Southern Ocean deep convection in global climate models: A driver for variability of subpolar gyres and Drake Passage transport on decadal time scales

Behrens, Erik, Rickard, Graham, Morgenstern, Olaf, Martin, Torge, Osprey, Annette and Joshi, Manoj ORCID: https://orcid.org/0000-0002-2948-2811 (2016) Southern Ocean deep convection in global climate models: A driver for variability of subpolar gyres and Drake Passage transport on decadal time scales. Journal of Geophysical Research C: Oceans, 121 (6). pp. 3905-3925.

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Abstract

We investigate the individual and joint decadal variability of Southern Ocean state quantities, such as the strength of the Ross and Weddell Gyres, Drake Passage transport, and sea ice area, using the National Institute of Water and Atmospheric Research UK Chemistry and Aerosols (NIWA-UKCA) model and CMIP5 models. Variability in these quantities is stimulated by strong deep reaching convective events in the Southern Ocean, which produce an Antarctic Bottom Water-like water mass and affect the large-scale meridional density structure in the Southern Ocean. An increase in the (near) surface stratification, due to freshwater forcing, can be a precondition for subsequent strong convection activity. The combination of enhanced-gyre driven sea ice and freshwater export, as well as ongoing subsurface heat accumulation, lead to a time lag between changes in oceanic freshwater and heat content. This causes an ongoing weakening of the stratification until sudden strong mixing events emerge and the heat is released to the atmosphere. We find that strong convection reduces sea ice cover, weakens the subpolar gyres, increases the meridional density gradient and subsequently results in a positive Drake Passage transport anomaly. Results of available CMIP5 models confirm that variability in sea ice, Drake Passage transport, and the Weddell Gyre strength is enhanced if models show strong open ocean convective events. Consistent relationships between convection, sea ice, Drake Passage transport, and Ross Gyre strength variability are evident in most models, whether or not they host open ocean convection.

Item Type:	Article
Additional Information:	Copyright 2016. American Geophysical Union. All Rights Reserved.
Uncontrolled Keywords:	southern ocean,decadal variability,cmip5,model bias,open ocean convection,sdg 13 - climate action ,/dk/atira/pure/sustainabledevelopmentgoals/climate_action
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	University of East Anglia Schools > Faculty of Science > Tyndall Centre for Climate Change Research Faculty of Science > Research Centres > Tyndall Centre for Climate Change Research Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences Faculty of Science > Research Groups > Climatic Research Unit
Depositing User:	Pure Connector
Date Deposited:	13 May 2016 15:01
Last Modified:	20 Oct 2023 01:03
URI:	https://ueaeprints.uea.ac.uk/id/eprint/58737
DOI:	10.1002/2015JC011286

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