EGU General Assembly 2020
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Dynamical constraints on the choice of the North Atlantic subpolar gyre index

Vimal Koul1,2, Jan-Erk Tesdal3, Manfred Bersch1, Sebastian Brune1, Hjálmar Hátún4, Helmuth Haak5, Leonard Borchert6, Corinna Schrum2,1, and Johanna Baehr1
Vimal Koul et al.
  • 1Universität Hamburg, Institute of Oceanography, Center for Earth System Research and Sustainability, Hamburg, Germany (
  • 2Helmholtz Zentrum Geesthacht, Institute of Coastal Research, Germany
  • 3Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York
  • 4Faroe Marine Research Institute, Faroe Islands
  • 5Max Planck Institute for Meteorology, Hamburg, Germany
  • 6Universités Sorbonne (SU/CNRS/IRD/MNHN), LOCEAN Laboratory, Institut Pierre Simon Laplace (IPSL), Paris, France

The North Atlantic Subpolar Gyre (SPG) has been widely implicated as the source of large-scale changes in the subpolar marine environment. However, inconsistencies between different indices of SPG strength based on Sea Surface Height (SSH) observations have raised questions about the active role SPG strength and size play in determining water properties in the eastern subpolar North Atlantic (ENA). Here, by analyzing SSH-based and various other SPG-strength indices derived from observations and a global coupled model, we show that the interpretation of SPG strength-salinity relationship is dictated by the choice of the SPG index. Our results emphasize that SPG indices should be interpreted cautiously because they represent variability in different regions of the subpolar North Atlantic. Idealized Lagrangian trajectory experiments illustrate that zonal shifts of main current pathways in the ENA and meridional shifts of the North Atlantic Current (NAC) in the western intergyre region during strong and weak SPG circulation regimes are manifestations of variability in the size and strength of the SPG. Such shifts in advective pathways modulate the proportions of subpolar and subtropical water reaching the ENA, and thus impact salinity. Inconsistency among SPG indices arises due to the inability of some indices to capture the meridional shifts of the NAC in the western intergyre region. Overall, our results imply that salinity variability in the ENA is not exclusively sourced from the subtropics, instead the establishment of a dominant subpolar pathway also points to redistribution within the SPG.

How to cite: Koul, V., Tesdal, J.-E., Bersch, M., Brune, S., Hátún, H., Haak, H., Borchert, L., Schrum, C., and Baehr, J.: Dynamical constraints on the choice of the North Atlantic subpolar gyre index, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2645,, 2020.


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