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Restratification Structure and Processes in the Irminger Sea
  • Miriam Frauke Sterl,
  • Marieke Femke de Jong
Miriam Frauke Sterl
NIOZ Royal Netherlands Institute for Sea Research

Corresponding Author:miriam.sterl@nioz.nl

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Marieke Femke de Jong
Royal Netherlands Institute for Sea Research NIOZ
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The Irminger Sea is one of the few regions in the ocean where deep (> 1000 m) convection occurs. Convection is followed by restratification during summer, when the stratification of the water column is reestablished and the convectively formed water is exported to the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). We investigate the interannual variability and physical drivers of restratification in the upper 600 m of the central Irminger Sea using reanalysis data for the years 1993–2019. We find that there are distinctly different restratification processes in the upper 100 m of the water column (the upper layer) and the water below it (the lower layer). In the upper layer, the stratification is dominated by a strong seasonal cycle that matches the cycle of the surface heat flux. In 2010 and 2019, there were peaks in upper layer stratification, which could be related to strong atmospheric heat and freshwater fluxes. By contrast, in the lower layer the seasonal cycle is weaker and there is strong interannual variability. Restratification can continue for up to 5 months after the surface heat flux has become negative, indicating a role for lateral advection. The strength of the restratification is strongly correlated with the eddy kinetic energy in the eastern Irminger Sea. This suggests the lateral advection is driven by warm, saline eddies from the Irminger Current. In the future, surface warming and freshening of the Irminger Sea due to anthropogenic climate change are expected to increase stratification.