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

Landfast sea ice (fast ice) attached to Antarctic(near-)coastal elements is a critical component of the local physical andecological systems. Through its direct coupling with the atmosphere andocean, fast-ice properties are also a potential indicator of processesrelated to a changing climate. However, in situ fast-ice observations inAntarctica are extremely sparse because of logistical challenges and harshenvironmental conditions. Since 2010, a monitoring program observing theseasonal evolution of fast ice in Atka Bay has been conducted as part of theAntarctic Fast Ice Network (AFIN). The bay is located on the northeasternedge of Ekström Ice Shelf in the eastern Weddell Sea, close to theGerman wintering station Neumayer III. A number of sampling sites have beenregularly revisited each year between annual ice formation and breakup toobtain a continuous record of sea-ice and sub-ice platelet-layer thickness,as well as snow depth and freeboard across the bay.Here, we present the time series of these measurements over the last 9years. Combining them with observations from the nearby Neumayer IIImeteorological observatory as well as auxiliary satellite images enables usto relate the seasonal and interannual fast-ice cycle to the factors thatinfluence their evolution.On average, the annual consolidated fast-ice thickness at the end of thegrowth season is about 2 m, with a loose platelet layer of 4 mthickness beneath and 0.70 m thick snow on top. Results highlight thepredominately seasonal character of the fast-ice regime in Atka Bay withouta significant interannual trend in any of the observed variables over the9-year observation period. Also, no changes are evident when comparingwith sporadic measurements in the 1980s and 1990s. It is shown that strongeasterly winds in the area govern the year-round snow distribution and alsotrigger the breakup of fast ice in the bay during summer months.Due to the substantial snow accumulation on the fast ice, a characteristicfeature is frequent negative freeboard, associated flooding of the snow–iceinterface, and a likely subsequent snow ice formation. The buoyant plateletlayer beneath negates the snow weight to some extent, but snowthermodynamics is identified as the main driver of the energy and massbudgets for the fast-ice cover in Atka Bay.The new knowledge of the seasonal and interannual variability of fast-iceproperties from the present study helps to improve our understanding ofinteractions between atmosphere, fast ice, ocean, and ice shelves in one ofthe key regions of Antarctica and calls for intensified multidisciplinarystudies in this region