Halocline Layer (Arctic)

The Arctic halocline is the salinity-stratified layer that separates the cold, fresh surface mixed layer from the warm, salty Atlantic Water below in the Arctic Ocean. Salinity rises sharply with depth across roughly 50 to 200 meters while temperature stays near freezing, so density is controlled by salt, not heat. This cold halocline insulates the sea-ice cover from the Atlantic heat at depth, limiting upward heat flux to the ice base. It is maintained by river runoff, sea-ice melt, and brine rejection during freeze-up. Weakening or shoaling of the halocline lets more deep heat reach the surface, accelerating sea-ice loss in a process sometimes called Atlantification.