Decadal Variability of Transports through Barents Sea Opening: Changing impact of Large-Scale Wind Forcing

The Barents Sea Opening (BSO) is one of two Atlantic gateways connecting the North Atlantic Ocean to the Arctic Ocean. The ocean transport through the BSO is composed of warm and saline Atlantic Water inflow in the central and southern parts of the section and cold Polar and modified Atlantic Water outflow in the north. The variability of strengths of both inflow and outflow largely controls the evolution of the net ocean heat transport into the Barents Sea, locally impacting e.g., ocean-atmosphere heat fluxes, sea ice extent, and deep-water formation. Moreover, changes in heat fluxes and sea ice extent have been shown to impact remote properties such as wintertime weather in northern Europe and water properties in the central Arctic Ocean.

In this study, we identified and disentangled the contributions of local and remote atmospheric forcing mechanisms of the wintertime volume transport through BSO from 1970-2020. In order to understand the variability and co-variability of the local and remote forcing mechanisms and the linked transport anomalies, we performed dedicated model experiments with the unstructured ocean and sea ice model FESOM2. In addition to a hindcast control simulation using JRA55 reanalysis forcing, we performed two additional model experiments in which we combined JRA55 forcing with CORE1 normal year forcing in a way that the simulations are forced with JRA55 (CORE1) in the Arctic domain and CORE1 (JRA55) outside the Arctic domain. This setup allows the separation of local and upstream forced transport variability. Our experiments show, that both BSO inflow and outflow exhibit strong variability on interannual to decadal timescales. While inflow variability is forced to a similar degree by local alongshore winds and alongshore winds upstream in the Norwegian Sea, the outflow variability is almost entirely forced by wind stress curl anomalies over the northern Barents Sea shelf. Moreover, the inflow anomalies forced upstream are highly correlated with the North Atlantic Oscillation (NAO) while the transport anomalies forced locally exclusively correlate with the NAO during periods of a negative NAO. Furthermore, we observe a drastic drop in the correlation of inflow anomalies forced upstream and the NAO around the year 2000 - the same period in which winters with strongly enhanced outflow anomalies (97/98, 03/04) are found. By expanding our analysis to cyclone activity in the northern North Atlantic, we link the loss of co-variability of NAO and BSO inflow to an anomalous southward deflection of cyclones in these winters, affecting the alongshore winds in the Norwegian Sea as well as the wind stress curl over the northern Barents Sea shelf.

In general, this study aims to improve our understanding of the drivers of volume and heat transport variability in the BSO as a key factor for (sub-)Arctic, ocean, weather, and climate variability.