The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

In this work, we describe the inter-annual variability of the Barents Sea Branch Water (BSBW), which is one of the main branches of Atlantic water that flows from the North Atlantic to the Western Arctic. We analyze an extensive data set of in situ data measurements performed from 1991 to 2023 in the northeastern part of the Barents Sea and the St. Anna Trough (SAT). This region experiences rapid climate change during the recent decades, which is expressed by sea ice decline and increasing heat inflow from the North Atlantic. Previously, the Barents Sea played the role of a buffer zone, where BSBW is effectively cooled to negative temperatures. However, significant warming was detected in the northeastern part of the Barents Sea after 2000. We demonstrate that temperature of BSBW in the northeastern part of the Barents Sea and further in SAT significantly increased during the last 20 years. In particular, BSBW with positive temperatures is regularly observed in SAT since 2008. We reveal that the increasing heat transport from the North Atlantic resulted in direct dependence of temperature of BSBW in SAT on the initial temperature of the Atlantic water at the western border of the Barents Sea. In addition, during certain years, temperature of BSBW in the study area is modified by (1) intense southwesterly winds and (2) intensity of winter convection in the Barents Sea and the resulting formation of cold dense water. Finally, we confirm the results of previous model studies, which demonstrated the shift of the cooling zone from the Barents Sea to SAT. In particular, we show that in the recent years cooling of BSBW continues in SAT by mixing with cold dense water. The observed warming of BSBW accompanied by its salinity decrease, which is observed during the last 15 years, could significantly affect thermohaline structure and circulation in the Arctic Ocean.