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Causes of interannual-decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean

Causes of interannual-decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean
Causes of interannual-decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean
The causes and characteristics of interannual to decadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models (FLAME) and global ocean-ice models (ORCA) varying in resolution from medium- to eddy-resolving (1/2° – 1/12°), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the mid-latitude MOC variability by demonstrating that the anomalies of a (non eddy-resolving) hind-cast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and mid-latitude North Atlantic this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30–35° N, by internally-induced (eddy) fluctuations.
0894-8755
6599-6615
Biastoch, Arne
aded5e89-c706-49e6-bed2-eb41259f7b57
Böning, Claus W.
b724a76f-0dd9-440d-91ce-779f4e7501b7
Getzlaff, Julia
942892a6-174c-40c2-a0f2-9444966d8258
Molines, Jean-Marc
ff0e29c2-d4e8-4c72-995c-6e53801d823f
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Biastoch, Arne
aded5e89-c706-49e6-bed2-eb41259f7b57
Böning, Claus W.
b724a76f-0dd9-440d-91ce-779f4e7501b7
Getzlaff, Julia
942892a6-174c-40c2-a0f2-9444966d8258
Molines, Jean-Marc
ff0e29c2-d4e8-4c72-995c-6e53801d823f
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864

Biastoch, Arne, Böning, Claus W., Getzlaff, Julia, Molines, Jean-Marc and Madec, Gurvan (2008) Causes of interannual-decadal variability in the meridional overturning circulation of the mid-latitude North Atlantic Ocean. Journal of Climate, 21 (24), 6599-6615. (doi:10.1175/2008JCLI2404.1).

Record type: Article

Abstract

The causes and characteristics of interannual to decadal variability of the meridional overturning circulation (MOC) in the North Atlantic are investigated with a suite of basin-scale ocean models (FLAME) and global ocean-ice models (ORCA) varying in resolution from medium- to eddy-resolving (1/2° – 1/12°), using various forcing configurations built on bulk formulations invoking atmospheric reanalysis products. Comparison of the model hindcasts indicates similar MOC variability characteristics on time scales up to a decade; both model architectures also simulate an upward trend in MOC strength between the early 1970s and mid-1990s. The causes of the MOC changes are examined by perturbation experiments aimed selectively at the response to individual forcing components. The solutions emphasize an inherently linear character of the mid-latitude MOC variability by demonstrating that the anomalies of a (non eddy-resolving) hind-cast simulation can be understood as a superposition of decadal and longer-term signals originating from thermohaline forcing variability, and a higher-frequency wind-driven variability. The thermohaline MOC signal is linked to the variability in subarctic deep water formation, and rapidly progressing to the tropical Atlantic. However, throughout the subtropical and mid-latitude North Atlantic this signal is effectively masked by stronger MOC variability related to wind forcing and, especially north of 30–35° N, by internally-induced (eddy) fluctuations.

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Published date: December 2008

Identifiers

Local EPrints ID: 64312
URI: https://eprints.soton.ac.uk/id/eprint/64312
ISSN: 0894-8755
PURE UUID: 762fad95-9d4d-474d-8865-f4f093abc3d3

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Date deposited: 09 Dec 2008
Last modified: 13 Mar 2019 20:22

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Contributors

Author: Arne Biastoch
Author: Claus W. Böning
Author: Julia Getzlaff
Author: Jean-Marc Molines
Author: Gurvan Madec

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