Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020.

In the Arctic Ocean, the “halocline” is a cold near-surface layer where salinity increases rapidly with depth. The halocline isolates the sea ice at the surface from the heat stored in
the underlying warm and salty water. Hence, the strength of the halocline is a key feature in the maintenance
of the sea ice cover. In this study, we use various ocean measurements and computer models to document recent changes in the halocline in the East-Amerasian sector of the Arctic. In this region, warm and salty water, usually found about a hundred meters deep, was found to become closer to the surface from 2012 onwards.

We show that the shoaling of this warm water contributed to the progressive warming and weakening of the halocline in the East-Amerasian Arctic Ocean. This weakening of the halocline is emblematic of the emergence of a new Arctic regime, previously observed in the Eurasian sector of the Arctic, a region undergoing the growing influence from the Atlantic Ocean. Our study suggests the progression of this new regime, with shallow warm water and weakened halocline, further into the Arctic.