Description: The drift of 52 icebergs tagged with GPS buoys in the Weddell Sea since 1999 has been investigated with respect to prevalent drift tracks, sea ice/iceberg interaction, and freshwater fluxes. Buoys were deployed on small- to medium-sized icebergs (edge lengths 〈= 5 km) in the southwestern and eastern Weddell Sea. The basin-scale iceberg drift of this size class was established. In the western Weddell Sea, icebergs followed a northward course with little deviation and mean daily drift rates up to 9.5 ± 7.3 km/d. To the west of 40°W the drift of iceberg and sea ice was coherent. In the highly consolidated perennial sea ice cover of 95% the sea ice exerted a steering influence on the icebergs and was thus responsible for the coherence of the drift tracks. The northward drift of buoys to the east of 40°W was interrupted by large deviations due to the passage of low-pressure systems. Mean daily drift rates in this area were 11.5 ± 7.2 km/d. A lower threshold of 86% sea ice concentration for coherent sea ice/iceberg movement was determined by examining the sea ice concentration derived from Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer for EOS (AMSR-E) satellite data. The length scale of coherent movement was estimated to be at least 200 km, about half the value found for the Arctic Ocean but twice as large as previously suggested. The freshwater fluxes estimated from three iceberg export scenarios deduced from the iceberg drift pattern were highly variable. Assuming a transit time in the Weddell Sea of 1 year, the iceberg meltwater input of 31 Gt which is about a third of the basal meltwater input from the Filchner Ronne Ice Shelf but spreads across the entire Weddell Sea. Iceberg meltwater export of 14.2 × 103 m3 s-1, if all icebergs are exported, is in the lower range of freshwater export by sea ice.

Description: During Ice Station POLarstern (ISPOL; R.V. Polarstern cruise ANT XXII/2, November 2004-January 2005), hydrographic and tracer observations were obtained in the western Weddell Sea while drifting closely in front of the Larsen Ice Shelf. These observations indicate recently formed Weddell Sea Bottom Water, which contains significant contributions of glacial melt water in its upper part, and High-Salinity Shelf Water in its lower layer. The formation of this bottom water cannot be related to the known sources in the south, the Filchner-Ronne Ice Shelf. We show that this bottom water is formed in the western Weddell Sea, most likely in interaction with the Larsen C Ice Shelf. By applying an Optimum Multiparameter Analysis (OMP) using temperature, salinity, and noble gas observations (helium isotopes and neon), we obtained mean glacial melt-water fractions of about 0.1% in the bottom water. On sections across the Weddell Gyre farther north, melt-water fractions are still on the order of 0.04%. Using chlorofluorocarbons (CFCs) as age tracers, we deduced a mean transit time between the western source and the bottom water found on the slope toward the north (9±3 years). This transit time is larger and the inferred transport rate is small in comparison to previous findings. But accounting for a loss of the initially formed bottom water volume due to mixing and renewal of Weddell Sea Deep Water, a formation rate of 1.1±0.5 Sv in the western Weddell Sea is plausible. This implies a basal melt rate of 35±19 Gt/year or 0.35±0.19 m/year at the Larsen Ice Shelf. This bottom water is shallow enough that it could leave the Weddell Basin through the gaps in the South Scotia Ridge to supply Antarctic Bottom Water. These findings emphasize the role of the western Weddell Sea in deep- and bottom-water formation, particularly in view of changing environmental conditions due to climate variability, which might induce enhanced melting or even decay of ice shelves.

Description: It has been proposed that huge ice shelves might face less basal melting in a warmer climate due to less sea ice formation on the continental shelf and thus a reduced density gradient between ice shelf front and the cavern interior. We present the results of a 100-year simulation with BRIOS-2.2 forced with the ECHAM5-MPIOM output for the IPCC-A1B scenario. The results show that basal melting enhances for all ice shelves, but the enhancement is minor for huge ice shelves like Filchner-Ronne and Ross while the smaller ones like Fimbulisen and Getz are threatened by an up to 100% increase. Further analysis reveals that a decrease in salinity (due to a reduced sea ice cover) in parallel to slightly higher temperatures on the broad continental shelves are responsible for a mitigated response of the huge ice shelves to climate warming. In contrast, minor decreases in salinity in combination with increased near-bottom temperatures on the narrow continental shelves cause smaller ice shelves to be highly vulnerable to a warmer climate.

Description: Antarctic marginal seas are the warm tub for the floating extensions of the Antarctic ice sheet. The analysis of a 200-year (1900--2099) integration of a regional ice-ocean model (BRIOS-2.2) forced with the atmospheric output of an IPCC-20C3M scenario simulation with the coupled atmosphere-sea ice-ocean ECHAM5-MPIOM reveals that these seas exhibit significant decadal variability. Changes in bottom salinity on the southern Weddell Sea continental shelf, caused by a variable sea ice cover and related modification of surface waters near the Greenwich Meridian, influence the circulation such that cold waters from the Weddell Sea flush into the southeast Pacific Ocean with varying intensity. The deep temperature signal propagates westward and onto the continental shelves of the Amundsen and Ross Seas. Weddell Sea anomalies thus could be a new aspect to consider at the present search for mechanisms controlling the flow of warmer deep waters towards the floating extensions of the West Antarctic Ice Sheet.