Preprints
https://doi.org/10.5194/os-2021-48
https://doi.org/10.5194/os-2021-48

  01 Jun 2021

01 Jun 2021

Review status: a revised version of this preprint was accepted for the journal OS and is expected to appear here in due course.

Role of air-sea fluxes and ocean surface density on the production of deep waters in the eastern subpolar gyre of the North Atlantic

Tillys Petit1, M. Susan Lozier1, Simon A. Josey2, and Stuart A. Cunningham3 Tillys Petit et al.
  • 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 2National Oceanography Centre, Southampton, UK
  • 3Scottish Association for Marine Science, Oban, UK

Abstract. Wintertime convection in the North Atlantic Ocean is a key component of the global climate as it produces dense waters at high latitudes that flow equatorward as part of the Atlantic Meridional Overturning Circulation (AMOC). Recent work has highlighted the dominant role of the Irminger and Iceland basins in the production of North Atlantic Deep Water. Dense water formation in these basins is mainly explained by buoyancy forcing that transforms surface waters to the deep waters of the AMOC lower limb. Air-sea fluxes and the ocean surface density field are both key determinants of the buoyancy-driven transformation. We analyze these contributions to the transformation in order to better understand the connection between atmospheric forcing and the AMOC. More precisely, we study the impact of air-sea fluxes and the ocean surface density field on the transformation of subpolar mode water (SPMW) in the Iceland Basin, a water mass that “pre-conditions” dense water formation downstream. Analyses using 40 years of observations (1980–2019) reveal that the variance in SPMW transformation is mainly influenced by the variance in density at the ocean surface. This surface density is set by a combination of advection, wind-driven upwelling and surface fluxes, the latter explaining ~30 % of the variance in outcrop area as expressed by the surface area between the outcropped SPMW isopycnals. The key role of the surface density on SPMW transformation partly explains the unusually large SPMW transformation in winter 2014–2015 over the Iceland Basin.

Tillys Petit et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-48', Yavor Kostov, 14 Jul 2021
    • AC1: 'Reply on RC1', Tillys Petit, 08 Sep 2021
  • RC2: 'Comment on os-2021-48', Emma Worthington, 06 Aug 2021
    • AC2: 'Reply on RC2', Tillys Petit, 08 Sep 2021
  • RC3: 'Comment on os-2021-48', Anonymous Referee #3, 08 Aug 2021
    • AC3: 'Reply on RC3', Tillys Petit, 08 Sep 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on os-2021-48', Yavor Kostov, 14 Jul 2021
    • AC1: 'Reply on RC1', Tillys Petit, 08 Sep 2021
  • RC2: 'Comment on os-2021-48', Emma Worthington, 06 Aug 2021
    • AC2: 'Reply on RC2', Tillys Petit, 08 Sep 2021
  • RC3: 'Comment on os-2021-48', Anonymous Referee #3, 08 Aug 2021
    • AC3: 'Reply on RC3', Tillys Petit, 08 Sep 2021

Tillys Petit et al.

Tillys Petit et al.

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Short summary
From our analysis, we find that air-sea fluxes and the ocean surface density field are both key determinants of the buoyancy-driven transformation in the Iceland Basin. However, the spatial distribution of the SPMW transformation is most sensitive to surface density changes, which set the surface area for the source waters, as opposed to the direct influence of the air-sea fluxes. Hence, we highlight the importance of understanding what forces the variability of the surface density field.