Decadal Variability and Trends of Atlantic Water and Adjacent Water Masses Along the Continental Slope West and North of Svalbard

Abstract

In recent decades, the temperature of the West Spitsbergen Current north of Svalbard has risen substantially, with major implications for the Arctic Ocean and the Arctic sea ice cover. However, our understanding of long- term spatial and temporal variability remains limited. Using hydrography observations from the UNIS Hydrographic Database, combined with re- analysis sea ice and heat flux data, we investigate the decadal variability and trends along five climatological sections in the Svalbard Branch north of Svalbard, and analyze these observations in the context of air-ice-sea interactions. We show how the warm and saline Atlantic Water cools and freshens as it propagates along the continental slope north of Svalbard. The temperature in the upper 500 m changed on average with -0.30 ◦C per 100 km, corresponding to a vertical heat flux to the surface of up to 390 W m−2, however, with significant spatial variability between sections and temporal variability between decades. There was a reduced heat loss from the Svalbard Branch during 2000-2009, which we linked to increased surface meltwater and warmer adjacent water masses, due to a warmer and shallower Atlantic Water core, as well as changing wind patterns in this decade, pushing warm water onto the shelf. In 2010-2019, we observed a more saline surface layer with a subsequent weakened stratification, potentially caused by enhanced convective mixing, due to declining sea ice.