Partial recovery of the Arctic Ocean halocline

The evolution during the 1990's of the cold halocline layer (CHL) of the Arctic Ocean is investigated using data from icebreaker and SCICEX submarine cruises. The CHL disappearance and subsequent partial recovery is described along repeated transects through the central Arctic Ocean from the Alpha Ridge to the Nansen Basin. Salinity at the top of the halocline is used as a measure of halocline development, with high salinity corresponding to a poorly developed halocline. In the Nansen, Amundsen, and Makarov basins, upper ocean salinity increased from 1991 to 1998 as the CHL disappeared, then decreased from 1998 to 2000 as it recovered. Salinity was higher over the study region through the 1990's than at any time during the prior 40 year period, hence the 1990's CHL recovery was only partial. Disappearance of the CHL from the Eurasian Basin in the early 1990's was due to a shift from the Laptev to East Siberian seas of the region for seaward flow of low salinity Siberian shelf waters. Ice velocities and sea level pressure fields suggest that the reappearance of the CHL in 1999 corresponded to a shift of this flow back to the Laptev Sea region.