Indications and consequences of weakened Iceland-Scotland overflow

The overflow of cold water from the Arctic Mediterranean (Arctic Ocean and Nordic Seas) across the Greenland-Scotland Ridge into the Atlantic is a key process in the formation of North Atlantic Deep Water (NADW) and a driving mechanism for the Atlantic inflow to the Nordic Seas. About half the overflow flux passes east of Iceland, carried by three separate branches. Previous investigations have shown that the branch that flows through the Faroe Bank Channel decreased in flux from 1950 to 2000. We argue that the same conclusion can be drawn for the cold com ponent of the overflow across the southern part of the Iceland-Faroe Ridge and for the cold com ponent of the overflow across the Wyville-Thomson Ridge. If not compensated by unobserved increases in other sources, the results imply a reduced production of NADW and reduced inflow of Atlantic Water to the Nordic Seas. We briefly discuss the potential biological consequences of the changing transport of organisms by overflow currents, changing bottom temperature regimes in areas affected by overflow water, and changing Atlantic inflow.