Impact on the ocean of extreme Greenland Sea heat loss in the HadCM3 coupled ocean‐atmosphere model

Abstract

The ocean response to air‐sea flux variability in the Greenland Sea is investigated using a 1000 year run of the coupled ocean‐atmosphere model HadCM3. Evaluation of the density flux reveals that net heat flux anomalies have a greater impact on surface density changes than anomalies in both net evaporation and ice melt/formation. Averaged over the Greenland Sea, the annual mean density flux due to heat loss is 1.8 × 10−6 kg m−2 s−1, an order of magnitude greater than the net evaporation and the ice melt and formation terms, which are −0.1 and −0.2 × 10−6 kg m−2 s−1, respectively. Extreme winter heat loss events reach 250 W m−2 and are associated with reduced ice cover and anomalously strong northerly airflow over the Greenland Sea. They result in enhanced convection and modify the properties of deep water flowing south through the Denmark Strait. The deep water transport increases by about 30% when the strongest and weakest heat loss events are compared, and there is a corresponding reduction in temperature and salinity by up to 2.3°C and 0.38 psu. We also find significant correlations between deep western basin temperatures at 60°, 55°, and 49°N and the Greenland Sea heat flux anomalies which peak at lags of up to 4 years with the time delay increasing toward more southerly latitudes. Our results suggest that Greenland Sea heat flux variability is a key variable for understanding recent observations of significant interannual variability in Denmark Strait transport characteristics.