Preprints
https://doi.org/10.5194/esd-2020-83
https://doi.org/10.5194/esd-2020-83

  05 Nov 2020

05 Nov 2020

Review status: a revised version of this preprint is currently under review for the journal ESD.

Labrador Sea sub-surface density as a precursor of multi-decadal variability in the North Atlantic: a multi-model study

Pablo Ortega1,2, Jon I. Robson1, Matthew Menary3, Rowan T. Sutton1, Adam Blaker4, Agathe Germe4, Jöel J.-M. Hirschi4, Bablu Sinha4, Leon Hermanson5, and Stephen Yeager6 Pablo Ortega et al.
  • 1NCAS, University of Reading, Reading, UK
  • 2Barcelona Supercomputing Center, Barcelona, Spain
  • 3LOCEAN, Sorbonne Universités
  • 4National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK
  • 5Met Office Hadley Centre, Exeter, UK
  • 6National Center for Atmospheric Research, Boulder, USA

Abstract. The Subpolar North Atlantic (SPNA) is a region with prominent decadal variability that has experienced remarkable warming and cooling trends in the last few decades. These observed trends have been preceded by slow-paced increases and decreases in the Labrador Sea density (LSD), which are thought to be a precursor of large scale ocean circulation changes. This article analyses the inter-relationships between the LSD and the wider North Atlantic across an ensemble of coupled climate model simulations. In particular, it analyses the link between subsurface density and the deep boundary density, the Atlantic Meridional Overturning Circulation (AMOC), the Subpolar Gyre (SPG) circulation, and the upper ocean temperature in the eastern SPNA.

All simulations exhibit considerable multidecadal variability in the LSD and the ocean circulation indices, which are found to be interrelated. LSD is strongly linked with the strength of subpolar AMOC and gyre circulation, and is also linked with the subtropical AMOC, although the strength of this relationship is model dependent. The connectivity of LSD with the subtropics is found to be sensitive to different model features, including: the mean density stratification in the Labrador Sea; the strength and depth of the AMOC; and the depth at which the LSD propagates southward along the western boundary. Several of these quantities can also be computed from observations, and comparison with these observation-based quantities suggests that models representing a weaker link with the subtropical AMOC may be more realistic. This would imply that RAPID AMOC measurements might not be adequate to represent decadal to multidecadal changes in the subpolar overturning circulation.

Pablo Ortega et al.

 
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Pablo Ortega et al.

Pablo Ortega et al.

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Short summary
Deep Labrador Sea densities are receiving increasing attention because of their link with many of the processes that govern decadal climate oscillations in the North Atlantic, and their potential use as a precursor of those changes. This article explores those links and how they are represented in global climate models, documenting the main differences across models. Models are finally compared with observational products to identify the ones that reproduce the links more realistically.
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