The sinking branch of the Atlantic Meridional Overturning Circulation

Sybren Drijfhout1*

* Presenting author

1) National Oceanography Centre, School of Ocean and Earth Sciences, UK

Regions with overturning feature large vertical heat transport, but little vertical mass transport. Intense downwelling in convective plumes is balanced by upwelling in surrounding areas and the area-integrated vertical mass transport in convective regions is small, because downwelling affects the vorticity by vortex stretching. In the interior the vorticity balance cannot be closed if significant downwelling occurs. Only near boundaries dissipation is large enough to balance the generation of vorticity by stretching of planetary vorticity. In a series of papers Spall and co-workers have shown that buoyancy forced downwelling is concentrated near lateral boundaries. Analysis of a NEMO025 hindcast confirms that the majority of the AMOC sinking branch indeed occurs in the boundary current along the northern half of the subpolar gyre. In the papers of Spall and others scaling relations that link the sinking to measurable, large-scale parameters have been proposed. These relations have been tested in the NEMO025 model. In this presentation I will review the recently developed sinking paradigm, how well it describes the sinking branch in an eddy-permitting model, and to what extent the sinking can be monitored from observations.

Invited talk