Water mass exchange between the North Atlantic and the Norwegian Sea during the past 28,000 years

Abstract

THE Greenland, Iceland and Norwegian (GIN) seas are important regulators of heat transport in the Northern Hemisphere and of ocean-atmosphere CO₂exchange^1–5. Rapid changes in the circulation of surface and deep waters in this region may induce nonlinear climatic effects and climate instabilities^2,3. Here we present carbon and oxygen isotope data that provide a record of circulation changes in the GIN seas during and at the termination of the Last Glacial Maximum (LGM). Inflow of nutrient-depleted waters from the GIN seas to form intermediate waters of the North Atlantic resulted in nutrient enrichment of North Atlantic deep water and consequent enhanced drawdown of atmospheric CO₂, contributing to the lower atmospheric $P_{\text{C}{\text{O}}_{\text{2}}}$ during the LGM. The onset of deglaciation occurred at a time of low salinity in the GIN seas and thus of reduced thermohaline circulation. Although strong thermohaline circulation was later reinitiated in the North Atlantic as deglaciation proceeded, it cannot therefore have caused the onset of warming. Similarly, we find that rapid changes in thermohaline circulation cannot account for the transient return to a cooler climate during the Younger Dryas episode.