Decreasing overflow from the Nordic seas into the Atlantic Ocean through the Faroe Bank channel since 1950

The overflow of cold, dense water from the Nordic seas, across the Greenlan d-Scotland ridge(1) and into the Atlantic Ocean is the main source for the deep water of the North Atlantic Ocean(2). This flow also helps drive the i nflow of warm, saline surface water into the Nordic seas(1). The Faroe Bank channel is the deepest path across the ridge, and the deep flow through th is channel accounts for about one-third of the total overflow(1,2). Previou s work has demonstrated that the overflow has become warmer and less saline (3,4) over time. Here we show, using direct measurements and historical hyd rographic data, that the volume flux of the Faroe Bank channel overflow has also decreased. Estimating the volume flux conservatively, we rnd a decrea se by at least 20 per cent relative to 1950. If this reduction in deep flow from the Nordic seas is not compensated by increased flow from other sourc es, it implies a weakened global thermohaline circulation and reduced inflo w of Atlantic water to the Nordic seas.