Transformation of Atlantic Water in the Barents Sea between 1948 and 2002

Water of Atlantic origin forms a layer of several hundred meter thickness (between 200m and 1000m depth) in the Arctic Ocean. After a passage of up to several decades along cyclonic loops in the Arctic Ocean basins it leaves the Arctic via Fram Strait to be one of the source waters of the meridional overturning circulation. The hydrographic characteristics, pathways and distribution of the Arctic Ocean's Atlantic Water layer have experienced significant changes in the last decades due to variations of local and remote atmospheric conditions.

Two branches of Atlantic Water feed this mid-depth Atlantic Water layer: one enters via Fram Strait, the other one crosses the Barents Sea and northern Kara Sea. During this passage the latter branch is subject to mixing processes with coastal and Polar watermasses, strong winter heat-loss, ice formation and melt and shifts of pathways on the shelf. The intensity of these processes are variable on seasonal to decadal timescale and add to the variability which has been imposed on the advected Atlantic Water in the Nordic Sea. We discuss the conditions for the formation of dense water on the Barents Sea and northern Kara Sea shelves during the last five decades. For this purpose we analyze a hindcast performed with a coupled ice-ocean model and compare it with observations.

The light shelf water components feed the upper ocean and the halocline of the Arctic Ocean with strong input of melt water and coastal runoff. The densest water formed on the shelves enters the central Arctic via the deep St. Anna Trough. Its density, which determines its final position in the water column of the Arctic basins, is variable on interannual to pentadal timescale. Our analysis shows periods of an anomalously light dense water in the early 1960s, the mid 1970s and the mid 1990s. We will discuss in what way the Atlantis Water transformation on the shelves is influenced by the local fluxes of salt, heat and momentum and the upstream conditions in the Nordic Seas. We will also pin down its dependence on the large scale sea level pressure patterns. The investigation is part of the Arctic Ocean Model Intercomparison Program.