ALBERT

Beschreibung: Air temperature variability over three glaciers in the Ortles-Cevedale (Italian Alps): effects of glacier disintegration, intercomparison of calculation methods, and impacts on mass balance modeling The Cryosphere Discussions, 8, 6147-6192, 2014 Author(s): L. Carturan, F. Cazorzi, F. De Blasi, and G. Dalla Fontana Glacier mass balance models rely on accurate spatial calculation of input data, in particular air temperature. Lower temperatures (the so-called glacier cooling effect), and lower temperature variability (the so-called glacier damping effect) generally occur over glaciers, compared to ambient conditions. These effects, which depend on the geometric characteristics of glaciers and display a high spatial and temporal variability, have been mostly investigated on medium- to large-size glaciers so far, while observations on smaller ice bodies are scarce. Using a dataset from 8 on-glacier and 4 off-glacier weather stations, collected in summer 2010 and 2011, we analyzed the air temperature variability and wind regime over three different glaciers in the Ortles-Cevedale. The magnitude of the cooling effect and the occurrence of katabatic boundary layer (KBL) processes showed remarkable differences among the three ice bodies, suggesting the likely existence of important reinforcing mechanisms during glacier decay and disintegration. None of the methods proposed in the literature for calculating on-glacier temperature from off-glacier data fully reproduced our observations. Among them, the more physically-based procedure of Greuell and Böhm (1998) provided the best overall results where the KBL prevail, but it was not effective elsewhere (i.e. on smaller ice bodies and close to the glacier margins). The accuracy of air temperature estimations strongly impacted the results from a mass balance model which was applied to the three investigated glaciers. Most importantly, even small temperature deviations caused distortions in parameter calibration, thus compromising the model generalizability.

Beschreibung: Strategy of valid 14 C dates choice in syngenetic permafrost The Cryosphere Discussions, 8, 5589-5621, 2014 Author(s): Y. K. Vasil'chuk and A. C. Vasil'chuk The main problem of radiocarbon dating within permafrost is the uncertain reliability of the 14 C dates. Syngenetic sediments contain allochthonous organic deposit that originated at a distance from its present position. Due to the very good preservation of organic materials in permafrost conditions and numerous re-burials of the fossils from ancient deposits into younger ones the dates could be both younger and older than the true age of dated material. The strategy for the most authentic radiocarbon date selection for dating of syncryogenic sediments is considered taking into account the fluvial origin of the syngenetic sediments. The re-deposition of organic material is discussed in terms of cyclic syncryogenic sedimentation and also the possible re-deposition of organic material in subaerial-subaqueous conditions. The advantages and the complications of dating organic micro-inclusions from ice wedges by the accelerator mass spectrometry (AMS) method are discussed applying to true age of dated material search. Radiocarbon dates of different organic materials from the same samples are compared. The younger age of the yedoma from cross-sections of Duvanny Yar in Kolyma River and Mamontova Khayata in the mouth of Lena River is substantiated due to the principle of the choice of the youngest 14 C date from the set.

Beschreibung: Simulating the Antarctic ice sheet in the Late-Pliocene warm period: PLISMIP-ANT, an ice-sheet model intercomparison project The Cryosphere Discussions, 8, 5539-5588, 2014 Author(s): B. de Boer, A. M. Dolan, J. Bernales, E. Gasson, H. Goelzer, N. R. Golledge, J. Sutter, P. Huybrechts, G. Lohmann, I. Rogozhina, A. Abe-Ouchi, F. Saito, and R. S. W. van de Wal In the context of future climate change, understanding the nature and behaviour of ice sheets during warm intervals in Earth history is of fundamental importance. The Late-Pliocene warm period (also known as the PRISM interval: 3.264 to 3.025 million years before present) can serve as a potential analogue for projected future climates. Although Pliocene ice locations and extents are still poorly constrained, a significant contribution to sea-level rise should be expected from both the Greenland ice sheet and the West and East Antarctic ice sheets based on palaeo sea-level reconstructions. Here, we present results from simulations of the Antarctic ice sheet by means of an international Pliocene Ice Sheet Modeling Intercomparison Project (PLISMIP-ANT). For the experiments, ice-sheet models including the shallow ice and shelf approximations have been used to simulate the complete Antarctic domain (including grounded and floating ice). We compare the performance of six existing numerical ice-sheet models in simulating modern control and Pliocene ice sheets by a suite of four sensitivity experiments. Ice-sheet model forcing fields are taken from the HadCM3 atmosphere–ocean climate model runs for the pre-industrial and the Pliocene. We include an overview of the different ice-sheet models used and how specific model configurations influence the resulting Pliocene Antarctic ice sheet. The six ice-sheet models simulate a comparable present-day ice sheet, although the models are setup with their own parameter settings. For the Pliocene simulations using the Bedmap1 bedrock topography, some models show a small retreat of the East Antarctic ice sheet, which is thought to have happened during the Pliocene for the Wilkes and Aurora basins. This can be ascribed to either the surface mass balance, as the HadCM3 Pliocene climate shows a significant increase over the Wilkes and Aurora basin, or the initial bedrock topography. For the latter, our simulations with the recently published Bedmap2 bedrock topography indicate a significantly larger contribution to Pliocene sea-level rise from the East Antarctic ice sheet for all six models relative to the simulations with Bedmap1.

Beschreibung: Snow mass decrease in the Northern Hemisphere (1979/80–2010/11) The Cryosphere Discussions, 8, 5623-5644, 2014 Author(s): Z. Li, J. Liu, L. Huang, N. Wang, B. Tian, J. Zhou, Q. Chen, and P. Zhang Snow cover has a key effect on climate change and hydrological cycling, as well as water supply to a sixth of the world's population across the Northern Hemisphere. However, reliable data on trends in snow cover in the Northern Hemisphere is lacking. Snow water equivalent (SWE) is a common measure of the amount of equivalent water of the snow pack. Here we verify the accuracy of three existing global SWE products and merge the most accurate aspects of them to generate a new SWE product covering the last 32 years (1979/80–2010/11). Using this new SWE product, we show that there has been a significant decreasing trend in the total mass of snow in the Northern Hemisphere. The most notable changes in total snow mass are −16.45 ± 6.68 and −13.55 ± 7.80 Gt year −1 in January and February, respectively. These are followed by March and December, which have trends of −12.58 ± 6.88 and −10.70 ± 5.62 Gt year −1 , respectively, from 1979/80 to 2010/11. During the same period, the temperature in the study area raised 0.17 °C decade −1 , which is thought to be the main reason of SWE decline.

Beschreibung: Factors controlling Slope Environmental Lapse Rate (SELR) of temperature in the monsoon and cold-arid glacio-hydrological regimes of the Himalaya The Cryosphere Discussions, 8, 5645-5686, 2014 Author(s): R. J. Thayyen and A. P. Dimri Moisture, temperature and precipitation interplay forced through the orographic processes sustains the Himalayan cryospheric system. However, factors controlling the Slope Environmental Lapse Rate (SELR) of temperature along the higher Himalayan mountain slopes across various glacio-hydrologic regimes remain as a key knowledge gap. Present study dwells on the orographic processes driving the moisture–temperature interplay in the monsoon and cold-arid glacio-hydrological regimes of the Himalaya. Systematic data collection at three altitudes between 2540 and 3763 m a.s.l. in the Garhwal Himalaya (hereafter called monsoon regime) and between 3500 and 5600 m a.s.l. in the Ladakh Himalaya (herefater called cold-arid regime) revealed moistrue control on temperature distribution at temporal and spatial scales. Observed daily SELR of temperature ranges between 9.0 to 1.9 °C km −1 and 17.0 to 2.8 °C km −1 in the monsoon and cold-arid regimes respectively highlighting strong regional variability. Moisture influx to the region, either from Indian summer monsoon (ISM) or from Indian winter monsoon (IWM) forced lowering of SELR. This phenophena of "monsoon lowering" of SELR is due to the release latent heat of condensation from orographically focred lifted air parcel. Seasonal response of SELR in the monsoon regime is found to be closly linked with the variations in the local lifting condensation levels (LCL). Contrary to this, cold-arid system is characterised by the extremely high values of daily SELR upto 17 °C km −1 signifying the extremely arid conditions prevailing in summer. Distinctly lower SELR devoid of monsoon lowering at higher altitude sections of monsoon and cold-arid regimes suggests sustained wetter high altitude regimes. We have proposed a SELR model for both glacio-hydrological regimes demostrating with two sections each using a derivative of the Clausius–Clapeyron relationship by deriving monthly SELR indices. It has been proposed that the manifestations of presence or absence of moisture is the single most important factor determining the temperature distribution along the higher Himalayan slopes driven by the orographic forcings. This work also suggests that the arbitary use of temperature lapse rate to extrapolate temperature to the higher Himalaya is extremely untenable.

Beschreibung: A model study of Abrahamsenbreen, a surging glacier in northern Spitsbergen The Cryosphere Discussions, 8, 5687-5726, 2014 Author(s): J. Oerlemans and W. J. J. van Pelt The climate sensitivity of Abrahamsenbreen, a 20 km long surge-type glacier in northern Spitsbergen, is studied with a simple glacier model. A scheme to describe the surges is included, which makes it possible to account for the effect of surges on the total mass budget of the glacier. A climate reconstruction back to AD 1300, based on ice-core data from Lomonosovfonna and climate records from Longyearbyen, is used to drive the model. The model is calibrated by requesting that it produces the correct Little Ice Age maximum glacier length and simulates the observed magnitude of the 1978-surge. Abrahamsenbreen is strongly out of balance with the current climate. If climatic conditions will remain as they were for the period 1989–2010, the glacier will ultimately shrink to a length of about 4 km (but this will take hundreds of years). For a climate change scenario involving a 2 m yr −1 rise of the equilibrium line from now onwards, we predict that in the year 2100 Abrahamsenbreen will be about 12 km long. The main effect of a surge is to lower the mean surface elevation and to increase the ablation area, thereby causing a negative perturbation of the mass budget. We found that the occurrence of surges leads to a somewhat stronger retreat of the glacier in a warming climate. Because of the very small bed slope, Abrahamsenbreen is sensitive to small perturbations in the equilibrium-line altitude E . For a decrease of E of only 160 m, the glacier would steadily grow into the Woodfjorddalen until after 2000 years it would reach the Woodfjord and calving could slow down the advance.

Beschreibung: Comparison of aeolian snow transport events and snow mass fluxes between observations and simulations made by the regional climate model MAR in Adélie Land, East Antarctica The Cryosphere Discussions, 8, 6007-6032, 2014 Author(s): A. Trouvilliez, H. Gallée, F. Naaim-Bouvet, C. Genthon, C. Amory, V. Favier, C. Agosta, L. Piard, and H. Bellot The regional climate model MAR including a coupled snow pack/aeolian snow transport parameterisation is compared with aeolian snow mass fluxes at a fine spatial resolution (5 km horizontally and 2 m vertically) and at a fine temporal resolution (30 min) over 1 month in Antarctica. Numerous feedbacks are taken into account in the MAR including the drag partitioning caused by the roughness elements. Wind speed is correctly simulated with a positive value of the Nash test (0.60 and 0.37) but the wind speeds above 10 m s −1 are underestimated. The aeolian snow transport events are correctly reproduced with a good temporal resolution except for the aeolian snow transport events with a particles' maximum height below 1 m. The simulated threshold friction velocity, calculated without snowfall, is overestimated. The simulated aeolian snow mass fluxes between 0 to 2 m have the same variations but are underestimated compared to the second-generation FlowCapt values and so is the simulated relative humidity at 2 m. This underestimation is not entirely due to the underestimation of the simulated wind speed. The MAR underestimates the aeolian snow quantity that pass through the first two meters by a factor ten compared to the second-generation FlowCapt value (13 990 kg m −1 and 151 509 kg m −1 respectively). It will conduct the MAR, with this parametrisation, to underestimate the effect of the aeolian snow transport on the Antarctic surface mass balance.

Beschreibung: Influence of weak layer heterogeneity and slab properties on slab tensile failure propensity and avalanche release area The Cryosphere Discussions, 8, 6033-6057, 2014 Author(s): J. Gaume, G. Chambon, N. Eckert, M. Naaim, and J. Schweizer Dry-snow slab avalanches are generally caused by a sequence of fracture processes including failure initiation in a weak snow layer underlying a cohesive slab followed by crack propagation within the weak layer (WL) and tensile fracture through the slab. During past decades, theoretical and experimental work has gradually improved our knowledge of the fracture process in snow. However, our limited understanding of crack propagation and fracture arrest propensity prevents the evaluation of avalanche release sizes and thus impedes hazard assessment. To address this issue, slab tensile failure propensity is examined using a mechanically-based statistical model of the slab–WL system based on the finite element method. This model accounts for WL heterogeneity, stress redistribution by elasticity of the slab and the slab possible tensile failure. Two types of avalanche release are distinguished in the simulations: (1) full-slope release if the heterogeneity is not sufficient to stop crack propagation and to trigger a tensile failure within the slab, (2) partial-slope release if fracture arrest and slab tensile failure occurs due to the WL heterogeneity. The probability of these two release types is presented as a function of the characteristics of WL heterogeneity and of the slab. One of the main outcomes is that, for realistic values of the parameters, the tensile failure propensity is mainly influenced by slab properties. Hard and thick snow slabs are more prone to wide-scale crack propagation and thus lead to larger avalanches (full-slope release). In this case, the avalanche size is mainly influenced by topographical and morphological features such as rocks, trees, slope curvature and the spatial variability of the snow depth as it is often claimed in the literature.

Beschreibung: Climatic signals from 76 shallow firn cores in Dronning Maud Land, East Antarctica The Cryosphere Discussions, 8, 5961-6005, 2014 Author(s): S. Altnau, E. Schlosser, E. Isaksson, and D. Divine The spatial and temporal distribution of surface mass balance (SMB) and δ 18 O were investigated in the first comprehensive study of a set of 76 firn cores retrieved by various expeditions during the past three decades in Dronning Maud Land, East Antarctica. The large number of cores was used to calculate stacked records of SMB and δ 18 O, which considerably increased the signal-to-noise ratio compared to earlier studies and facilitated the detection of climatic signals. Considerable differences between cores from the interior plateau and the coastal cores were found. The δ 18 O of both the plateau and the ice shelf cores exhibit a slight positive trend over the second half of the 20th century. In the corresponding period, the SMB has a negative trend in the ice shelf cores, but increases on the plateau. Comparison with meteorological data from Neumayer Station revealed that for the ice shelf regions atmospheric dynamic effects are more important than thermodynamics, while on the plateau, the temporal variations of SMB and δ 18 O occur mostly in parallel, thus can be explained by thermodynamic effects. The Southern Annular Mode (SAM) exhibits a positive trend since the mid-1960s, which is assumed to lead to a cooling of East Antarctica. This is not confirmed by the firn core data in our data set. Changes in the atmospheric circulation that result in a changed seasonal distribution of precipitation/accumulation could partly explain the observed features in the ice shelf cores.

Beschreibung: Brief Communication: Light-absorbing impurities can reduce the density of melting snow The Cryosphere Discussions, 8, 259-271, 2014 Author(s): O. Meinander, A. Kontu, A. Virkkula, A. Arola, L. Backman, P. Dagsson-Waldhauserová, O. Järvinen, T. Manninen, J. Svensson, G. de Leeuw, and M. Leppäranta Climatic effects of Black Carbon (BC) deposition on snow have been proposed to result from reduced snow albedo and increased melt due to light-absorbing particles. In this study, we hypothesize that BC may decrease the liquid water retention capacity of melting snow, and present our first data, where both the snow density and elemental carbon content were measured. In our experiments, artificially added light-absorbing impurities decreased the density of seasonally melting natural snow. We also suggest three possible processes that might lead to the lower snow density.