Drivers of Interannual Sea Ice Concentration Variability in the Atlantic Water Inflow Region North of Svalbard. Issue 4 (28th April 2021) - Lundesgaard, Øyvind
Abstract: Sea ice concentration along the continental margin of the Arctic Ocean is influenced by a multitude of factors, including local freezing and melting due to atmospheric forcing, lateral advection of sea ice by winds and ocean currents, and melting from below by warm Atlantic Water (AW). Here, we characterize the evolution of sea ice concentration in an area on the continental shelf break north of Svalbard in the period between 2012 and 2019. During this period, a semi‐regular seasonal pattern in sea ice concentration was interrupted by three anomalous seasons; a high ice anomaly during autumn 2014 and low ice anomalies during spring 2016 and 2018. Neither type of anomaly can be explained by abnormal upper ocean heat content as measured by an ocean mooring located near the shelf break. Instead, we find that the predominant driver of interannual sea ice concentration variability during this period was variations in large‐scale ice drift. While heat flux from the ocean cannot explain the interannual variability, it plays a key role in maintaining periods of open water in the AW inflow region despite freezing air temperatures during most of the year. These results are consistent with the sea ice concentration flux divergence from satellite records, which suggests that the southern continental slope of the Eurasian Basin is an important melting area for sea ice advected in from the north. Plain Language Summary: Atlantic Water flows from the Nordic Seas into the Arctic Ocean, where it forms a warm ocean current running along the continental slope. At the beginning of this current, in the region north of Svalbard, the warm upper ocean maintains the ocean ice‐free during parts of the year where sea ice otherwise would have formed. The goal of this study was to investigate whether years with a particularly large or small amount of ice in this region occur as a result of unusually high or low ocean temperature. We examined records of temperature from instruments moored in the ocean northeast of Svalbard between 2012 and 2019. We compared these observations with the satellite record of sea ice concentration, along with other variables including air temperature and sea ice movement. Our findings suggest that ocean heat strongly influences sea ice concentration by melting ice and preventing new ice from forming, but that large year‐to‐year sea ice variations were not a result of variations in ocean temperature. Instead, unusual sea ice years were associated with unusual large‐scale wind patterns, which in turn control air temperature and moisture and movement of sea ice into the area from other parts of the Arctic Ocean. Key Points: Ocean heat maintains ice‐free conditions in the Atlantic Water inflow region during autumn/winter Interannual sea ice variability was not driven by changes in ocean heat during 2012–2019 Anomalous sea ice years were associated with anomalies in atmospheric circulation and ice advection