Labrador Sea subsurface density as a precursor of multidecadal variability in the North Atlantic: a multi-model study

• Main Authors: Ortega Montilla, Pablo, Robson, Jon I., Menary, Matthew, Sutton, Rowan T., Blaker, Adam, Germe, Agathe, Hirschi, Jöel J.-M., Sinha, Bablu, Hermanson, Leon, Yeager, Stephen
• Other Authors: Barcelona Supercomputing Center
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2021
• Subjects: Àrees temàtiques de la UPC::Enginyeria agroalimentària::Ciències de la terra i de la vida::Climatologia i meteorologia; Ocean circulation; Labrador Sea; Climate change; Climate change science; Multidecadal variability; North Atlantic; Labrador Sea density; Atlantic Meridional Overturning Circulation; Simulacio per ordinador
• Online Access: http://hdl.handle.net/2117/345149

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 interrelationships 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 to the strength of the subpolar AMOC and gyre circulation, and it is also linked to the subtropical AMOC, although the strength of this relationship is model-dependent and affected by the inclusion of the Ekman component. 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 to the subtropical AMOC might be more realistic. This research has been supported by the Natural Environment Research Council (grant nos. M005127/1, NE/M005097/1, NE/T013516/1, NE/T013540/1, and NE/N018044/1) and the Ministerio de Economía, Industria y Competitividad, Gobierno de España (grant no. RYC-2017-22772). Peer Reviewed Postprint (published version)