Formation and Circulation of Dense Water From a Two-Year Moored Record in the Northwestern Iceland Sea

The recent sea-ice retreat in the western Nordic Seas has exposed the ocean to the atmosphere in winter, thereby facilitating dense-water formation. Here, we present a 2-year long record (2016–2018) of ocean stratification and currents from the northwestern Iceland Sea, which was obtained from a mooring deployed in Eggvin Offset, an approximately 1,500 m deep passage between the Greenland and Iceland Seas. The trajectory of an Argo float deployed in winter 2017/2018 indicates a connection between Eggvin Offset and the slope north of Iceland, where the boundary currents that supply the overflows east and west of Iceland originate. However, the low transport of potential overflow water (${\sigma }_{\theta }\ge$ 27.8 kg m⁻³) through Eggvin Offset demonstrates that it is not a major passage for the exchange of dense water. Dense-water formation occurred during both winter 2016/2017 and winter 2017/2018; the mixed layer cooled and deepened mainly as an integrated response to a succession of cold-air outbreaks. Greater turbulent heat fluxes and a more even distribution of cold-air outbreaks at the mooring site in winter 2016/2017 resulted in mixed-layer depths reaching a maximum of approximately 450 m, compared to 350 m the following winter. The water formed in Eggvin Offset those recent winters attained densities similar to those of water formed in the central Iceland Sea four decades ago. This supports the notion that in a warming climate, the locus of dense-water formation has shifted from the interior basin to the western Iceland Sea.