Weddell Sea Polynya analysis using SMOS-SMAP Sea Ice Thickness Retrieval

Abstract. The Weddell Sea Polynya is an anomalous large opening in the Antarctic sea ice above the Maud Rise seamount. After 40 years of absence, it fully opened again on 13 September, 2017, and lasted until melt; staying open for a total of 80 days. 2017, however, actually was not the only year the imprint of the polynya could be identified. By investigating sea ice thickness (SIT) data retrieved from the satellite microwave sensors Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP), we have isolated an anomaly of thin sea ice spanning an area comparable to the polynya of 2017 over Maud Rise occurring in September 2018. In this paper, we look at sea ice above Maud Rise in August and September of 2017 and 2018 as well as all years from 2010 until 2020 in a 11-year time series. Using the ERA5 surface wind reanalysis data, we present the strong impact storm activity has on sea ice and help consolidate the theory that the Weddell Sea Polynya, in addition to oceanographic effects, is subject to direct atmospheric forcing. Based on the results presented we propose that the Weddell Sea Polynya, rather than being a binary system with one principal cause, is a dynamic process caused by various different preconditioning factors that must occur simultaneously for it to occur. Moreover, we show that rather than an abrupt stop to anomalous activity atop Maud Rise in 2017, the very next year shows signs of polynya-favourable activity that, although insufficient, was present in the region. This effect, as will be shown in the 11-year SMOS record, is not unique to 2018 and similar anomalies are identified in 2010, 2013 and 2014. It is demonstrated that L-band microwave radiometry from the SMOS and SMAP satellites can provide additional useful information, which helps to better understand dynamic sea ice processes like polynya events, in comparison to if satellite sea ice concentration products would be used alone.