Transient increase in Arctic deep-water formation and ocean circulation under sea-ice retreat

View More View Less
  • 1 Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate Research, 5007 Bergen, Norway
  • | 2 Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate Research, 5007 Bergen, Norway, Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences, University of Oslo, Norway, kerim@uib.no
  • | 3 Department of Earth Science, University of Bergen and the Bjerknes Centre for Climate Research, 5007 Bergen, Norway, mari.f.jensen@uib.no
  • | 4 Geophysical Institute, University of Bergen and the Bjerknes Centre for Climate Research, 5007 Bergen, Norway, ailin.brakstad@uib.no
  • | 5 Danish Meteorological Institute, Copenhagen, Denmark, shuting@dmi.dk
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

While a rapid sea-ice retreat in the Arctic has become ubiquitous, the potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to global warming is still under debate. As deep mixing occurs in the open-ocean close to the sea-ice edge, the strength and vertical extent of the AMOC is likely to respond to ongoing and future sea-ice retreat. Here, we investigate the link between changes in Arctic sea-ice cover and AMOC strength in a long simulation with the EC-Earth-PISM climate model under the emission scenario RCP8.5. The extended duration of the experiment (years 1850-2300) captures the disappearance of summer sea ice in 2060 and the removal of winter sea ice in 2165. By introducing a new metric, the Arctic Meridional Overturning Circulation (ArMOC), we document changes beyond the Greenland-Scotland Ridge and into the central Arctic. We find an ArMOC strengthening as the areas of deep mixing move north, following the retreating winter sea-ice edge into the Nansen Basin. At the same time, mixing in the Labrador and Greenland Seas reduces and the AMOC weakens. As the winter sea-ice edge retreats further into the regions with high surface freshwater content in the central Arctic Basin, the mixing becomes shallower and the ArMOC weakens. Our results suggest that the location of deep-water formation plays a decisive role in the structure and strength of the ArMOC; however, the intermittent strengthening of the ArMOC and convection north of the Greenland-Scotland Ridge cannot compensate for the progressive weakening of the AMOC.

Corresponding author: Anaïs Bretones, anais.bretones@uib.no

Abstract

While a rapid sea-ice retreat in the Arctic has become ubiquitous, the potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to global warming is still under debate. As deep mixing occurs in the open-ocean close to the sea-ice edge, the strength and vertical extent of the AMOC is likely to respond to ongoing and future sea-ice retreat. Here, we investigate the link between changes in Arctic sea-ice cover and AMOC strength in a long simulation with the EC-Earth-PISM climate model under the emission scenario RCP8.5. The extended duration of the experiment (years 1850-2300) captures the disappearance of summer sea ice in 2060 and the removal of winter sea ice in 2165. By introducing a new metric, the Arctic Meridional Overturning Circulation (ArMOC), we document changes beyond the Greenland-Scotland Ridge and into the central Arctic. We find an ArMOC strengthening as the areas of deep mixing move north, following the retreating winter sea-ice edge into the Nansen Basin. At the same time, mixing in the Labrador and Greenland Seas reduces and the AMOC weakens. As the winter sea-ice edge retreats further into the regions with high surface freshwater content in the central Arctic Basin, the mixing becomes shallower and the ArMOC weakens. Our results suggest that the location of deep-water formation plays a decisive role in the structure and strength of the ArMOC; however, the intermittent strengthening of the ArMOC and convection north of the Greenland-Scotland Ridge cannot compensate for the progressive weakening of the AMOC.

Corresponding author: Anaïs Bretones, anais.bretones@uib.no
Save