Variabilität der rezenten Akkumulationsrate im küstennahen Dronning Maud Land, Antarktis

Abstract

In light of possible future sea-level change, investigation of surface-mass balance of the polar ice sheets has become amajor concern of glaciological research. Yet Antarctica's total surface-mass balance is still not accurately determined, making up for the largest uncertainties of predictions regarding sea-level rise in the 21st century.This study contributes new data sets of recent snow-accumulation rates and provides insight in local features affecting the small-scale distribution of accumulation.The aim of the work is to establish a detailed picture of spatial accumulation variability on the scale of some tens of kilometers and of temporal behaviour on interannual to decadal scales. To this end, high-frequency ground-penetrating radar profiling and analyses of shallow firn cores have been utilized. The area of investigation focuses on coastal regions of Dronning Maud Land, East Antarctica, which are likewise in the focus of new satellite missions. The coastal regions are susceptible to global climate change but the local to regional-scale variability of accumulation is not well addressed by general circulationmodels or regional climate models, thus making it necessary to obtain and analyze field data.The accumulation rates on Potsdam Glacier in the coastal part of central Dronning Maud Land have been found to show an undulating pattern, exhibiting a one-fold standard deviation of nearly 50 % around a mean value of some140 kg m-2a-1 for the time period 1970-2004. Temporal variations on decadal scales obtained from the area-wide mean values are only a few per cent, but inter-annual variations derived from dated firn cores are high, showing values between 30-40 % of the core means. Statistical analysis of spatial accumulation series reveals a high periodicity of these undulations with a wavelength of 5~km and amplitudes of 10 m, leading to the conclusion that the features are similar to the megadunes known from the polar plateau, although they lack the spatial extent and the extreme snow morphology of the latter. Thus, the features are likely explicable by a feedback system between atmosphere and cryosphere.The presence of dune-like features as those revealed by this study has implications for firn-core drilling at these coastal sites and for remote sensing of ice-mass changes.Another test site in western Dronning Maud Land, near Kottasberge at the foot of the polar plateau, shows less spatial variability, only 5-10 % around a mean value of 190 kg m-2 a-1 (1980-2005),yet the temporal variations are higher with values of 16 % on decadal scales and likewise about 30 % on interannual scales obtained from firn cores.Comparing spatial and temporal variations on an along-flow radar profile reveals a weak correlation, which is likewise found for the corresponding radar profile on Potsdam Glacier. This observation indicates that the largest temporal differences on decadal scales tend tooccur where spatial variability on the scales of some hundreds of meters to several kilometers is highest.The results presented here are valuable for the validation of satellite-derived ice-mass changes, which are usually averaged over several hundreds of kilometers and do not capture small-scale variability. Spatial variations in accumulation rates as those reported from Potsdam Glacier are likely sensed by gravity missions like GRACE, emphasizing the necessity of ground-truthing, asprovided by this study