict both future and past ice sheet changes. We will present observations that elucidate subglacial processes at both the large scale, greater than 100s of kilometers, and small scale, less than 10 meters. In particular, we will compare observations of the stick-slip motion of the lower 150 km of Whillans Ice Stream with passive seismic observations of small-scale (< 10 m) stick-slip that occurs on MacAyeal Ice Stream. We will show that the temporal pattern of deformation in each location suggests that the physical processes that control the motion of ice streams is similar over a wide range of spatial scales.
Nathan Amador, Derrick Lampkin, Byron Parizek, Katy Farness, Kenneth Jezek
Corresponding author: Nathan Amador — glacierguynate@gmail.com
Supra-glacial melt lakes are an important component of the Greenland ice sheet hydraulic system as they act as a water reservoir. Surface melt water production results in episodic drainage of supra-glacial lakes through a network of en-glacial channels or moulins. Previous efforts have focused on lake features that do not contribute water directly into regions of fast flowing ice. We investigate regions along the shear margins of Jakobshavn Isbrae, which are occupied by persistent, localized basins that are heavily crevassed and periodically inundated. We call these regions ‘saturated crevasses’ and have documented ~9.23 x 10-3 km3 of water drained from the largest assemblage of saturated crevasses on the northern flanks of Jakobshavn between July 8 and July 24, 2007. This was accompanied by local estimates of strain rates on the order of ~0.025 d-1. A 1-D finite element flowline model was used to evaluate the impact of drainage from these saturated crevasses on ice discharge into the main trunk of Jakobshavn. Results indicate that drainage from these features can enhance discharge amounts, through localized thinning and increase in velocity. Drainage effects on discharge are highly dependent on residence time of infiltrated melt water in sub-glacial environment.
Modeling the Evolution of Surface Ablation Features
L. MacLagan Cathles, Dorian Abbot, Douglas MacAyeal
Corresponding author: L. MacLagan Cathles — mcathles@uchicago.edu
Satellite derived observations show that both the duration and areal extent of melting in greenland is increasing. As the melting zone expands, understanding processes which affect melt rates becomes increasingly important. We show that small scale geometric surface features can trap significant fractions of insolation, increasing absorption by up to 40 percent. This enhanced absorption increases local meltwater production, which we suggest is an important process in creating available liquid water on the surface of an ice sheet. The coalescence of available liquid water in surface lakes effects the local surface albedo, and has been shown to play an essential role in establishing hydrological connections between the supraglacial and subglacial environments.

We developed a numerical model to explore the interaction between solar radiation and surface topography relevant to surface meltwater drainage, storage and transport. Model results reveal that simple idealized geometric surface features evolve into complex features resembling those observed on the surface of Greenland. Geometric surface features ablate in a manner that, over time, increases the feature’s effective albedo. However, features also widen as they evolve. This means that some features decrease the net effective albedo of the surrounding as they expand, further enhancing melt rates. We explore these feedbacks and their roll in the formation of available liquid water on the surface of an ice sheet, and attempt to describe simple rules-of-thumb that can account for these feedbacks in larger-scale models that cannot explicitly resolve them.
Derrick Lampkin, Justin Vanderberg
Corresponding author: Derrick Lampkin — djl22@psu.edu
Rapid draining through cracks beneath lakes has been characterized as a hydro-fracture process and has been implicated in transporting large volumes of surface melt water to the base of the ice sheet. It has been observed that numerous surface streams run between lakes that develop through out the summer. Many of the streams appear to terminate in large crevasse fields. An initial estimate of the total volume of surface melt water partitioned into surface flow through supra-glacial channels was derived for the 2007 melt season. Stream channel discharge capacity for a single lake was determined for lake drainage of ~4.81 x 10sup6 msup3 between July 8 and 24, 2007. This approach was applied to several stream channels, delineated from high resolution Landsat imagery and regional estimates of discharge was evaluated over the entire melt season.
Debris and sediment flux to grounding zones and glacial stability
Ross D. Powell
Corresponding author: Ross D. Powell — ross@geol.niu.edu
Since the earliest 20th century grounding-line depositional systems have been used to infer ice dynamics and glacial history from glacimarine systems. More recent process studies combined with new marine landsystem data and extended stratigraphic records from long geological cores, are refining our understanding of these systems and how they may be used in paleo-glaciological inferences of past ice sheet dynamics, regimes and history. Furthermore, although still too few, newer models are attempting to integrate ice flow with sedimentary processes and fluxes to better constrain ice dynamics. These newer data and models will be summarized and used to discuss past and future ice sheet dynamics. More observations and data are required from modern grounding zones to test the models and to provide cleared understanding of how to interpret older deposits - the libraries of past grounding-line behavior.
Glacial Retreat and Its Impact on Hydrological Processes on the Third Pole
Tandong Yao
Corresponding author: Tandong Yao — tdyao@itpcas.ac.cn
Glacial retreat with negative glacial mass balance on the Third Pole is characteristic since the 1960s and intensified in the past 10 years. The magnitude of glacial retreat is relatively small in the interior of the Third Pole and increases to the margins, with the greatest retreat in the Himalayas. The glacial retreat has caused an increase of more than 6 % in river runoff in the region. In some rivers, such as the Tarim River basin, the increase in river runoff is greater. The glacial retreat has also caused lake level rising in the lake basin with large coverage of glaciers such as the Nam Co Lake and Selin Co Lake basins, which cause Glacial Lake Expansion Flood (GLEF) and devastate grassland and villages near the lakes. Some glacial lakes at glacial terminus will cause more frequent Glacial Lake Outburst Flood (GLOF).
Abrupt climate change recorded in the Malan ice core on the Tibetan Plateau and its response to the ENSO and Pacific Decadal Oscillation
Youqing Wang, Tandong Yao
Corresponding author: Youqing Wang — yqwang@itpcas.ac.cn
Annual δ18O record in the Malan ice core from the northern Tibetan Plateau displayed climate variability from 1887 to 1998, with a rapid warming tendency throughout the period, a singular cooling in the period of 1990s, and an abrupt climate phase change happened about 1933. The comparison of it with the ENSO indices such as the Southern Oscillation index (SOI), the multivariable ENSO index (MEI), Niño 3 and 3.4 regional sea surface temperatures (SST), and the Pacific Decadal Oscillation (PDO) index, suggests that the El Niño events have more significant influence on the climate change recorded in the Malan ice core than that of the La Niña events. Statistical analysis indicated that the annual mean δ18O record significant positively correlated with the SOI (R=0.675) and negatively correlated with the MEI, Niño 3 and 3.4 SSTs (R= -0.725, -0.518 and -0.536, respectively) since 1950. However, the relationship between the δ18O and SOI was very weak in the whole period of 1887~1998, but the relationship between the δ18O and the PDO index was right significant. The contribution was mainly due to that the SOI dominates annual variability, the δ18O record and PDO index with obviously decadal climate variability. Then we inferred that the climate change recorded in the Malan ice core was strongly influenced by the ENSO on interannual timescale, on the decadal timescale which was modulated by the PDO.
Flow dynamics and mass balance estimates of four large East Antarctic outlet glaciers
Leigh A. Stearns
Corresponding author: Leigh A. Stearns — stearns@ku.edu
The East Antarctic Ice Sheet is Earth’s largest source of freshwater and has the potential to raise sea level by ~50 m. A significant amount of the ice sheet’s mass is discharged by outlet glaciers draining through the Transantarctic Mountains, the balance characteristics and dynamics of which are largely unknown. Here we examine the dynamics and mass balance of four large East Antarctic outlet glaciers. Together, these glaciers drain ∼1,500,000 kmsup2, or 12% by area of the entire Antarctic Ice Sheet. We quantify changes in ice velocity, surface elevation and mass balance to assess their stability, and examine force balance characteristics to understand the controls on their flow.

Mass balance is estimated using the input-output approach wherein we compare catchment-wide accumulation from three different sources with discharge fluxes based on satellite-derived surface velocity fields. These calculations show modest imbalances for some glaciers, and a large positive balance for Byrd Glacier, which is inconsistent with the recently observed subglacial-flood induced speed-up. Instead, we argue that catchment-wide estimates of accumulation rate contain large errors. In this study, we quantify the accumulation errors, explore some of their causes, and discuss their importance for our understanding of Antarctica’s climate and mass balance.
Impacts of temperature fluctuations in the Norwegian Sea on glacier mass balance in southern Norway
Marie Porter, Toby Sherwin, Brice Rea, Douglas Mair
Corresponding author: Marie Porter — marie.porter@sams.ac.uk
As the northern branch of the Atlantic Meridional Overturning Circulation cools at high latitudes it releases heat to the atmosphere. This release of heat helps to maintain the warm climate that is seen throughout Western Europe indicating coupling between the ocean and the atmosphere. The link between the oceans and atmosphere suggests that local changes in the Nordic Seas, to the west of Norway, may influence the mass balance of glaciers by more than just large scale atmospheric circulation.

The link between conditions in the Nordic Seas and glacier mass balance in southern Norway has been investigated using available long term measurements from the ocean and glaciers. Water temperature averaged over the top 15m of the water column at Ocean Weather Ship Mike (66N 02E) provided data for the (mixed) sea surface temperature (MSST) in the southern Nordic Seas over a 50 year time series. Summer, winter and net surface mass balances for Ålfotbreen, Nigardsbreen, Storbreen and Hellstugubreen provide an equivalent time series. All datasets were smoothed with a 3 year running mean to remove noise and to allow more regionally meaningful relationships to be identified.

A link has been established between the surface temperature of the Norwegian Sea and mass balance of these glaciers. During the winter, at low temperatures, an increase in MSST coincides with an increase in surface mass balance, whilst at warmer temperatures a decrease is seen. A similar effect is seen in the summer where, for only a small range of low temperatures an increase in mass balance is observed but beyond this mass balance decreases. Piece-wise linear regression has been used to identify this threshold temperature.

The glacier mass balance appears to be influenced by the heat flux delivered by the upper waters of the southern Norwegian Sea via the atmosphere to the land. Positive correlations between MSST and mass balance at low temperatures imply increased precipitation with an increase in MSST. This is likely due to more air mass instability over a warmer sea leading to enhanced cyclogenesis. Concomitant with this influence on precipitation there is a more direct impact on the air temperature: heat flux between the ocean and atmosphere can warm or cool the lower atmosphere. A threshold temperature has been identified where the increase in mass balance, driven by enhanced precipitation, is offset by the increase in atmospheric temperature which promotes ablation resulting in a negative mass balance.
Response of Norwegian glaciers to North Atlantic climate variability
Miriam Jackson, Hallgeir Elvehøy, Bjarne Kjøllmoen, Liss Marie Andreassen
Corresponding author: Miriam Jackson — mja@nve.no
Glaciers in Norway have exhibited major changes in the last few decades, in response to changes in climate. Several glaciers have been closely monitored over the last few decades, and mass balance, equilibrium line altitude (ELA) and accumulation area ratio (AAR) calculated for each year. The period of observation includes both a time when many but not all glaciers advanced, during the 1990s, and a time of widespread glacier retreat, as occurred during the most recent decade.
Comparing such parameters as ELA with the North Atlantic Oscillation, the dominant mode of winter climate variability in the North Atlantic region shows a reasonable correlation. This correlation is stronger for the more ‘maritime’ glaciers, that lie nearer the coast and have higher winter and summer mass balances, compared with the more ‘continental’, drier glaciers further inland. For example, Ålfotbreen lies very near the west coast of Norway and commonly gets 10 m of snow in the winter and had a correlation of 0.57, whereas Hardangerjøkulen and Hellstugubreen further inland both had correlations of about 0.40.
A calving law for ice sheet models; Investigating the role of surface and basal melt on dynamics of Greenland outlet glaciers
Faezeh M. Nick, Cornelis van der Veen
Corresponding author: Cornelis van der Veen — cjvdv@ku.edu
Calving of icebergs accounts for perhaps as much as half the ice transferred from the Greenland Ice Sheet into the surrounding ocean, and virtually all of the ice loss from the Antarctic Ice Sheet. We have formulated a calving model that can be readily incorporated into time-evolving numerical ice-flow models. Our model is based on downward penetration of water-filled surface crevasses and upward propagation of basal crevasses. A calving event occurs when the depth of the surface crevasse (which increases as melting progresses through the summer) reaches the height of the basal crevasse.
Our numerical ice sheet model is able to reproduce observed seasonal changes of Greenland outlet glaciers, such as fluctuations in flow speed and terminus positions. In contrast to earlier models in which calving rate is linked to local water depth or height above buoyancy, the new calving relation allows for the formation of a floating ice tongue. We have applied the model to Helheim Glacier on the east coast and Petermann Glacier in north of Greenland. This modeling study provides insights into the role of surface and basal hydrology to ice sheet dynamics and on how to incorporate calving in ice sheet models and therefore advances our ability to predict future ice sheet change.
Investigation of elevation changes of rapidly changing Greenland outlet glaciers
Beata Csatho, Anton Schenk, Cornelis van der Veen, Leigh Stearns
Corresponding author: Beata Csatho — bcsatho@buffalo.edu
Quantitative investigations of the changing dynamics of outlet glaciers have been hampered by the lack of comprehensive data. In recent years, this situation has been remedied. ICESat, combined with airborne laser altimetry, can provide accurate measurements of surface elevation and thickness changes. For selected outlet glaciers additional high-resolution bed topography data are being collected as part of the on-going NASA IceBridge program. Finally, surface velocities derived from various satellite platforms provide crucial information on changing glacier dynamics. Taken together, a rich and diverse data set is emerging that will allow for quantitative studies of select outlet glaciers undergoing rapid changes and for elucidating the processes responsible for initiating and sustaining these changes.

Although airborne and laser altimetry has been providing precise measurements of ice sheet topography since 2003, determining the spatial and temporal distribution of surface changes remains a challenging problem. We have developed a new, comprehensive method, called Surface Elevation Reconstruction And Change detection (SERAC), which determines surface changes by a simultaneous reconstruction of surface topography. The mathematical model is based on the assumption that for a small surface area, only the absolute elevation changes over time but not the shape of the surface patch. Therefore, laser points of all time epochs contribute to the shape parameters; points of each time period determine the absolute elevation of the surface patch at that period. This method provides high-resolution surface topography, precise changes and a rigorous error estimate of the quantities. SERAC also enables the synergistic use of multisensor data.

We combine ICESat and ATM laser altimetry data with elevations from stereo imagery using SERAC for depicting of surface elevation changes over three major outlet glaciers in Greenland (Jakobshavn, Helheim and Kangerlussuaq glaciers). This record, together with a record of surface velocity and the bedrock topography, will be used to investigate the spatial and temporal evolution of thinning and acceleration that follows the weakening and break-up of floating ice tongues or lightly grounded, heavily crevassed ice in the grounding zone. Moreover, long-term records of elevation changes of outlet glaciers since the Little Ice Age, reconstructed from historical photography, will be examined to place ongoing rapid changes into historical perspective. Finally, ice surface changes of nearby land-terminating glaciers and land-based ice margins will be determined, to contrast thinning related to local surface mass balance changes with climatic induced dynamic thinning of the marine-terminating outlet glaciers.
Dynamic controls on Eklutna Glacier Mass Loss
Louis C Sass, Stephen Price, Michael G Loso, Shad O'Neel, Joseph A MacGregor, Ginny Catania, Chris Larsen
Corresponding author: Louis C Sass — lsass@alaskapacific.edu
Here we investigate the role of ice dynamics in observed mass loss at Eklutna Glacier, south-central Alaska. Meltwater from the glacier is a primary input to Eklutna Reservoir, which supplies >80% of the drinking water and >10% of the power to nearby Anchorage, Alaska. Net mass loss from Eklutna Glacier is responsible for approximately 10% of the inflow to Eklutna Reservoir since the 1950’s. Airborne laser profiling shows that much of the related volume loss occurred in a broad basin near the top of the glacier, which is unusual. In this work we examine the relative importance of surface mass balance and ice dynamics in this volume loss. We supplemented an ongoing mass-balance monitoring program on Eklutna with ice-thickness and surface velocity-measurements. Using 5-MHz radar, we measured a maximum ice thickness of 430 m in the upper basin, which is separated from the lower glacier by a prominent bedrock sill. Summer surface velocities, measured with GPS, vary from 7 to 18 cm/day and increase down glacier. Geometric constraints on flux through the overdeepening upstream from the sill must result in unusually high rates of deformation in the upper portion of the ice column. We calculate the relative ratio of depth-averaged to surface velocity across our survey grid from measured surface velocities, surface mass balance, thinning rates, and geometry. This ratio is at a minimum for ice flowing out of the overdeepening toward the sill and at a maximum for ice flowing just below the sill. From the overdeepening to the sill the effective strain rate is dominated by normal strain. Both of these observations are consistent with unusually high strain rates in the upper portion of the ice column, which suggests that surface slopes through the overdeepening are maintained largely by these normal strain rates occurring in the non-basal ice. A decrease in ice flux would then enable a significant change in surface slope, allowing the basin to thin and decrease the accumulation area of the glacier. We hypothesize that a positive feedback between thinning and negative surface mass balance is underway in the upper basin and that this feedback will continue until the glacier terminus retreats past the bedrock sill. These findings have broader significance for understanding the response times of alpine glaciers to climate change.
Development of an ice sheet albedo parameterization for use in climate models
B P Gready, J E Box, M J Sharp, A B G Bush
Corresponding author: B P Gready — gready@ualberta.ca
Surface Mass Balance (SMB) is the net input in the overall mass budget of Arctic ice sheets and ice caps. It also provides a necessary surface boundary condition for ice sheet models that are being developed to predict dynamic ice loss (the other significant term in an ice sheet/cap mass budget). Recently, researchers have used regional climate models such as RACMO2, Polar MM5 and, Polar WRF in physically based modeling of SMB. These studies have enabled spatially distributed, SMB estimates over the entire Greenland Ice Sheet on the order of 10 km grid spacing. While such studies have been revolutionary, there are still important missing pieces of the models and large uncertainties in model output.

In this study, the albedo parameterization within Polar WRF is a major source of model uncertainty. We present recent development of an “inline” albedo parameterization within Polar WRF. Albedo is parameterized as a function of snow depth and time since last snowfall, allowing snow evolution to span multiple model restarts. Model output is calibrated on a 25 km grid over Western Greenland, using the MODIS albedo product for the 2005 summer, and is subsequently run for the summer of 2007, for which model performance is evaluated. Preliminary analysis indicates that the parameterization improves model accuracy.

Ultimately this work provides a practical advancement in the development of a physically based method for estimating SMB that does not require tuning to specific locations or climatology. Such a method could also be used in combination with Global Circulation Model output to predict future SMB trends over ice sheets.
Chronology of Late Quaternary glaciation and Landform evolution in the Pindar valley, Kumaun Himalaya
Rameshwar Bali, K.K. Agarwal, S. Nawaz Ali, S.K. Rastogi, Kalyan Krishna
Corresponding author: Rameshwar Bali — rameshbali@rediffmail.com
The timing and the palaeoglacial extent of various episodes of Late Quaternary period is not very well documented in the central Indian Himalayan region. Systematic field investigations in the upper reaches of Pindar glacial valley has helped in identifying a number of glacially sculptured landforms. During the present work, periglacial geomorphic features have been systematically studied, recorded and mapped to reconstruct the pattern of Late Quaternary glaciation. After carefully examining and dating some of glacial deposits, an attempt has been made to build up moraine stratigraphy along the Pindar valley. Remnants of the recessional moraines near Khati (2925 m asl), about 22 km downstream of the present day snout, suggests that the Pindari trunk glacier during Stage I had probably extended upto Khati (Khati Stage), sometimes during the Middle to Late Quaternary. The LGM in the area seems to have occurred during the early part of last glacial cycle i.e. MIS-3 (23-58 Ka BP). The valley cross section upstream of Khati suggests the presence of a broad U- shaped valley which has subsequently been modified into a narrow one, along the valley floor. During the Stage II (25 ka BP, Phurkia Stage), the glacier again advanced upto about 7 kms downstream of the present snout. The extent of Stage II advance is marked by the well developed and preserved terminal moraine observed along the right valley wall before Phurkia. During its recessional journey that continued upto around 7.0 Ka BP., the glacial snout reached almost upto the altitude of the present day snout. This is clearly evidenced by the presence and dating of a set of recessional moraines in the shadow of rock knob locally named as Kupi Dhura. Thereafter, there was a sudden and sporadic advance of the trunk glacier during Stage III (6.0 – 1.0 ka BP). Due to sudden advance and presence of rock knob, the Stage III advance did not cover the entire width of the valley. The left lateral moraine of the Stage III advance of trunk glacier is found well preserved as a morainic ridge in almost centre of the trunk valley. A number of crescent shaped recessional moraines disposed along the present day valley floor represent the Stage IV glacial advancement, coinciding with the global Little Ice age. By observing the morphotectonic disposition of landforms and carrying out Anisotropy of magnetic susceptibility (AMS) fabric analysis, it is inferred that active tectonics has been responsible for the glacio-geomorphic diversity of the area. There has been a major phase of rejuvenation prior to 25 ka that inhibited the downstream advancement of Pindari trunk glacier as well as another phase post 3 ka that modified the orientation of glacio-lacustrine deposit present within the Left lateral moraines of the third phase.
Climate change and Gangotri Glacier, Garhwal Himalaya, India
Dhruv Sen Singh
Corresponding author: Dhruv Sen Singh — dhruvsensingh@rediffmail.com
Gangotri Glacier located in the Kumaun and Garhwal Himalaya is about 30 km long and 0.5 to 2.5 km wide. It has attracted international attention because of its rapid rate of retreat. Many glaciologist and climatologists are of the opinion that it will disappear in the near future due to global warming. The scientific data of retreat available since 1935 indicate that even if it retreats at the rate of 30-35 m/year which is maximum rate in the last 75 years there is no threat to this glacier at least for about 900 years. However the data of retreat of various organizations indicate that the rate is continuously decreasing which is against the global warming and disappearing of this glacier in the near future.
Further more if global warming is the only reason for the rapid rate of retreat then all the glaciers should retreat at the same rate. But all glaciers are retreating at different rate and some are advancing too. It means the local factors such as supraglacial moraines, supraglacial streams, exposure to sun, shadow zone, and neotectonic activities also control the rate of retreat of the glaciers.
The Gangotri glacier has undergone many major and minor fluctuations in its spatial extent which is evidenced by the presence of lateral and recessional moraines occupying different elevations and positions. The left bank Meru and right bank Raktvarna and Chaturangi tributary glaciers were connected to the main glacier once in the past. The presence of three levels of lateral moraines on the left valley wall indicates wide extent of this glacier in the past.
The rate of retreat is not uniform and varies between 10 m/year to 35 m/year for different years and decades. The area vacated by glacier has also no uniform trend; it shows many ups and downs in its pattern. The present paper deals with the interrelationships of climate change and Gangotri Glacier.
Gangotri Glacier located in the Kumaun and Garhwal Himalaya is about 30 km long and 0.5 to 2.5 km wide. It has attracted international attention because of its rapid rate of retreat. Many glaciologist and climatologists are of the opinion that it will disappear in the near future due to global warming. The scientific data of retreat available since 1935 indicate that even if it retreats at the rate of 30-35 m/year which is maximum rate in the last 75 years there is no threat to this glacier at least for about 900 years. However the data of retreat of various organizations indicate that the rate is continuously decreasing which is against the global warming and disappearing of this glacier in the near future.
Further more if global warming is the only reason for the rapid rate of retreat then all the glaciers should retreat at the same rate. But all glaciers are retreating at different rate and some are advancing too. It means the local factors such as supraglacial moraines, supraglacial streams, exposure to sun, shadow zone, and neotectonic activities also control the rate of retreat of the glaciers.
The Gangotri glacier has undergone many major and minor fluctuations in its spatial extent which is evidenced by the presence of lateral and recessional moraines occupying different elevations and positions. The left bank Meru and right bank Raktvarna and Chaturangi tributary glaciers were connected to the main glacier once in the past. The presence of three levels of lateral moraines on the left valley wall indicates wide extent of this glacier in the past.
The rate of retreat is not uniform and varies between 10 m/year to 35 m/year for different years and decades. The area vacated by glacier has also no uniform trend; it shows many ups and downs in its pattern. The present paper deals with the interrelationships of climate change and Gangotri Glacier.