1. Faroese Fisheries Laboratory, PO Box 3051, FO-110 Tórshavn, Faroe Islands
2. FRS Marine Laboratory, PO Box 101, Aberdeen AB11 9DB, UK
3. Bjerknes Centre for Climate Research and Geophysical Institute, N-5024 Bergen, Norway

Correspondence to: Bogi Hansen¹ Correspondence and requests for material should be addressed to B.H. (e-mail: Email: bogihan@frs.fo).

Abstract

The overflow of cold, dense water from the Nordic seas, across the Greenland–Scotland ridge¹ and into the Atlantic Ocean is the main source for the deep water of the North Atlantic Ocean². This flow also helps drive the inflow of warm, saline surface water into the Nordic seas¹. The Faroe Bank channel is the deepest path across the ridge, and the deep flow through this channel accounts for about one-third of the total overflow^{1, 2}. Previous work has demonstrated that the overflow has become warmer and less saline^{3, 4} over time. Here we show, using direct measurements and historical hydrographic data, that the volume flux of the Faroe Bank channel overflow has also decreased. Estimating the volume flux conservatively, we find a decrease 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 sources, it implies a weakened global thermohaline circulation and reduced inflow of Atlantic water to the Nordic seas.