Seasonal and Interannual Variability of the Upper Mixed Layer Properties in the Barents Sea

Abstract— The rapid changes in the ice and hydrological regimes of the Barents Sea that occurred in the 2000s–2010s determined the objective of this article: to quantitatively assess the seasonal and interannual variability of the relative contributions of processes at the air–sea boundary and in the water column to changes in the thermohaline parameters of the upper mixed layer, which ultimately determine the intra- and interannual dynamics of the ice cover. The study used hydrological and ice data from the GLORYS12v1 global ocean reanalysis system and data on the heat balance components at the ocean surface from the ERA-5 global atmospheric reanalysis. The study found that the dominant contribution to the formation of intraannual variability of the mixed layer temperature is made by heat transfer with the atmosphere (more than 50%) and horizontal advection, smoothing out changes in the temperature of the upper mixed layer: heating in the warm season and cooling in the cold season. The intraannual variability of salinity is controlled by ice melting in the warm season and horizontal advection in the cold season. The increase in salinity due to winter ice formation is significantly less than the freshening caused by summer ice melting. Stable positive trends of varying intensity are observed in the temperature and salinity of the upper mixed layer. These trends are associated with a gradual reduction in ice cover, which ensures an increase in the effectiveness of positive feedback on a seasonal scale, due to which the heating of the upper mixed layer by the end of the warm season exceeds cooling in the subsequent cold season, and freshening in the warm season does not compensate for salinization in the subsequent cold season.