The Coldest and Densest Overflow Branch Into the North Atlantic is Stable in Transport, But Warming

This is the accepted version. The published version is available  on this DOI: https://doi.org/10.1029/2024GL110097

Abstract

The overflow of cold water through the Faroe Bank Channel (FBC) is the densest water crossing the Greenland-Scotland Ridge and the densest source for the Atlantic Meridional Overturning Circulation (AMOC). Here, we show that the overflow volume transport remained stable from 1996 to 2022, but that the bottom water warmed at an average rate of 0.1 °C per decade, mainly caused by warming of deep waters upstream. The salinity of the overflow water has increased as a lagged and reduced response to the salinity increase seen in the upper-layer source waters. Therefore, the potential density of the bottom water over the FBC sill shows no statistically significant trend. After entrainment of warmer ambient waters downstream of the FBC, the nonlinear density dependence upon temperature implies, however, that the overflow contributed water of reduced density to the local overturning and the deep limb of the AMOC.