Sea Surface Salinity tendencies observed by SMOS in the Beaufort Gyre

Abstract

Recent observational and modelling studies have documented changes in the hydrography of the upper Arctic Ocean, in particular an increase of its liquid freshwater content (e.g., Haine et al. 2015, Proshutinsky et al. 2019, Solomon et al. 2021). The main factors contributing to this freshening are the melting of the Greenland ice sheet and glaciers, enhanced sea-ice melt, an increase of river discharge, increase in liquid precipitation and an increase of Pacific Ocean water influx to the Arctic Ocean through the Bering Strait. A retreating-thinning sea ice cover, and a concomitant warming-freshening upper ocean, have a widespread impact across the whole Arctic system through a large number of feedback mechanisms and interactions also with the atmospheric circulation of the northern hemisphere, having the potential to destabilize the thermo-haline circulation in the Northern Atlantic. An increase of liquid freshwater content has been found over both the Canadian Basin and the Beaufort Sea that can have a large impact on the Arctic marine ecosystem. The importance of monitoring changes in the Arctic freshwater system and its exchange with subarctic oceans has been widely recognized by the scientific communities. Among the key observable variables, ocean salinity is a proxy for freshwater content and allows to monitor increased freshwater from rivers or ice melt, and it sets the upper ocean stratification, which has important implications in water mass formation and heat storage. Changes in the salinity distribution may affect the water column stability and impact the freshwater pathways over the Arctic Ocean. Sea Surface Salinity (SSS) is observed from space with the L-band (1.4GHz) radiometers such as SMOS (ESA, since 2010) and SMAP (NASA, since 2015). However, retrieving SSS in cold waters is challenging, for different factors. Thanks to the ESA funded the ARCTIC+SSS ITT project, we have now a new enhanced Arctic SMOS Sea Surface Salinity product BEC v.31, which has better quality and resolution than the previous high latitude salinity products which permit to better monitor salinity changes, and thus freshwater. In this presentation we will show the first results of the surface salinity tendency analysis done with the new SMOS BEC SSS v3.1 product in the Beaufort Sea, and other Arctic regions during summer for the period from 2011 to 2021. We will compare the results with other model (TOPAZ) and satellite observations (CryoSat and GRACE). Only summer results will be shown since, observations of SSS are feasable only when the ocean is free of ice. This preliminary analysis shows a clear freshening in the sea surface salinity the Beaufort Gyre region from 2012 to 2019