Seasonal to decadal variability of the subpolar gyre (D2.2)

• Main Authors: Fox, Alan, Cunningham, Stuart
• Format: Report
• Language: English
• Published: 2020
• Subjects: Arctic; Greenland; Irminger Sea; Reykjanes; Greenland-Scotland Ridge; Iceland; Labrador Sea; North Atlantic
• Online Access: https://zenodo.org/record/3631106; https://doi.org/10.5281/zenodo.3631106

Observed ocean processes, mechanisms of subpolar gyre circulation and propagation of heat anomalies Summary The aims of this Blue-Action report are to investigate the propagation of warm ocean waters from the Atlantic subpolar gyre over the Greenland-Scotland Ridge (GSR) and towards the Arctic, assess the subpolar gyre circulation in order to quantify the atmospheric and oceanic mechanisms that influence its seasonal to decadal-scale variability, and establish the link between the warm and saline eastern waters and colder and less saline western waters and the mechanisms controlling the heat and freshwater transfer from the eastern subpolar gyre to the Greenland-Scotland. The work draws primarily on data from the OSNAP (Overturning in the Subpolar North Atlantic Program) moored array and associated CTD sections, Ocean Observatories Initiative observations in the Irminger Sea, and data from Argo floats, innovative glider observations in the eastern subpolar North Atlantic, new and historical observations of flows across the Greenland-Scotland Ridge, and altimeter datasets, integrating these with model analyses. The first 21-month record from OSNAP, coupled with Argo float data, have been described as a “sea change” in our view of overturning in the subpolar North Atlantic, with the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins largely responsible for overturning and its variability in the subpolar basin. This is a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate meridional overturning circulation (MOC) variability. The observations also reveal: a highly variable MOC; the majority of the heat and freshwater transport across the OSNAP line, and its variability, is due to the variable overturning circulation rather than variations in temperature and salinity; and transports of heat northwards in the upper limb of the MOC are dominated by transports east of Reykjanes ...