Weakening of Cold Halocline Layer Exposes Sea Ice to Oceanic Heat in the Eastern Arctic Ocean

A 15-yr duration record of mooring observations from the eastern (>70 degrees E) Eurasian Basin (EB) of the Arctic Ocean is used to show and quantify the recently increased oceanic heat flux from intermediate-depth (similar to 150-900m) warmAtlantic Water (AW) to the surfacemixed layer and sea ice. The upward release ofAWheat is regulated by the stability of the overlying halocline, which we show has weakened substantially in recent years. Shoaling of theAWhas also contributed, with observations in winter 2017-18 showing AWat only 80m depth, just below the wintertime surfacemixed layer, the shallowest in our mooring records. The weakening of the halocline for several months at this time implies that AW heat was linked to winter convection associated with brine rejection during sea ice formation. This resulted in a substantial increase of upward oceanic heat flux during the winter season, froman average of 3-4W m(-2) in 2007-08 to.10Wm(-2) in 2016-18. This seasonalAWheat loss in the easternEBis equivalent to a more than a twofold reduction of winter ice growth. These changes imply a positive feedback as reduced sea ice cover permits increased mixing, augmenting the summer-dominated ice-albedo feedback.