ALBERT

Beschreibung: The South Shetland Islands are located at the northern tip of the Antarctic Peninsula (AP). This region was subject to extreme warming trends in the atmospheric surface layer. Surface air temperature increased about 3K in 50 years, concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. The positive trend in surface air temperature has currently come to a halt. Observed surface air temperature lapse rates show a high variability during 5 winter months (standard deviations up to 1:0K=100m), and a distinct spatial heterogeneity reflecting the impact of synoptic weather patterns. The increased mesocyclonic activity during the winter time over the past decades in the study area results in intensified advection of warm, moist air with high temperatures and rain, and leads to melt conditions on the ice cap, fixating surface air temperatures to the melting point. Its impact on winter accumulation results in the observed negative mass balance estimates. Six years of continuous glaciological measurements on mass balance stake 10 transects as well as five years of climatological data time series are presented and a spatially distributed glacier energy balance melt model adapted and run based on these multi-year data sets. The glaciological model is generally in good agreement, except for climatic conditions promoting snow drift by high wind speeds, turbulence-driven snow deposition and snow layer erosion by rain. No drift can be seen over the course of the 5-year model run period. The winter accumulation does not suffice to compensate for the high variability in summer ablation. The results are analyzed to assess changes in melt water input to 15 the coastal waters, specific glacier mass balance and the equilibrium line altitude. The Fourcade Glacier catchment drains into Potter cove, has an area of 23.6 km2 and is to 93.8% glacierized. Annual discharge from Fourcade Glacier into Potter Cove is estimated to q = (25 pm 6) hm3/yr with the standard deviation of 8% annotating the high interannual variability. Published studies suggest rather stable conditions of slightly negative glacier mass balance until the mid 80's with an ELA of approx. 150 m. The average equilibrium line altitude (ELA) calculated from own glaciological observations on Fourcade Glacier over the time period 2010 to 2015 amounts to ELA = (260 pm 20) m. The calculated accumulation area ratio suggests dramatic changes in the future extension of the inland ice cap for the South Shetland Islands.

Beschreibung: The South Shetland Islands are located at the northern tip of the AP which is among the fastest warming regions on Earth. The islands are especially vulnerable to climate change due to their exposure to transient low-pressure systems and their maritime climate. Surface air temperature increases (2.5K in 50 years) are concurrent with retreating glacier fronts, an increase in melt areas, ice surface lowering and rapid break-up and disintegration of ice shelves. We have compiled a unique meteorological data set for the King George Island (KGI)/Isla 25 de Mayo, the largest of the South Shetland Islands. It comprises high-temporal resolution and spatially distributed observations of surface air temperature, wind directions and wind velocities, as well as glacier ice temperatures in profile with a fully equipped automatic weather station on the Warszawa Icefield, from November 2010 and ongoing. In combination with two long-term synoptic datasets (40 and 10 years, respectively) and NCEP/NCAR reanalysis data, we have looked at changes in the climatological drivers of the glacial melt processes, and the sensitivity of the inland ice cap with regard to winter melting periods and pressure anomalies. The analysis has revealed‚ a positive trend of 5K over four decades in minimum surface air temperatures for winter months, clearly exceeding the published annual mean statistics, associated to a decrease in mean monthly winter sea level pressure. This concurs with a positive trend in the Southern Annular Mode (SAM) index, which gives a measure for the strength and extension of the Antarctic vortex. We connect this trend with a higher frequency of low-pressure systems hitting the South Shetland Islands during austral winter, bringing warm and moist air masses from lower latitudes. Due to its exposure to the impact of transient synoptic weather systems, the ice cap of KGI is especially vulnerable to changes during winter glacial mass accumulation period. A revision of seasonal changes in adiabatic air temperature lapse rates and their dependency on exposure and elevation has shown a clear decoupling of atmospheric surface layers between coastal areas and the higher-elevation ice cap, showing the higher sensitivity to free atmospheric flow and synoptic changes. Observed surface air temperature lapse rates show a high variability during winter months (standard deviations up to ±1.0K/100 m), and a distinct spatial variability reflecting the impact of synoptic weather patterns. The observed advective conditions bringing warm, moist air with high temperatures and rain, lead to melt conditions on the ice cap, fixating surface air temperatures to the melting point. This paper assesses the impact of large-scale atmospheric circulation variability and climatic changes on the atmospheric surface layer and glacier mass accumulation of the upper ice cap during winter season for the Warszawa Icefield on KGI.

Beschreibung: During the summer field campaigns within the period November 2010 to March 2013, intensive repeat measurements with Differential GPS (DGPS) at static points of the mass balance stakes as well as kinematic tracks along a grid covering Fourcade and Polar Club glaciers on the Potter Peninsula and the Bellinghausen Dome on the Fieldes Peninsula were carried out. Data was gridded and interpolated to come up with a more exact topography (digital elevation model) for the area of investigation. Data was used to assess glacier velocities. Kinematic tracks were gridded and interpolated to come up with a more exact topography (digital elevation model) for the area of investigation. The data also serves as ground truthing for georeferencing of satellite imagery data by providing exact position coordinates of distinct land marks.