An Edge-Referenced Surface Fresh Layer in the Seasonal Ice Zone

Seasonal Ice Zone Reconnaissance Surveys (SIZRS) of the Beaufort Sea aboard U.S. Coast Guard Arctic Domain Awareness flights were made monthly from June to October, 2012 to 2015. The seasonal ice zone (SIZ), where ice melts and reforms annually, encompasses the marginal ice zone (MIZ). Thus SIZRS tracks interannual MIZ conditions, providing a regional context for smaller-scale MIZ processes.

Observations with Air eXpendable CTDs (AXCTDs) reveal a salinity pattern associated with large-scale gyre circulation as well as the seasonal formation of a 20m-deep fresh layer relative to the ice edge. Repeat occupations of the SIZRS lines from 72°N to 76°N on 140°W and 150°W allow us to relate observed hydrography to atmospheric indices. Using this relationship, we separate basin-wide salinity signals from the fresh layer associated with the ice edge. While this layer extends under the ice edge as the melt season progresses, its presence is independent of year and absolute latitude north. Within this fresh layer, we correlate average salinity to distance from the ice edge.

To test a formation mechanism for this layer, a 1-D Price-Weller-Pinkel (PWP) model adapted for ice-covered seas simulates mixing processes in the top 100 meters of the ocean. Surface forcing fluxes are taken from the Marginal Ice Zone Modeling and Assimilation System (MIZMAS). PWP output supports local formation of the layer by ice melt. This layer may have implications for the behavior of freshwater in the Beaufort Gyre as the local SIZ grows and persists.