A 70-year perspective on water-mass transformation in the Greenland Sea: from thermobaric to thermal convection

The Greenland Sea is known as one of only few locations globally where bottom-reaching convection used to take place. Over the past 70 years, the hydrography and stratification in the Greenland Sea changed substantially. As a consequence, the production of Greenland Sea Deep Water stopped, and a less dense water mass started to form. While Greenland Sea Deep Water was too dense to flow across the Greenland-Scotland Ridge and therefore remained in the deep Nordic Seas, the new water mass contributes to the AMOC. The transition from production of Greenland Sea Deep Water to less dense intermediate water was caused by a freshening event in the 1980s with subsequent warming. In the more recent decades, the Greenland Sea transitioned from a salinity- to a temperature-stratified ocean. This changed the seasonal cycle of convection and has important implications for other regions that are currently undergoing a similar development, such as the Arctic Ocean and the Barents Sea. We analyze the development of the hydrography in the Greenland Sea in concert with the changes in the sea-ice cover and surface heat fluxes. From that, we identify variability in the Atlantic-origin Water properties as the main driver of the long-term development of stratification in the Greenland Sea.