Mass Loss of Larsen B Tributary Glaciers (Antarctic Peninsula) Unabated Since 2002

Ice mass loss continues at a high rate among the large glacier tributaries of the Larsen B Ice Shelf following its disintegration in 2002. We evaluate recent mass loss by mapping elevation changes between 2006 and 201011 using differencing of digital elevation models (DEMs). The measurement accuracy of these elevation changes is confirmed by a null test, subtracting DEMs acquired within a few weeks. The overall 2006201011 mass loss rate (9.0 2.1 Gt a-1) is similar to the 2001022006 rate (8.8 1.6 Gt a-1), derived using DEM differencing and laser altimetry. This unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins. On Crane Glacier, the thinning pulse, initially greatest near the calving front, is now broadening and migrating upstream. The largest losses are now observed for the HektoriaGreen glacier basin, having increased by 33 since 2006. Our method has enabled us to resolve large residual uncertainties in the Larsen B sector and confirm its state of ongoing rapid mass loss

The Link Between Climate Warming and Break-Up of Ice Shelves in the Antarctic Peninsula

A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis

Ice Velocity Mapping of Ross Ice Shelf, Antarctica by Matching Surface Undulations Measured by Icesat Laser Altimetry

We present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetrydata from the Ice Cloud and land Elevation Satellite (ICESat; 20032009). The method matches undulations measured at crossover points between successive campaigns

Spectral characterization, radiative forcing and pigment content of coastal Antarctic snow algae: approaches to spectrally discriminate red and green communities and their impact on snowmelt

Here, we present radiative forcing (RF) estimates by snow algae in the Antarctic Peninsula (AP) region from multi-year measurements of solar radiation and ground-based hyperspectral characterization of red and green snow algae collected during a brief field expedition in austral summer&nbsp;2018. Our analysis includes pigment content from samples at three bloom sites. Algal biomass in the snow and albedo reduction are well-correlated across the visible spectrum. Relative to clean snow, visibly green patches reduce snow albedo by &sim;40&thinsp;% and red patches by &sim;20&thinsp;%.&nbsp;However, red communities absorb considerably more light per milligram of pigment compared to green communities, particularly in green wavelengths. Based on our study results, it should be possible to differentiate red and green algae using Sentinel-2 bands in blue, green and red wavelengths. Instantaneous RF averages were double for green (180&thinsp;W&thinsp;m&minus;2) vs. red communities (88&thinsp;W&thinsp;m&minus;2), with a maximum of 228&thinsp;W&thinsp;m&minus;2. Based on multi-year solar radiation measurements at Palmer Station, this translated to a mean daily RF of &sim;26&thinsp;W&thinsp;m&minus;2 (green) and &sim;13&thinsp;W&thinsp;m&minus;2 (red) during peak growing season &ndash; on par with midlatitude dust attributions capable of advancing snowmelt. This results in &sim;2522&thinsp;m3 of snow melted by green-colored algae and &sim;1218&thinsp;m3 of snow melted by red-colored algae annually over the summer, suggesting snow algae play a significant role in snowmelt in the AP regions where they occur. We suggest impacts of RF by snow algae on snowmelt be accounted for in future estimates of Antarctic ice-free expansion in the AP region. The requested paper has a corresponding corrigendum published. Please read the corrigendum first before downloading the article. &nbsp; &nbsp;</p

Influence of Persistent Wind Scour on the Surface Mass Balance of Antarctica

Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (< or = 200 sq km) with reduced surface accumulation. Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones. Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that approx. 2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt /yr in present surface-mass-balance calculations

Oceanic Controls on the Mass Balance of Wilkins Ice Shelf, Antarctica

Several Antarctic Peninsula (AP) ice shelves have lost significant fractions of their volume over the past decades, coincident with rapid regional climate change. Wilkins Ice Shelf (WIS), on the western side of the AP, is the most recent, experiencing a sequence of large calving events in 2008 and 2009. We analyze the mass balance for WIS for the period 1992-2008 and find that the averaged rate of ice-shelf thinning was similar to 0.8 m a(-1), driven by a mean basal melt rate of \u3c w(b)\u3e = 1.3 +/- 0.4 m a(-1). Interannual variability was large, associated with changes in both surface mass accumulation and \u3c w(b)\u3e. Basal melt rate declined significantly around 2000 from 1.8 +/- 0.4 m a(-1) for 1992-2000 to similar to 0.75 +/- 0.55 m a(-1) for 2001-2008; the latter value corresponding to approximately steady-state ice-shelf mass. Observations of ocean temperature T obtained during 2007-2009 by instrumented seals reveal a cold, deep halo of Winter Water (WW; T approximate to - 1.6 degrees C) surrounding WIS. The base of the WW in the halo is similar to 170 m, approximately the mean ice draft for WIS. We hypothesize that the transition in \u3c w(b)\u3e in 2000 was caused by a small perturbation (similar to 10-20 m) in the relative depths of the ice base and the bottom of the WW layer in the halo. We conclude that basal melting of thin ice shelves like WIS is very sensitive to upper-ocean and coastal processes that act on shorter time and space scales than those affecting basal melting of thicker West Antarctic ice shelves such as George VI and Pine Island Glacier

Antarctic ice rises and rumples: Their properties and significance for ice-sheet dynamics and evolution

Locally grounded features in ice shelves, called ice rises and rumples, play a key role buttressing discharge from the Antarctic Ice Sheet and regulating its contribution to sea level. Ice rises typically rise several hundreds of meters above the surrounding ice shelf; shelf flow is diverted around them. On the other hand, shelf ice flows across ice rumples, which typically rise only a few tens of meters above the ice shelf. Ice rises contain rich histories of deglaciation and climate that extend back over timescales ranging from a few millennia to beyond the last glacial maximum. Numerical model results have shown that the buttressing effects of ice rises and rumples are significant, but details of processes and how they evolve remain poorly understood. Fundamental information about the conditions and processes that cause transitions between floating ice shelves, ice rises and ice rumples is needed in order to assess their impact on ice-sheet behavior. Targeted high-resolution observational data are needed to evaluate and improve prognostic numerical models and parameterizations of the effects of small-scale pinning points on grounding-zone dynamics

Ocean variability beneath Thwaites Eastern Ice Shelf driven by the Pine Island Bay Gyre strength

West Antarctic ice-shelf thinning is primarily caused by ocean-driven basal melting. Here we assess ocean variability below Thwaites Eastern Ice Shelf (TEIS) and reveal the importance of local ocean circulation and sea-ice. Measurements obtained from two sub-ice-shelf moorings, spanning January 2020 to March 2021, show warming of the ice-shelf cavity and an increase in meltwater fraction of the upper sub-ice layer. Combined with ocean modelling results, our observations suggest that meltwater from Pine Island Ice Shelf feeds into the TEIS cavity, adding to horizontal heat transport there. We propose that a weakening of the Pine Island Bay gyre caused by prolonged sea-ice cover from April 2020 to March 2021 allowed meltwater-enriched waters to enter the TEIS cavity, which increased the temperature of the upper layer. Our study highlights the sensitivity of ocean circulation beneath ice shelves to local atmosphere-sea-ice-ocean forcing in neighbouring open oceans