TCD - Latest Articles

Quantification of ikaite in Antarctic sea ice

Fri, 03 Feb 2012 00:00:00 +0100

Quantification of ikaite in Antarctic sea ice

The Cryosphere Discussions, 6, 505-530, 2012

Author(s): M. Fischer, D. N. Thomas, A. Krell, G. Nehrke, J. Göttlicher, L. Norman, C. Riaux-Gobin, and G. S. Dieckmann

Calcium carbonate precipitation in sea ice can increase pCO₂ during precipitation in winter and decrease pCO₂ during dissolution in spring. CaCO₃ precipitation in sea ice is thought to potentially drive significant CO₂ uptake by the ocean. However, little is known about the quantitative spatial and temporal distribution of CaCO₃ within sea ice. This is the first quantitative study of hydrous calcium carbonate, as ikaite, in sea ice and discusses its potential significance for the carbon cycle in polar oceans. Ice cores and brine samples were collected from pack and land fast sea ice between September and December 2007 during an expedition in the East Antarctic and another off Terre Adélie, Antarctica. Samples were analysed for CaCO₃, Salinity, DOC, DON, Phosphate, and total alkalinity. A relationship between the measured parameters and CaCO₃ precipitation could not be observed. We found calcium carbonate, as ikaite, mostly in the top layer of sea ice with values up to 126 mg ikaite per liter melted sea ice. This potentially represents a contribution between 0.12 and 9 Tg C to the annual carbon flux in polar oceans. The horizontal distribution of ikaite in sea ice was heterogenous. We also found the precipitate in the snow on top of the sea ice.

Evaluation of the criticality of cracks in ice shelves using finite element simulations

Wed, 01 Feb 2012 00:00:00 +0100

Evaluation of the criticality of cracks in ice shelves using finite element simulations

The Cryosphere Discussions, 6, 469-503, 2012

Author(s): C. Plate, R. Müller, A. Humbert, and D. Gross

The ongoing disintegration of large ice shelf parts in Antarctica raise the need for a better understanding of the physical processes that trigger critical crack growth in ice shelves. Finite elements in combination with configurational forces facilitate the analysis of single surface fractures in ice under various boundary conditions and material parameters. The principles of linear elastic fracture mechanics are applied to show the strong influence of different depth dependent functions for the density and the Young's modulus on the stress intensity factor K_I at the crack tip. Ice, for this purpose, is treated as a compressible solid and the consequences of this choice in comparison to the predominant incompressible approaches is discussed. The computed stress intensity factors K_I for dry and water filled cracks are compared with critical values K_Ic from measurements that can be found in literature.

Sensitivity of basal conditions in an inverse model: Vestfonna Ice-Cap, Nordaustlandet/Svalbard

Tue, 31 Jan 2012 00:00:00 +0100

Sensitivity of basal conditions in an inverse model: Vestfonna Ice-Cap, Nordaustlandet/Svalbard

The Cryosphere Discussions, 6, 427-467, 2012

Author(s): M. Schäfer, T. Zwinger, P. Christoffersen, F. Gillet-Chaulet, K. Laakso, R. Pettersson, V. A. Pohjola, T. Strozzi, and J. C. Moore

The dynamics of Vestfonna ice-cap (Svalbard) is dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast flowing outlet glaciers. Hence it is a challenging target for ice-flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice-cap. Here we use the Full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice-cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier – a simple parameterization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small not to adversely affect the fidelity of the model.

Glacier changes and climate trends derived from multiple sources in the data scarce Cordillera Vilcanota region, Southern Peruvian Andes

Mon, 30 Jan 2012 00:00:00 +0100

Glacier changes and climate trends derived from multiple sources in the data scarce Cordillera Vilcanota region, Southern Peruvian Andes

The Cryosphere Discussions, 6, 387-426, 2012

Author(s): N. Salzmann, C. Huggel, M. Rohrer, W. Silverio, B. G. Mark, P. Burns, and C. Portocarrero

The role of glaciers as temporal water reservoirs is particularly pronounced in the (outer) tropics because of the very distinct wet-dry seasons. Rapid glacier retreat caused by climatic changes is thus a major concern and decision makers demand urgently for regional/local glacier evolution trends, ice mass estimates and runoff assessments. However, in remote mountain areas, spatial and temporal data coverage is typically very scarce and this is further complicated by a high spatial and temporal variability in regions with complex topography. Here, we present an approach on how to deal with these constraints. For the Cordillera Vilcanota (Southern Peruvian Andes), which is the second largest glacierised Cordillera in Peru (after the Cordillera Blanca) and also comprises the Quelccaya Ice Cap, we assimilate a comprehensive multi-decadal collection of available glacier and climate data from multiple sources (satellite images, meteorological station data and climate Reanalysis), and analyze them for respective changes in glacier area and volume and related trends in air temperature, precipitation and specific humidity. In general, the climate data show a moderate (compared to other alpine regions) increase in air temperature, weak and not significant trends for precipitation sums, and an increase in specific humidity at the 500 hPa level. The latter is consistent with observed increase in water vapour at the tropopause level during the past decades. It is likely that the increase in specific humidity played a major role in the observed massive ice loss of the Cordillera Vilcanota over the past decades.

Modelling borehole temperatures in Southern Norway – insights into permafrost dynamics during the 20th and 21st century

Fri, 27 Jan 2012 00:00:00 +0100

Modelling borehole temperatures in Southern Norway – insights into permafrost dynamics during the 20th and 21st century

The Cryosphere Discussions, 6, 341-385, 2012

Author(s): T. Hipp, B. Etzelmüller, H. Farbrot, T. V. Schuler, and S. Westermann

A transient heat flow model was used to simulate both past and future ground temperatures of mountain permafrost and associated active layer thickness in Southern Norway. The model was forced by reconstructed air temperature starting from 1860, approximately coinciding with the Little Ice Age in the region. The impact of climate warming on mountain permafrost until 2100 is assessed by using downscaled air temperatures from a multi-model ensemble for the A1B scenario. For 13 borehole locations, records over three consecutive years of ground temperatures, air temperatures and snow cover data are available for model calibration and validation. The boreholes are located at different elevations and in substrates with different thermal properties. With an increase of air temperature of ~+1.5 °C over 1860–2010 and an additional warming of +2.8 °C until 2100, we simulate the evolution of ground temperatures for the borehole locations. According to model results, the active-layer thickness has increased since 1860 by 0.5–5 m and >10 m for the sites Juvvasshøe and Tron, respectively. The simulations also suggest that at an elevation of about 1900 m a.s.l. permafrost will degrade until the end of this century with a probability of 55–75% given the chosen A1B scenario.

Improved modelling of Siberian river flow through the use of an alternative frozen soil hydrology scheme in a land surface model

Tue, 24 Jan 2012 00:00:00 +0100

Improved modelling of Siberian river flow through the use of an alternative frozen soil hydrology scheme in a land surface model

The Cryosphere Discussions, 6, 309-340, 2012

Author(s): D. L. Finney, E. Blyth, and R. Ellis

A parameterisation to incorporate the effects of frozen soil on modelled hydrology is described and implemented within a land surface model, the Joint UK Land Surface Environment Simulator. It is shown to generally improve the modelled flow of Siberian rivers compared to observations, specifically in seasons of freezing or thawing soil. Most noticeably, the revised model increases the snowmelt flow peak by 26–100% compared to the control model thereby better matching observed flows. The model physics resulting in the changes to river flow are discussed and attention is given to the effect of inaccuracies in snowfall driving data which can hinder the comparison of new model processes.

Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

Tue, 24 Jan 2012 00:00:00 +0100

Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

The Cryosphere Discussions, 6, 267-308, 2012

Author(s): F. Pattyn, C. Schoof, L. Perichon, R. C. A. Hindmarsh, E. Bueler, B. de Fleurian, G. Durand, O. Gagliardini, R. Gladstone, D. Goldberg, G. H. Gudmundsson, V. Lee, F. M. Nick, A. J. Payne, D. Pollard, O. Rybak, F. Saito, and A. Vieli

Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady-state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including in fixed-grid models that generally perform poorly at coarse resolution. Fixed grid models with nested grid representations of the grounding line are able to generate accurate steady-state positions, but can be inaccurate over transients. Only one full Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full Stokes models remains to be determined in detail, especially during transients.

Simulating melt, runoff and refreezing on Nordenskiöldbreen, Svalbard, using a coupled snow and energy balance model

Fri, 20 Jan 2012 00:00:00 +0100

Simulating melt, runoff and refreezing on Nordenskiöldbreen, Svalbard, using a coupled snow and energy balance model

The Cryosphere Discussions, 6, 211-266, 2012

Author(s): W. J. J. van Pelt, J. Oerlemans, C. H. Reijmer, V. A. Pohjola, R. Pettersson, and J. H. van Angelen

A distributed energy balance model is coupled to a multi-layer snow model in order to study the mass balance evolution and the impact of refreezing on the mass budget of Nordenskiöldbreen, Svalbard. The model is forced with output of a regional climate model (RACMO) and meteorological data from Svalbard Airport. Extensive calibration and initialisation are performed to increase the model accuracy. For the period 1989–2010, we find a mean net mass balance of −0.39 m w.e. a⁻¹. Refreezing contributes on average 0.27 m w.e. a⁻¹ to the mass budget and is most pronounced in the accumulation zone. The simulated mass balance, radiative fluxes and subsurface profiles are validated against observations and are generally in good agreement. Climate sensitivity experiments reveal a non-linear, seasonally dependent response of the mass balance, refreezing and runoff to changes in temperature and precipitation. Output of the climate sensitivity experiments is used in combination with temperature and precipitation time-series to extend mass balance time-series in the past and the future to obtain estimates for the period 1912–2085. It is shown that including seasonality in climate change, with less pronounced summer warming, has a major impact on future mass balance and ELA estimates. Due to compensating effects, the contribution of refreezing hardly changes in a future climate.

Statistical adaptation of ALADIN RCM outputs over the French alpine massifs – application to future climate and snow cover

Thu, 19 Jan 2012 00:00:00 +0100

Statistical adaptation of ALADIN RCM outputs over the French alpine massifs – application to future climate and snow cover

The Cryosphere Discussions, 6, 171-210, 2012

Author(s): M. Rousselot, Y. Durand, G. Giraud, L. Mérindol, I. Dombrowski-Etchevers, and M. Déqué

In this study, snowpack scenarios are modelled across the French Alps using dynamically downscaled variables from the ALADIN Regional Climate Model (RCM) for the control period (1961–1990) and three emission scenarios (SRES B1, A1B and A2) by the mid- and late of the 21st century (2021–2050 and 2071–2100). These variables are statistically adapted to the different elevations, aspects and slopes of the alpine massifs. For this purpose, we use a simple analogue criterion with ERA40 series as well as an existing detailed climatology of the French Alps (Durand et al., 2009a) that provides complete meteorological fields from the SAFRAN analysis model. The resulting scenarios of precipitation, temperature, wind, cloudiness, longwave and shortwave radiation, and humidity are used to run the physical snow model CROCUS and simulate snowpack evolution over the massifs studied. The seasonal and regional characteristics of the simulated climate and snow cover changes are explored, as is the influence of the scenarios on these changes. Preliminary results suggest that the Snow Water Equivalent (SWE) of the snowpack will decrease dramatically in the next century, especially in the Southern and Extreme Southern part of the Alps. This decrease seems to result primarily from a general warming throughout the year, and possibly a deficit of precipitation in the autumn. The magnitude of the snow cover decline follows a marked altitudinal gradient, with the highest altitudes being less exposed to climate change. Scenario A2, with its high concentrations of greenhouse gases, results in a SWE reduction roughly twice as large as in the low-emission scenario B1 by the end of the century. This study needs to be completed using simulations from other RCMs, since a multi-model approach is essential for uncertainty analysis.

Brief Communication "Importance of slope-induced error correction in elevation change estimates from radar altimetry"

Tue, 17 Jan 2012 00:00:00 +0100

Brief Communication "Importance of slope-induced error correction in elevation change estimates from radar altimetry"

The Cryosphere Discussions, 6, 159-170, 2012

Author(s): R. T. W. L. Hurkmans, J. L. Bamber, and J. A. Griggs

In deriving elevation change rates (dH/dt) from radar altimetry, the slope-induced error is usually assumed to cancel out in repeat measurements. These measurements, however, represent a location that can be significantly further upslope than assumed, causing an underestimate of the basin-integrated volume change. In a case-study for the fast-flowing part of Jakobshavn Isbræ, we show that a relatively straightforward correction for slope-induced error increases elevation change rates by several metres and increases the volume change by 32% for the region of interest.

Initial sea-ice growth in open water: properties of grease ice and nilas

Fri, 13 Jan 2012 00:00:00 +0100

Initial sea-ice growth in open water: properties of grease ice and nilas

The Cryosphere Discussions, 6, 125-158, 2012

Author(s): A. K. Naumann, D. Notz, L. Håvik, and A. Sirevaag

To investigate initial sea-ice growth in open water, we carried out an ice-tank study with three different setups: grease ice grew in experiments with waves and in experiments with a current and wind, while nilas formed in a quiescent experimental setup. In this paper we focus on the differences in bulk salinity, solid fraction and thickness between these two ice types.

We find that the bulk salinity of the grease-ice layer remains almost constant until the ice starts to consolidate. In contrast, the bulk salinity of nilas is in the first hours of ice formation well described by a linear decrease of 2.1 g kg⁻¹ h⁻¹ independent of air temperature. Such rapid decrease in bulk salinity can be understood qualitatively in the light of a Rayleigh number, the maximum of which is reached while the nilas is still less than 1 cm thick.

Comparing three different methods to measure solid fraction in grease ice based on (a) salt conservation, (b) mass conservation and (c) energy conservation, we find that the method based on salt conservation does not give reliable results if the salinity of the interstitial water is approximated as being equal to the salinity of the upper water layer. Instead the increase in salinity of the interstitial water during grease-ice formation must be taken into account. We find that the solid fraction of grease ice is relatively constant with values of 0.25, whereas it increases to values as high as 0.5 as soon as the grease ice consolidates at its surface. In contrast, the solid fraction of nilas increases continuously in the first hours of ice formation.

The ice thickness is found to be twice as large in the first 24 h of ice formation in the setup with a current and wind compared to the other two setups, since the wind keeps parts of the water surface ice free. The development of the ice thickness can be reproduced well with simple, one dimensional models given only the air temperature or the ice surface temperature.

Numerical modeling of permafrost dynamics in Alaska using a high spatial resolution dataset

Fri, 06 Jan 2012 00:00:00 +0100

Numerical modeling of permafrost dynamics in Alaska using a high spatial resolution dataset

The Cryosphere Discussions, 6, 89-124, 2012

Author(s): E. E. Jafarov, S. S. Marchenko, and V. E. Romanovsky

Climate projections for the 21st century indicate that there could be a pronounced warming and permafrost degradation in the Arctic and sub-Arctic regions. Climate warming is likely to cause permafrost thawing with subsequent effects on surface albedo, hydrology, soil organic matter storage and greenhouse gas emissions. To assess possible changes in the permafrost thermal state and active layer thickness, we implemented the GIPL2-MPI transient numerical model for the entire Alaska permafrost domain. Input parameters to the model are spatial datasets of mean monthly air temperature and precipitation, prescribed thermal properties of the multilayered soil column, and water content which are specific for each soil class and geographical location. As a climate forcing we used the composite of five IPCC Global Circulation Models that has been downscaled to 2 by 2 km spatial resolution by Scenarios Network for Alaska Planning (SNAP) group.

In this paper we present the preliminary modeling results based on input of five-model composite with A1B carbon emission scenario. The model has been calibrated according to the annual borehole temperature measurements for the State of Alaska. We also performed more detailed calibration for fifteen shallow borehole stations where high quality data are available on daily basis. To validate the model performance we compared simulated active layer thicknesses with observed data from CALM active layer monitoring stations. Calibrated model was used to address possible ground temperature changes for the 21st century. The model simulation results show the widespread permafrost degradation in Alaska could begin in 2040–2099 time frame within the vast area southward from the Brooks Range except for the high altitudes of the Alaska Range and Wrangell Mountains.

Remote sensing of sea ice: advances during the DAMOCLES project

Tue, 03 Jan 2012 00:00:00 +0100

Remote sensing of sea ice: advances during the DAMOCLES project

The Cryosphere Discussions, 6, 37-88, 2012

Author(s): G. Heygster, V. Alexandrov, G. Dybkjær, F. Girard-Ardhuin, W. von Hoyningen-Huene, I. L. Katsev, A. Kokhanovsky, T. Lavergne, A. V. Malinka, C. Melsheimer, L. Toudal Pedersen, A. S. Prikhach, R. Saldo, R. Tonboe, H. Wiebe, and E. P. Zege

In the Arctic, global warming is particularly pronounced so that we need to monitor its development continuously. On the other hand, the vast and hostile conditions make in situ observation difficult, so that available satellite observations should be exploited in the best possible way to extract geophysical information. Here, we give a résumé of the sea ice remote sensing efforts of the EU project DAMOCLES (Developing Arctic Modeling and Observing Capabilities for Long-term Environmental Studies). The monthly variation of the microwave emissivity of first-year and multiyear sea ice has been derived for the frequencies of the microwave imagers like AMSR-E and sounding frequencies of AMSU, and has been used to develop an optimal estimation method to retrieve sea ice and atmospheric parameters simultaneously. A sea ice microwave emissivity model has been used together with a thermodynamic model to establish relations between the emisivities at 6 GHz and 50 GHz. At the latter frequency, the emissivity is needed for assimilation into atmospheric circulation models, but more difficult to observe directly. A method to determine the effective size of the snow grains from observations in the visible range (MODIS) is developed and applied. The bidirectional reflectivity distribution function (BRDF) of snow, which is an essential input parameter to the retrieval, has been measured in situ on Svalbard during the DAMOCLES campaign, and a BRDF model assuming aspherical particles is developed. Sea ice drift and deformation is derived from satellite observations with the scatterometer ASCAT (62.5 km grid spacing), with visible AVHRR observations (20 km), with the synthetic aperture radar sensor ASAR (10 km), and a multi-sensor product (62.5 km) with improved angular resolution (Continuous Maximum Cross Correlation, CMCC method) is presented. CMCC is also used to derive the sea ice deformation, important for formation of sea ice leads (diverging deformation) and pressure ridges (converging). The indirect determination of sea ice thickness from altimeter freeboard data requires knowledge of the ice density and snow load on sea ice. The relation between freeboard and ice thickness is investigated based on the airborne Sever expeditions conducted between 1928 and 1993.

Spatial patterns of North Atlantic Oscillation influence on mass balance variability of European Glaciers

Tue, 03 Jan 2012 00:00:00 +0100

Spatial patterns of North Atlantic Oscillation influence on mass balance variability of European Glaciers

The Cryosphere Discussions, 6, 1-35, 2012

Author(s): B. Marzeion and A. Nesje

We present and validate a set of minimal models of glacier mass balance variability. The most skillful model is then applied to reconstruct 7735 individual time series of mass balance variability for all glaciers in the European Alps and Scandinavia. Subsequently, we investigate the influence of atmospheric variability associated with the North Atlantic Oscillation (NAO) on the glaciers' mass balances.

We find a spatial coherence in the glaciers' sensitivity to NAO forcing which is caused by regionally similar mechanisms relating the NAO forcing to the mass balance: In Southwestern Scandinavia, winter precipitation causes a correlation of mass balances with the NAO. In Northern Scandinavia, temperature anomalies outside the core winter season cause an anti-correlation between NAO and mass balances. In the Western Alps, both temperature and winter precipitation anomalies lead to a weak anti-correlation of mass balances with the NAO, while in the Eastern Alps, the influences of winter precipitation and temperature anomalies tend to cancel each other, and only on the southern side a slight anti-correlation of mass balances with the NAO prevails.

Stable isotope and gas properties of two ice wedges from Cape Mamontov Klyk, Laptev Sea, Northern Siberia

Wed, 21 Dec 2011 00:00:00 +0100

Stable isotope and gas properties of two ice wedges from Cape Mamontov Klyk, Laptev Sea, Northern Siberia

The Cryosphere Discussions, 5, 3627-3660, 2011

Author(s): T. Boereboom, D. Samyn, H. Meyer, and J.-L. Tison

This paper presents and discusses the texture, fabric and gas properties (contents of total gas, O₂, N₂, CO₂, and CH₄) of two ice wedges from Cape Mamontov Klyk, Laptev Sea, Northern Siberia. The two ice wedges display contrasting structures: one being of relatively "clean" ice and the other showing clean ice at its centre as well as debris-rich ice on its sides (referred to as ice-sand wedge). A comparison of gas properties, crystal size, fabrics and stable isotope data (δ¹⁸O and δD) allows discriminating between three different facies of ice with specific paleoenvironmental signatures, suggesting different climatic conditions and rates of biological activity. More specifically, total gas content and composition reveal variable intensities of meltwater infiltration and show the impact of biological processes with contrasting contributions from anaerobic and aerobic conditions. Stable isotope data are shown to be valid for discussing changes in paleoenvironmental conditions and/or decipher different sources for the snow feeding into the ice wedges with time. Our data also give support to the previous assumption that the composite ice wedge was formed in Pleistocene and the ice wedge in Holocene times. This study sheds more light on the conditions of ice wedge growth under changing environmental conditions.

Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps

Wed, 21 Dec 2011 00:00:00 +0100

Glacier ice in rock glaciers: a case study in the Vanoise Massif, Northern French Alps

The Cryosphere Discussions, 5, 3597-3626, 2011

Author(s): S. Monnier, C. Camerlynck, F. Rejiba, C. Kinnard, and P.-Y. Galibert

We investigated the Sachette rock glacier, Vanoise Massif, Northern French Alps, using former equilibrium line altitude reconstruction from glacial deposits, aerial photograph analysis, and ground-penetrating radar (GPR). The rock glacier is a young (probably <6000 yr) and active landform. The GPR survey consisted of two CMP measurements and four constant-offset profiles. From CMP measurements, the radar wave velocity in exposed shallow massive ice is 0.165–0.17 m ns⁻¹. The constant-offset GPR data was processed and analysed in order to reconstruct the stratigraphy and model the radar wave velocity in two dimensions. The integration of the morphology, the velocity models, and the stratigraphy emphasized, in the upper half of the rock glacier, the good correspondence between high radar wave velocities (>0.15–0.16 m ns⁻¹) and reflectors having a dipping-syncline structure, typical of true glaciers. Consequently, the rock glacier structure is described as being constituted of a glacial massive ice core embedded into diamictons. Our study of the Sachette rock glacier highlights possible significance of rock glaciers and interactions between glacier and permafrost in alpine environments.

A new glacier inventory for 2009 reveals spatial and temporal variability in glacier response to atmospheric warming in the Northern Antarctic Peninsula, 1988–2009

Wed, 21 Dec 2011 00:00:00 +0100

A new glacier inventory for 2009 reveals spatial and temporal variability in glacier response to atmospheric warming in the Northern Antarctic Peninsula, 1988–2009

The Cryosphere Discussions, 5, 3541-3595, 2011

Author(s): B. J. Davies, J. L. Carrivick, N. F. Glasser, M. J. Hambrey, and J. L. Smellie

The Northern Antarctic Peninsula has recently exhibited ice-shelf disintegration, glacier recession and acceleration. However, the dynamic response of land-terminating, ice-shelf tributary and tidewater glaciers has not yet been quantified or assessed for variability, and there are sparse published data for glacier classification, morphology, area, length or altitude. This paper firstly uses ASTER images from 2009 and a SPIRIT DEM from 2006 to classify the area, length, altitude, slope, aspect, geomorphology, type and hypsometry of 194 glaciers on Trinity Peninsula, Vega Island and James Ross Island. Secondly, this paper uses LANDSAT-4 and ASTER images from 1988 and 2001 and data from the Antarctic Digital Database (ADD) from 1997 to document glacier change 1988–2009. From 1988–2001, 90 % of glaciers receded, and from 2001–2009, 79 % receded. Glaciers on the western side of Trinity Peninsula retreated relatively little. On the eastern side of Trinity Peninsula, the rate of recession of ice-shelf tributary glaciers has slowed from 12.9 km² a⁻¹ (1988–2001) to 2.4 km² a⁻¹ (2001–2009). Tidewater glaciers on the drier, cooler Eastern Trinity Peninsula experienced fastest recession from 1988–2001, with limited frontal retreat after 2001. Land-terminating glaciers on James Ross Island also retreated fastest in the period 1988–2001. Large tidewater glaciers on James Ross Island are now declining in areal extent at rates of up to 0.04 km² a⁻¹. This east-west difference is largely a result of orographic temperature and precipitation gradients across the Antarctic Peninsula. Strong variability in tidewater glacier recession rates may result from the influence of glacier length, altitude, slope and hypsometry on glacier mass balance. High snowfall means that the glaciers on the Western Peninsula are not currently rapidly receding. Recession rates on the eastern side of Trinity Peninsula are slowing as the floating ice tongues retreat into the fjords and the glaciers reach a new dynamic equilibrium. The rapid glacier recession of tidewater glaciers on James Ross Island is likely to continue because of their low elevations and flat profiles. In contrast, the higher and steeper tidewater glaciers on the Eastern Antarctic Peninsula will attain more stable frontal positions after low-lying ablation areas are removed.

Melting of Northern Greenland during the last interglacial

Wed, 21 Dec 2011 00:00:00 +0100

Melting of Northern Greenland during the last interglacial

The Cryosphere Discussions, 5, 3517-3539, 2011

Author(s): A. Born and K. H. Nisancioglu

The Greenland ice sheet (GrIS) is losing mass at an increasing rate, making it the primary contributor to global eustatic sea level rise. Large melting areas and rapid thinning at its margins has raised concerns about its stability. However, it is conceivable that these observations represent the transient adjustment of the fastest reacting parts of the ice sheet, masking slower processes that dominate the long term fate of the GrIS and its contribution to sea level rise.

Studies of the geological past provide valuable information on the long term response of the GrIS to warm periods. We simulate the GrIS during the Eemian interglacial, a period 126 000 yr before present (126 ka) with Arctic temperatures comparable to projections for the end of this century. The northeastern part of the GrIS is unstable and retreats significantly, despite moderate melt rates. Unlike the south and west, strong melting in the northeast is not compensated by high accumulation, or fast ice flow. The analogy with the present warming suggests that in coming decades, positive feedbacks could increase the rate of mass loss of the northeastern GrIS, exceeding the currently observed melting in the south.

Glacier changes from 1966–2009 in the Gongga Mountains, on the south-eastern margin of the Qinghai-Tibetan Plateau and their climatic forcing

Tue, 20 Dec 2011 00:00:00 +0100

Glacier changes from 1966–2009 in the Gongga Mountains, on the south-eastern margin of the Qinghai-Tibetan Plateau and their climatic forcing

The Cryosphere Discussions, 5, 3479-3516, 2011

Author(s): B. Pan, G. Zhang, J. Wang, B. Cao, J. Wang, C. Zhang, H. Geng, and Y. Ji

In order to monitor the changes of the glaciers in the Gongga Mountain region on the south-eastern margin of the Qinghai-Tibetan Plateau, 74 monsoonal temperate glaciers were investigated by comparing the Chinese Glacier Inventory (CGI), recorded in the 1960s, with Landsat MSS in 1974, Landsat TM in 1989, 1994, 2005, and ASTER data in 2009. The remote sensing data have been applied to map the glacier outline by threshold ratio images (TM4/TM5). Moreover, the glacier outlines were verified by GPS survey on four large glaciers (Hailuogou, Mozigou, Yanzigou, and Dagongba) in 2009. The results show that the area dominated by the 74 glaciers has shrunk by 11.3 % (29.2 km²) from 1966 to 2009. Glacier area on the eastern and western slope of the Gongga Mountains decreased by 14.1 km² (5.5 % in 1966) and 15.1 km² (5.9 % in 1966), respectively. The loss in glacier area and length is respectively 0.8 km² and 1146.4 m (26.7 m yr⁻¹) for the Hailuogou glacier, 2.1 km² and 501.8 m (11.7 m yr⁻¹) for the Mozigou Glacier, 0.8 km² and 724.8 m (16.9 m yr⁻¹) for the Yanzigou Glacier, and 2.4 km² and 1002.3 m (23.3 m yr⁻¹) for the Dagongba Glacier. Decades of climate records obtained from three meteorological stations in the Gongga Mountains were analyzed to evaluate the impact of the temperature and precipitation on glacier retreat. During 1966–2009, the mean annual temperature over the eastern and western slope of the Gongga Mountains has been increasing by 0.21 °C/10 yr and 0.13 °C/10 yr, respectively. Moreover, it was stable in the mean annual precipitation. This evidence indicates that the warming of the climate is probably responsible for the glacier retreat in the study region.

Present-day mass changes for the Greenland ice sheet and their interaction with bedrock adjustment

Sun, 11 Dec 2011 00:00:00 +0100

Present-day mass changes for the Greenland ice sheet and their interaction with bedrock adjustment

The Cryosphere Discussions, 5, 3455-3477, 2011

Author(s): M. Olaizola, R. S. W. van de Wal, M. M. Helsen, and B. de Boer

Since the launch in 2002 of the Gravity Recovery and Climate Experiment (GRACE) satellites, several estimates of the mass balance of the Greenland Ice Sheet (GrIS) have been produced. To obtain ice mass changes estimates, data need to be corrected for the effect of deformation changes of the Earth's crust. This is usually done by independently modeling the Glaciological Isostatic Adjustment (GIA) trend and then by removing it from the data. Recently, Wu et al. (2010) proposed a new method to simultaneously estimate GIA and the present-day ice mass change, reporting an ice mass loss of around half of the previously published estimates and a general bedrock subsidence concentrated in the central parts of Greenland. This subsidence appears to be counterintuitive since the ice sheet is loosing mass at present. It was suggested by the authors that this could be a new evidence for additional net past ice accumulation.

In this study, a 3-D ice-sheet model with a surface mass balance forcing based on a mass balance gradient approach has been used to: (a) analyze the bedrock response to changes in the ice load in order to evaluate whether bedrock subsidence and ice thinning can exist simultaneously; (b) study the magnitude and the pattern of the bedrock movement; and (c) evaluate if present-day bedrock subsidence could be the result of a net past mass accumulation.

Under a sine forcing of the annual temperature, that mimics the temperature variations in the Holocene, mass changes yield a delay of the bedrock response of 200 years. Thinning of the ice as well as bedrock subsidence coexist during this period with an order of magnitude equal to the observations by Wu et al. (2010). Although, the resulting pattern of bedrock changes differs considerable: instead of the general bedrock subsidence reported before, we found areas of bedrock uplift as well as areas of bedrock subsidence. A simulation since the last glacial maximum (with the temperature represented as a linear increase from −10 K to present-day) yields a time lag of 1990 years for the bedrock response relative to the temperature forcing and an average uplift of 0.3 mm yr⁻¹ for present-day. The spatial pattern of bedrock-change shows subsidence in the south and northwest as well as uplift in the center and northeast. We obtained these results assuming that the solid earth is a flat elastic lithosphere resting over a viscous relaxed asthenosphere (ELRA model). Using a more sophisticated Self Gravitational Viscoelastic (SGVE) model, we obtain qualitatively similar results: a 2200 years lag and an average uplift for present-day of 0.2 mm yr⁻¹. The spatial pattern of bedrock movement is similar as well. Finally, results are shown for a temperature reconstruction based on ice core data confirming the deglaciation experiment.

According to this study, a bedrock subsidence with a maximum in the central parts of Greenland cannot be that recent explained by a net past ice accumulation. This undermines results suggesting that recent loss is only half of the regular ice mass loss changes.