Subpolar North Atlantic overturning and gyre-scale circulation in the summers of 2014 and 2016

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Holliday, N. P., Bacon, S., Cunningham, S. A., Gary, S. F., Karstensen, J., King, B. A., Li, F., McDonagh, E. L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Canada; Greenland; Iceland; Labrador Sea; North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/520247/; https://nora.nerc.ac.uk/id/eprint/520247/1/Holliday_final_25May18_withFigs_low%20%28002%29.pdf; https://nora.nerc.ac.uk/id/eprint/520247/7/Holliday_et_al-2018-Journal_of_Geophysical_Research__Oceans.pdf; https://doi.org/10.1029/2018JC013841

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system through its transport of heat and freshwater. The subpolar North Atlantic (SPNA) is a region where the AMOC is actively developed and shaped though mixing and water mass transformation, and where large amounts of heat are released to the atmosphere. Two hydrographic trans-basin sections in the summers of 2014 and 2016 provide highly spatially resolved views of the SPNA velocity and property fields on a line from Canada to Greenland to Scotland. Estimates of the AMOC, isopycnal (gyre-scale) transport, and heat and freshwater transport are derived from the observations. The overturning circulation, the maximum in northward transport integrated from the surface to seafloor and computed in density space, has a high range, with 20.6 ± 4.7 Sv in June-July 2014 and 10.6 ± 4.3 Sv in May-August 2016. In contrast the isopycnal (gyre-scale) circulation was lowest in summer 2014: 41.3 ± 8.2 Sv compared to 58.6 ± 7.4 Sv in 2016. The heat transport (0.39 ± 0.08 PW in summer 2014, positive is northwards) was highest for the section with the highest AMOC, and the freshwater transport was largest in summer 2016 when the isopycnal circulation was high (-0.25 ± 0.08 Sv). Up to 65% of the heat and freshwater transport was carried by the isopycnal circulation, with isopycnal property transport highest in the western Labrador Sea and the eastern basins (Iceland Basin to Scotland).