Wind forcing and tides mediate transport of ocean heat from Storfjordrenna to the Arctic domain of the Barents Sea

Abstract

The Barents Sea is undergoing changes with impacts on the physical environment, e.g., the seasonal sea ice formation and extent and with large consequences for the ecosystems. There are knowledge-gaps concerning the complex pathways of Atlantic Water (AW) through the Barents Sea and the associated distribution of heat and nutrients. Records from a mooring deployed between September 2018 and November 2019 on the 70 m deep saddle between Edgeøya and Hopen islands in the Svalbard archipelago show sporadic exchange between the AW-influenced trough Storfjordrenna and the Arctic domain of the north-western Barents Sea. Forced by sea surface anomalies, the observed currents show a tendency for eastward transport across the saddle year-round. However, the eastward overflow into the Barents Sea is strongly mediated by wind forcing: The predominant north-northeasterly winds with corresponding geostrophic adjustment to Ekman transport tend to hamper and sometimes even reverse this cross-saddle current. Weaker and/or southerly winds on the other hand tend to enhance the eastward flow into the Barents Sea. The strength and shape of the overflow current vary substantially on seasonal and sub-seasonal timescales: during autumn and winter, the current is strong and barotropic, while during summer, the current is weaker and more baroclinic. On shorter time scales, the strongest oscillations occur during the ice-free autumn with a periodicity of a few days. When the area has a partial sea ice cover in winter, the strength decreases and the periodicity increases to a week or more. Further analysis of variability in temperature and current velocity shows that cross-saddle transport of positive temperature anomalies (indicating heat from waters of Atlantic origin) is evident in frequency bands associated with various drivers of mesoscale variability, such as eddies, synoptic events, and tides. There are indications that the studied area will become an increasingly important location for heat transport into the interior of the Barents Sea: A comparison between historical and recent hydrographic records show that AW is warming and shoaling in the water column in Storfjordrenna, which suggests that AW will be more easily transported across the saddle by the mentioned drivers. Furthermore, the ongoing changes in the large-scale weather patterns resulting in more southerly and southwesterly winds is hypothesized to affect the strength and persistence of the overflow on the saddle between Edgeøya and Hopen islands.