Mechanisms for the variability of dense water pathways in the Nordic Seas

Abstract

Interannual changes in simulated flow fields of the Nordic Seas are analyzed with respect to their dynamic causes and consequences regarding the flow of dense water from the Nordic Seas into the subpolar North Atlantic across the Greenland‐Iceland‐Scotland Ridge. The simple case of pure density‐driven outflow with closed northern boundaries shows that dense water mainly originates in the northern Lofoten Basin and flows southward in three branches, namely along the Norwegian continental slope, along the Mohn and Jan Mayen Ridges, and a weak current along the east Greenland continental slope. Adding variable exchange through Fram Strait shows a strengthening of the most western branch and strong recirculations that may reverse the other two branches. For this case, we find in‐phase modulation of the Denmark Strait overflow (DSO) by a changing Fram Strait supply and a Faroe‐Shetland transport that is in opposite phase. The scaling of this relation provides a potential explanation of recently observed DSO changes. However, details of the changes in the simulated pathways suggest, in accord with the size of the prescribed varying Fram Strait supply, basin‐wide wind stress curl and local convection, which feeds water from different source regions into the outflow pathways, as the primary cause for the upstream flow field reorganizations.