Observed atlantification of the Barents Sea Causes the polar front to limit the expansion of winter sea ice

Barents Sea Water (BSW) is formed from Atlantic Water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt. In the eastern Barents Sea, the BSW and fresher, colder Arctic Water meet at the surface along the Polar Front (PF). Despite its importance in setting the northern limit of BSW ventilation, the PF has been poorly documented, mostly eluding detection by observational surveys that avoid seasonal sea ice. In this study, satellite sea surface temperature (SST) observations are used in addition to a temperature and salinity climatology to examine the location and structure of the PF and characterize its variability over the period 1985–2016. It is shown that the PF is independent of the position of the sea ice edge and is a shelf slope current constrained by potential vorticity. The main driver of interannual variability in SST is the variability of the Atlantic Water temperature, which has significantly increased since 2005. The SST gradient associated with the PF has also increased after 2005, preventing sea ice from extending south of the front during winter in recent years. The disappearance of fresh, seasonal sea ice melt south of the PF has led to a significant increase in BSW salinity and density. As BSW forms the majority of Arctic Intermediate Water, changes to BSW properties may have far-reaching impacts for Arctic Ocean circulation and climate.