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The mechanisms of the Atlantic meridional overturning circulation slowdown induced by Arctic sea ice decline

The mechanisms of the Atlantic meridional overturning circulation slowdown induced by Arctic sea ice decline
The mechanisms of the Atlantic meridional overturning circulation slowdown induced by Arctic sea ice decline

We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ;100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these buoyancy anomalies, and therefore to theAMOCslowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal winddriven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

Arctic, Climate models, Meridional overturning circulation
0894-8755
977-996
Liu, Wei
d00814ac-be1e-452d-afa2-02aa2ad97ba1
Fedorov, Alexey
c4234650-4a09-4d65-b6fc-cebd592a788f
Sévellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140
Liu, Wei
d00814ac-be1e-452d-afa2-02aa2ad97ba1
Fedorov, Alexey
c4234650-4a09-4d65-b6fc-cebd592a788f
Sévellec, Florian
01569d6c-65b0-4270-af2a-35b0a77c9140

Liu, Wei, Fedorov, Alexey and Sévellec, Florian (2019) The mechanisms of the Atlantic meridional overturning circulation slowdown induced by Arctic sea ice decline. Journal of Climate, 32 (4), 977-996. (doi:10.1175/JCLI-D-18-0231.1).

Record type: Article

Abstract

We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ;100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these buoyancy anomalies, and therefore to theAMOCslowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal winddriven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.

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More information

Accepted/In Press date: 6 November 2018
e-pub ahead of print date: 22 January 2019
Published date: 1 February 2019
Keywords: Arctic, Climate models, Meridional overturning circulation

Identifiers

Local EPrints ID: 430591
URI: http://eprints.soton.ac.uk/id/eprint/430591
ISSN: 0894-8755
PURE UUID: b2bbd327-3f2d-4520-9023-83b8912d4221

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Date deposited: 03 May 2019 16:30
Last modified: 03 Feb 2021 17:37

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Author: Wei Liu
Author: Alexey Fedorov

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