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Isopycnal eddy stirring dominates thermohaline mixing in the upper subpolar North Atlantic
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  • Bieito Fernández Castro,
  • Daniel Fernandez Roman,
  • Bruno Ferron,
  • Marcos Fontela,
  • Pascale Lherminier,
  • Alberto C. Naveira Garabato,
  • Fiz Pérez,
  • Carl Pranas Spingys,
  • Kurt Polzin,
  • Anton Velo
Bieito Fernández Castro
University of Southampton

Corresponding Author:[email protected]

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Daniel Fernandez Roman
Universidade de Vigo
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Bruno Ferron
French National Centre for Scientific Research (CNRS)
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Marcos Fontela
Instituto de Investigacións Mariñas, IIM-CSIC
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Pascale Lherminier
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Alberto C. Naveira Garabato
University of Southampton
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Fiz Pérez
Instituto de Investigaciones Marinas. IIM-CSIC
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Carl Pranas Spingys
National Oceanography Centre
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Kurt Polzin
Woods Hole Oceanographic Institution
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Anton Velo
Instituto de Investigaciones Marinas. IIM-CSIC
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The Atlantic Meridional Overturning Circulation (AMOC) entails vigorous thermohaline transformations in the subpolar North Atlantic (SPNA). There, warm and saline waters originating in the subtropics are converted into cooler and fresher waters by a combination of surface fluxes and sub-surface thermohaline mixing. Using microstructure measurements and a small-scale variance conservation framework, we quantify the diapycnal and isopycnal contributions to thermohaline mixing within the eastern SPNA. Isopycnal stirring is found to account for 65% of thermal and 84% of haline variance dissipation in the upper 400 m of the eastern SPNA, suggesting an important role of isopycnal stirring in regional water-mass transformations. By applying the tracer variance method to two tracers, we underscore the special significance of isopycnal stirring for tracers weakly coupled to density, such as biologically-active tracers. Our findings thus highlight the central role of isopycnal stirring in both the AMOC and biogeochemical dynamics within the SPNA.
07 Dec 2023Submitted to ESS Open Archive
07 Dec 2023Published in ESS Open Archive