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Response of the Atlantic overturning circulation to South Atlantic sources of buoyancy

Response of the Atlantic overturning circulation to South Atlantic sources of buoyancy
Response of the Atlantic overturning circulation to South Atlantic sources of buoyancy
The heat and salt input from the Indian to Atlantic Oceans by Agulhas Leakage is found to influence the Atlantic overturning circulation in a low-resolution Ocean General Circulation Model (OGCM). The model used is the Hamburg Large-Scale Geostrophic (LSG) model, which is forced by mixed boundary conditions. Agulhas Leakage is parameterized by sources of heat and salt in the upper South Atlantic Ocean, which extend well into the intermediate layers.

It is shown that the model's overturning circulation is sensitive to the applied sources of heat and salt. The response of the overturning strength to changes in the source amplitudes is mainly linear, interrupted once by a stepwise change. The South Atlantic buoyancy sources influence the Atlantic overturning strength by modifying the basin-scale meridional density and pressure gradients. The non-linear, stepwise response is caused by abrupt changes in the convective activity in the northern North Atlantic.

Two additional experiments illustrate the adjustment of the overturning circulation upon sudden introduction of heat and salt sources in the South Atlantic. The North Atlantic overturning circulation responds within a few years after the sources are switched on. This is the time it takes for barotropic and baroclinic Kelvin waves to reach the northern North Atlantic in this model. The advection of the anomalies takes three decades to reach the northern North Atlantic.

The model results give support to the hypothesis that the re-opening of the Agulhas Gap at the end of the last ice-age, as indicated by palaeoclimatological data, may have stimulated the coincident strengthening of the Atlantic overturning circulation.
0921-8181
293-311
Weijer, Wilbert
b7f04107-e34c-4827-ba9c-04532f535f16
de Ruijter, Wilhelmus P.M.
a433d72e-7a5a-443e-a8cb-dbfd6c2ad2a4
Sterl, Andreas
97e8969c-51b9-4b9e-8d41-f0c380e255b2
Drijfhout, Sybren S.
a5c76079-179b-490c-93fe-fc0391aacf13
Weijer, Wilbert
b7f04107-e34c-4827-ba9c-04532f535f16
de Ruijter, Wilhelmus P.M.
a433d72e-7a5a-443e-a8cb-dbfd6c2ad2a4
Sterl, Andreas
97e8969c-51b9-4b9e-8d41-f0c380e255b2
Drijfhout, Sybren S.
a5c76079-179b-490c-93fe-fc0391aacf13

Weijer, Wilbert, de Ruijter, Wilhelmus P.M., Sterl, Andreas and Drijfhout, Sybren S. (2002) Response of the Atlantic overturning circulation to South Atlantic sources of buoyancy. Global and Planetary Change, 34 (3-4), 293-311. (doi:10.1016/S0921-8181(02)00121-2).

Record type: Article

Abstract

The heat and salt input from the Indian to Atlantic Oceans by Agulhas Leakage is found to influence the Atlantic overturning circulation in a low-resolution Ocean General Circulation Model (OGCM). The model used is the Hamburg Large-Scale Geostrophic (LSG) model, which is forced by mixed boundary conditions. Agulhas Leakage is parameterized by sources of heat and salt in the upper South Atlantic Ocean, which extend well into the intermediate layers.

It is shown that the model's overturning circulation is sensitive to the applied sources of heat and salt. The response of the overturning strength to changes in the source amplitudes is mainly linear, interrupted once by a stepwise change. The South Atlantic buoyancy sources influence the Atlantic overturning strength by modifying the basin-scale meridional density and pressure gradients. The non-linear, stepwise response is caused by abrupt changes in the convective activity in the northern North Atlantic.

Two additional experiments illustrate the adjustment of the overturning circulation upon sudden introduction of heat and salt sources in the South Atlantic. The North Atlantic overturning circulation responds within a few years after the sources are switched on. This is the time it takes for barotropic and baroclinic Kelvin waves to reach the northern North Atlantic in this model. The advection of the anomalies takes three decades to reach the northern North Atlantic.

The model results give support to the hypothesis that the re-opening of the Agulhas Gap at the end of the last ice-age, as indicated by palaeoclimatological data, may have stimulated the coincident strengthening of the Atlantic overturning circulation.

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Published date: November 2002
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 349186
URI: http://eprints.soton.ac.uk/id/eprint/349186
ISSN: 0921-8181
PURE UUID: ef5ea5a7-cc91-485e-9b74-aba8b77aca29

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Date deposited: 26 Feb 2013 11:50
Last modified: 08 Jan 2022 06:00

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Contributors

Author: Wilbert Weijer
Author: Wilhelmus P.M. de Ruijter
Author: Andreas Sterl

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