Description: The Arctic is undergoing rapid transformations that have brought the Arctic Ocean to the top of international political agendas. Predicting future conditions of the Arctic Ocean system requires scientific knowledge of its present status as well as a process-based understanding of the mechanisms of change. The Arctic in Rapid Transition (ART) initiative is an integrative, international, interdisciplinary pan-Arctic program to study changes and feedbacks among the physical and biogeochemical components of the Arctic Ocean and their ultimate impacts on biological productivity. The goal of ART is to develop priorities for Arctic marine science over the next decade. Three overarching questions form the basis of the ART science plan: (1) How were past transitions in sea ice connected to energy flows, elemental cycling, biological diversity and productivity, and how do these compare to present and projected shifts? (2) How will biogeochemical cycling respond to transitions in terrestrial, gateway and shelf-to-basin fluxes? (3) How do Arctic Ocean organisms and ecosystems respond to environmental transitions including temperature, stratification, ice conditions, and pH? The integrated approach developed to answer the ART key scientific questions comprises: (a) process studies and observations to reveal mechanisms, (b) the establishment of links to existing monitoring programs, (c) the evaluation of geological records to extend time-series, and (d) the improvement of our modeling capabilities of climate-induced transitions. In order to develop an implementation plan for the ART initiative, an international and interdisciplinary workshop is currently planned to take place in Winnipeg, Canada in October 2010.

Description: The glacial history of the Antarctic Ice Sheet in the Weddell Sea embayment during the Last Glacial Maximum (LGM; 23-19 ka) is a matter of debate. Existing onshore and offshore data suggest two alternative reconstructions for the LGM ice sheet extent. One scenario shows an ice sheet grounding line that had advanced to (or at least close to) the shelf edge throughout the Weddell Sea, embayment. The other reconstruction concludes that the grounding line in the two main cross shelf troughs was located only slightly farther offshore than today. Here we present new data from multibeam swath bathymetry surveys, acoustic sub-bottom profiles and sediment cores collected during recent and past British and German marine expeditions. These data provide new constraints on the glacial history of the eastern part of the Weddell Sea embayment. A previously unknown, stacked grounding zone wedge discovered in the outer shelf part of Filchner Trough possibly marks the northernmost position of the LGM grounding line within this palaeo-ice stream trough. Crescentic moraines and a predominantly smooth seabed morphology mapped north of the Brunt Ice Shelf reveal a complex glacial history with repeated advances of grounded ice or episodic retreats, controlled by a hard seafloor substrate. We will compare new radiocarbon dates obtained from the sediment cores to existing chronologies and use them to reconstruct the timing of the last maximum ice sheet advance and post-LGM retreat. Finally, we will set our new findings into context with results from ice sheet models and discuss their implications for Antarctica's contribution to global meltwater pulses during the last deglaciation.