Extreme oceanographic conditions in the northwestern Bering Sea in 2017-2018

Anomalous oceanographic conditions were observed in the northwestern Bering Sea in 2017-2018, including warmer air and water temperatures and reduced ice cover. Their effects on the water structure and circulation are considered. These conditions were formed on the background of warming tendency known in the Bering Sea since 2014, but the year 2018 was exceptional even relative to this background. In this year, deflections of some properties from their mean values exceeded two standard deviations (>2 sigma). The main reason for such abnormal conditions was southerly winds prevailed over the entire sea in winter because of a westward shift of the Aleutian Low; another factor was the strengthened advection of oceanic waters that still were abnormally warm after the period of extreme warming in the North-East Pacific in 2014-2016. As the result, the ice extent in winter and spring was below its mean value (more than twice lower in 2018), the air and water temperatures were above their mean values through the year (up to 15 and 3 degrees C higher, respectively, in 2018), the cold water mass was not formed at the shelf bottom in winter and was absent in summer. Under this considerable redistribution of water density, the water circulation changed, the Navarin Current weakened and was even absent in fall 2018/ and the northward water transport toward the Bering Strait was realized through the eastern shelf and delivered the coastal waters from Alaska instead of the waters from the deep-water basins, as has been usual. The oceanographic conditions in 2018 were statistical outliers, atypical even for recent period of warming, but such conditions could be expected if the warming continues. Thus, the phenomenon of 2017-2018 could be useful for understanding and predicting the reconstruction of the oceanographic regime in the near future.