Tracing the sinking of dense ocean waters
In this study, we investigate the sinking of dense water masses in the North Atlantic. Therefore, we use data from an eddy permitting (0.1 degree) ocean model of the Parallel Ocean Program (POP). Velocity fields of the model are used to advect Lagrangian floats with the Connectivity Modelling System (CMS). Model and float data are used to identify regions where water masses sink into the deep ocean. Theoretical considerations predict that water masses can only sink if the geostrophic balance is broken. We identify mechanisms that are responsible for the ageostrophic dynamics and compare our findings with frequently discussed theories. Especially, we focus on the vertical vorticity balance of the boundary currents.
Since eddies seem to play a dominant role for the deep water sinking, it is questionable to which extent coarser resolved ocean models that do not resolve the eddies are able to capture the deep water sinking. Especially, we aim to clarify if the sinking in a coarser resolved counterpart of the POP ocean model (1 degree) is due to different mechanisms compared to its eddy permitting (0.1 degree) counterpart. By this, we aim at understanding how the deep sinking of water masses as one part of the Meridional Overturning Circulation is represented in typically coarser resolved climate models and how realistic these processes are represented in comparison to higher resolved ocean models.