Investigating the Utility and Limitation of SMAP Sea Surface Salinity in Monitoring the Arctic Freshwater System

Sea surface salinity (SSS) plays a critical role in the water cycle. In the Arctic Ocean, SSS responses to river discharge, sea ice melting/freezing and drifting, surface freshwater forcing (precipitation and evaporation), and ocean transport through open straits from/to Pacific and Atlantic oceans. However, in situ SSS data in the Arctic Ocean are very sparse. The L-band microwave radiometer on board of NASA SMAP mission provides salinity measurements since April 2015, at 40 km resolution with global ocean coverage in ~3 days. With improved land/ice correction and RFI detection, SMAP SSS are retrieved in ice-free regions near the river mouth and ice edge. The collocated SMAP SSS and in situ salinity data collected by AXCTD from Ocean Melting Greenland (OMG) 2016 field campaign along Greenland coast show reasonable agreement in revealing the freshening signature, which is not seen in ocean model output. During the open water season (August), SMAP SSS were retrieved in Chukchi Sea (2015), in Prudhoe Bay and East Siberian Sea (2016), and in Kara Sea in both years. The SSS contrast between the two years is consistent with sea ice concentration observations. Variability of SSS in Kara Sea is correlated positively with adjacent river discharges but negatively with the salinity of water transported from Atlantic Ocean.