344 / 2024-09-14 16:34:51

Spatial distribution and temporal variability of the Atlantic Meridional Overturning Circulation sinking branch in the subpolar region

AMOC, sinking, variability

The sinking branch in the subpolar North Atlantic (NA) is a crucial component of the Atlantic Meridional Overturning Circulation (AMOC). Using idealized models, previous studies have shown mean-state sinking primarily occurs near continental boundaries in response to density loss. What is less explored is the spatial and temporal variability of sinking across the subpolar basin. In this study, we use ECCO data from 1992 to 2015 to investigate the locations and temporal variability of sinking across the entire subpolar region of the NA as well as the physical mechanisms driving the variability. Our results show that in the mean-state sinking mainly occurs in regions near the continental boundary of both sides of Greenland (26%), and the overflow regions (53%). Little sinking occurs in the interior of the ocean, consistent with previous studies. However, the ocean interior, especially the interior Iceland and Irminger basins, dominates the interannual variability of sinking (explained variance is 45%). This may be explained by the linear vorticity dynamics. Sinking in the boundary, on the other hand, is relatively stable throughout the time period except for the early 1990s, when enhanced sinking occurs along the western boundary of Greenland. This enhanced sinking is induced by the strengthened alongshore density loss during this time period, when enhanced convection is known to occur in the basin interior. Further work will investigate sources of the density anomalies along the boundary and their relationship with interior convection.