A new study led by Bjørg Risenbrobakken from the Bjerknes Centre for Climate Research show that increased influx of freshwater to the SW Barents Sea, due to melting of ice, resulted in a well-stratified water column 11,000-9,800 years ago. Cold winters caused refreezing of the fresh surface water, while the sea ice melted and the surface layer warmed up during warm summers. The warm and fresh surface layer maintained a stratified water column throughout the summer season, probably in association with weak wind mixing and strong autumn/winter cooling. Increased transport of ice from the Arctic probably enhanced the influence of ice in the SW Barents Sea during winters. Due to the continual winter sea ice cover and strongly stratified water column, the exchange of gas and heat between ocean and the atmosphere was strongly reduced. Reduced release of heat from the ocean to atmosphere caused bottom water temperatures 1-3°C warmer than today.
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Stable conditions 7,500-2,500 years ago
The present day oceanographic pattern, and the location of the polar front, was gradually established through the early and mid Holocene (the present warm period representing the last 11,000 years). In general, the period 7,500-2,500 years ago was more stable than earlier parts of the Holocene. Surface water summer temperatures decreased, the water column was well mixed during winter, and a low but increasing influence of Atlantic bottom water characterized the SW Barents Sea.
Unstable conditions the last 2,500 years
The last 2,500 years has been characterized by generally unstable conditions. Several episodes have occurred, where the surface and subsurface salinity has been reduced as compared to the present, corresponding with increased deposition of ice rafted material. Through these periods the water column was better stratified than today. The area influenced by coastal water expanded and more sea ice occurred, in association with predominantly stable cold conditions.
The study shows that the amplitude of temperature and salinity variations recorded through the last 11,000 years in general is larger than what has been indicated by instrumental observations during the last 30 years in the same area. A strong year-round stratification has developed occasionally, in contrast to the currently well-mixed water column during winter. The instrumental records thus probably underestimates the possible range of interglacial climate variability in the SW Barents Sea.