On the effect of a mid-ocean ridge on the sensitivity of dense water formation and marginal sea dynamics to atmospheric forcing: A conceptual model of the Nordic Seas

This study extends the existing theoretical framework for convection and dynamics in a marginal sea to the case with a mid-ocean ridge. This way, the marginal sea is characterized by both a cyclonic boundary current and a frontal current along the ridge as a result of different hydrographic properties east and west of the mid-ocean ridge, as observed in the Nordic Seas. The results from the simple conceptual model show improved agreement with high resolution idealized model simulations when including the effect of the mid-ocean ridge. We will present results from sensitivity analyses of the interior basin temperature, overflow water properties, heat loss to the atmosphere and circulation properties to changes in atmospheric forcing. The results show that the balances between the atmospheric forcing and the lateral eddy heat fluxes from the boundary current and the frontal current along the mid-ocean ridge differ between the basins east (the ‘Lofoten’ Basin) and west (the ‘Greenland’ Basin) of the mid-ocean ridge, since the eastern basin is more strongly eddy-dominated than the western basin. Therefore, when increasing the atmospheric forcing uniformly over both basins, the two basins respond differently and the temperature gradient between east and west changes. This then influences the strength of the different flow branches through the marginal sea and provides a dynamical explanation of the observed anti-correlation between the western branch (frontal current) and eastern branch (slope current) of the Norwegian Atlantic Current in the Nordic Seas. Additionally, we will present sensitivity analyses of the marginal sea properties to changes in topography to test the validity of the assumptions made in the theoretical framework.