ИСТИНА

On the basis of various data sets we traced formation of a ‘dome’- shaped density structure over the Central Bank - an important morphological element of the Barents Sea bottom topography. Horizontal density gradient over the bank maintains an anticyclonic baroclinic vortex around the bank, splitting the Atlantic Water (AW) flow from the west into two branches. There are different opinions on the origin of the dome-shaped structure and on the mechanisms of its maintenance/regeneration. According to the earlier study, based on the 20th century hydrographic data, additional salinization of the water over CB due to freezing is critical, and only in severe winters haline convection leads to surface-to-bottom overturning of the water column over the bank. In the absence of local freezing convection does not reach the seabed, thus preventing formation/regeneration of the dome-shaped structure. Basing on the observational evidence that the AW constitutes a major fraction of the bottom water over CB other authors concluded that atmospheric cooling alone is sufficient for densification of the surface waters, with only minor contribution of freezing. The major conclusion, which follows from our analysis, based on direct winter measurements in 2019, is that under reduced ice cover, transformation of thermohaline structure during the cold season principally differs from that under the ‘normal’ climate conditions in the 20th century. Transition from the stratified vertical structure (in summer) to the homogeneous one (in winter) is governed by thermal convection. Additional input of warm and salty water with inflowing AW is crucial to allow reaching the seabed vertical mixing before the temperature drops to the freezing point. Cascading of dense water from the bank commences as soon as convection has spread to the seabed. The influence of cascading on the Barents Sea hydrographic structure extends far away from the bank. In the absence of advective influx of salt and warm water vertical convection can also reach the seabed. However, under this condition formation of sea ice and haline convection is required. In this case water temperature in the homogeneous water column over the bank is close to the freezing point. Obtained results suggest that in the warmer climate the role of sea ice in winter transformation of thermohaline conditions over the bank is opposite to what it was in the ‘normal’ climate: imported sea ice blocks convection, thus making the water in the dense ‘dome’ warmer than it typically was throughout the 20th century.