The extreme winter of 2013–14: Impacts on the subpolar North Atlantic

The exceptionally low North American temperatures and the record-breaking precipitation over the British Isles during the 2013-14 winter were connected physically by anomalous ocean evaporation over the north Atlantic Subpolar Gyre region (SPG). This evaporation (or oceanic latent heat release) was also accompanied by strong sensible heat loss to the atmosphere The enhanced turbulent heat loss was caused by the surface westerly winds exiting the north American continent that were colder, drier and stronger than normal. A distinctive feature of the air-sea exchange was the extent that enhanced heat loss spanned the breath of the SPG, with evaporation anomalies intensifying in the east while sensible heat anomalies flux anomalies were stronger in the west. The immediate impact of the strong air-sea fluxes on the SPG was a reduction in ocean heat content. This is an unusual occurrence as interannual changes in SPG heat content are more typically controlled by variability in the ocean heat transport convergence. An analysis using atmospheric reanalysis, Argo profiling floats and the EN4 ocean data set indicates that an additional legacy of the winter has been the enhanced formation of a particularly dense mode of Subpolar Mode Water - one of the precursors of North Atlantic Deep Water and thus an important component of the Atlantic Meridional Overturning Circulation (AMOC). Implications for the near-future AMOC in subpolar latitudes are considered.