Formation of dense shelf water associated with sea ice freezing in the Gulf of Anadyr estimated with oxygen isotopic ratios

Abstract

We analyzed temperature and salinity data and oxygen isotope ratios (δ18O) in summer 2018 in order to quantify the formation of dense shelf water (DSW) associated with sea ice freezing in the Gulf of Anadyr in the northwestern Bering Sea. Salinity and δ18O displayed a strong linear relationship in samples upstream (southwest) of the Gulf of Anadyr. However, in bottom water (>26.5 σθ) in the northern Gulf of Anadyr, where a large polynya is the site of high sea ice production in winter, salinity was clearly higher than in the upstream water, whereas δ18O was in the same range. This deviation is consistent with the formation of sea ice through brine rejection and subsequent DSW formation, causing an increase of salinity without changing δ18O. A mass balance calculation based on these results yielded an estimated production of sea ice equivalent to a thickness 0.7 m, a result that matched an independent estimate of 2018 annual ice production based on satellite data. Even though the winter of 2018 had a historically low sea ice extent in the Bering Sea, including the Gulf of Anadyr, our results indicate continued DSW formation in the Gulf of Anadyr.