Increased presence of Atlantic Water on the shelf south-west of Spitsbergen with implications for the Arctic fjord Hornsund

Abstract

Atlantic Water is a major contributor to the largest zonal variability in ocean properties and air-sea-ice interaction in the Nordic Seas and the European Arctic. Climate change has amplified warming and intensified extreme events, in both the ocean and the atmosphere, with severe implications for the marine environment. Here, we present our long-term (1999–2020) hydrographic observations from the shelf south-west of Spitsbergen, focusing on the extent of Atlantic and Arctic waters, and we examine their impact on the water masses in Hornsund fjord. Our results show an 8% y−1 increase of the Atlantic Water volume fraction on the shelf during the period 1999–2020, especially noticeable in the last decade. Although this does not imply a significant increase in the amount of waters of the Atlantic origin in the fjord, the greater role of Atlantic Water is attributed to changes in water properties (volume and temperature) of the upper water layer in Hornsund. The strong controlling effect of Arctic Water, transported by the Spitsbergen Polar Current, on the salinity of the fjord surface and intermediate layers is helping to preserve the Arctic character of Hornsund. Nevertheless, ongoing Atlantification of the Nordic and Barents Seas may reduce supply of Arctic Water, thereby diminishing the role of the Spitsbergen Polar Current as the agent mitigating the impact of Atlantic Water on the west Spitsbergen fjords. In the future, this may contribute to the disappearance of the gradation in hydrographic conditions currently observed in the fjords along the west coast of Spitsbergen.