Известия ТИНРО (Sep 2019)
BERING SEA: 2018 AS THE EXTREME LOW-ICE AND WARM YEA
Abstract
Phenomenon of anomalous oceanographic conditions in the Bering Sea in 2018 is considered, with heightened air and water temperature and very low ice cover, as well as its consequences for the water structure, circulation, and chemical properties. These extreme conditions were formed on the background of warming tendency observed in the Bering Sea since 2014, but they were exceptional even relative to this background: deflections of some parameters from their normal values exceeded the standard deviations more than twice (> 2s). The main reason for such conditions was the southern winds prevalence over the entire Sea in winter, in opposite to usual regime when the southern winds blew over its southeastern part only; another factor was strengthened advection of the oceanic waters, still abnormally warm after the period of extreme warming in the North-East Pacific in 2014–2016. As the result, the ice cover in winter and spring was more than twice lower the normal values, the air and water temperatures through the year were above their normal values in 15 and 5 degrees Celsius, respectively. The winter convection was weakened that caused deepening of the cold subsurface layer core and prevented forming of the cold near-bottom water masses on the shelf that was usual for the Bering Sea. Under this considerable redistribution of the water density coupled with unusual wind regime, the water circulation changed, in particular in the northern Bering Sea where the Navarin Current were weakened or even absent and the northward water transport was realized through the eastern shelf delivering to the northern shelf and Bering Strait the coastal waters from Alaska instead of the deep-water basins waters, as usually. Strong advection of the oceanic waters through the Aleutian Straits promoted growth of nutrients concentrations and lowering of oxygen content in the intermediate layer of the Bering Sea. These extreme oceanographic conditions in the Bering Sea in 2018 were statistical outliers, atypical even for recent period of warming, but such conditions would be expected frequently if the warming will continue. Thus, phenomenon of the year 2018 could be useful for understanding and prediction of the oceanographic regime reconstruction in the nearest future.
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