Seasonal and interannual variability of landfast sea ice in Atka Bay, Weddell Sea, Antarctica

• Main Authors: Arndt, Stefanie, Hoppmann, Mario, Schmithüsen, Holger, Fraser, Alexander D., Nicolaus, Marcel
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; The Antarctic; Weddell Sea; Neumayer; Neumayer Station; Weddell; Atka; Ekström Ice Shelf; Antarc*; Antarctica; Ice Shelf; Ice Shelves; Sea ice
• Online Access: https://doi.org/10.5194/tc-2019-293; https://tc.copernicus.org/preprints/tc-2019-293/

Landfast sea ice (fast ice), attached to Antarctic coastal and near-coastal elements, is a critical element of the local physical and ecological systems. Through its direct coupling with the atmosphere and ocean, fast ice and its snow cover are also potential indicators of processes related to climate change. However, in-situ fast-ice observations in Antarctica are extremely sparse because of logistical challenges. Since 2010, a monitoring program, which is part of the Antarctic Fast Ice Network (AFIN), has been conducted on the seasonal evolution of fast ice of Atka Bay. The bay is located on the north-eastern edge of Ekström Ice Shelf in the eastern Weddell Sea, close to the German wintering station Neumayer Station III. A number of sampling sites have been regularly revisited between annual ice formation and breakup each year to obtain a continuous record of snow depth, freeboard, sea-ice- and sub-ice platelet layer thickness across the bay. Here, we present the time series of these measurements over the last nine years. Combining them with observations from the nearby meteorological observatory at Neumayer Station as well as satellite images allows to relate the seasonal and interannual fast-ice cycle to the factors that influence its evolution. On average, the annual consolidated fast-ice thickness at the end of the growth season is about two meters, with a loose platelet layer accumulation of four meters beneath and 0.70 meters snow on top. Results highlight the predominately seasonal character of the fast-ice regime in Atka Bay without a significant trend in any of the observed variables over the nine-year observation period. Also, no changes are evident when comparing with measurements in the 1980s. However, strong easterly winds in the area govern the year-round snow redistribution and also trigger the breakup event in the bay during summer months. Due to the substantial snow accumulation on the ice, a characteristic feature is frequent negative freeboard, associated flooding of the snow/ice interface and subsequent formation of snow ice. The buoyant platelet-ice layer beneath negates the snow weight to some extent, but snow thermodynamics is identified as the main driver of the energy and mass budgets for the fast-ice cover in Atka Bay. An enhanced knowledge on the seasonal and interannual variability of the fast-ice properties will improve our understanding of interactions between atmosphere, fast ice, ocean and ice shelves in one of the key regions of Antarctica.