Greenland and Labrador Sea convection in an ocean-sea ice simulation 1948–2002

Deep convective mixing in the northern North Atlantic is regarded as globally important due to the impact on the large scale meridional overturning circulation in the ocean. Results from hindcast simulations with a high-resolution ocean-sea ice model of the Arctic and subpolar North Atlantic covering the NCEP reanalysis period contain strong interannual variability of convective mixing in the Greenland and Labrador seas. The model reproduces observed deep convection in the Greenland Sea during the 1960s and 1970s and its cessation in the 1980s. Deep convective mixing in the Labrador Sea takes over in the 1980s and 1990s. Composites for ocean, sea ice, and atmosphere conditions for strong (weak) convective activity at both centers are compared. We confirm the proposed NAO related seesaw between Greenland and Labrador Sea convection until the end of the 1990s. While the Labrador Sea convection is mostly related to the large scale atmospheric conditions, convection in the Greenland Sea depends much more on the local sea ice formation, transport, and melting. This is the reason for the breakdown of the anticorrelation with the NAO in a weak recurrence of convective activity in the Greenland Sea in the 1990s.