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Pending recovery in the strength of the meridional overturning circulation at 26° N

Pending recovery in the strength of the meridional overturning circulation at 26° N
Pending recovery in the strength of the meridional overturning circulation at 26° N
The strength of the Atlantic meridional overturning circulation (AMOC) at 26∘ N has now been continuously measured by the RAPID array over the period April 2004–September 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transport from hydrographic sections. The continuous measurements have unveiled striking variability on timescales of days to a decade, driven largely by wind forcing, contrasting with previous expectations about a slowly varying buoyancy-forced large-scale ocean circulation. However, these measurements were primarily observed during a warm state of the Atlantic multidecadal variability (AMV) which has been steadily declining since a peak in 2008–2010. In 2013–2015, a period of strong buoyancy forcing by the atmosphere drove intense water-mass transformation in the subpolar North Atlantic and provides a unique opportunity to investigate the response of the large-scale ocean circulation to buoyancy forcing. Modelling studies suggest that the AMOC in the subtropics responds to such events with an increase in overturning transport, after a lag of 3–9 years. At 45∘ N, observations suggest that the AMOC may already be increasing. Examining 26∘ N, we find that the AMOC is no longer weakening, though the recent transport is not above the long-term mean. Extending the record backwards in time at 26∘ N with ocean reanalysis from GloSea5, the transport fluctuations at 26∘ N are consistent with a 0- to 2-year lag from those at 45∘ N, albeit with lower magnitude. Given the short span of time and anticipated delays in the signal from the subpolar to subtropical gyres, it is not yet possible to determine whether the subtropical AMOC strength is recovering nor how the AMOC at 26∘ N responds to intense buoyancy forcing.
1812-0792
863-874
Moat, Ben I.
497dbb18-a98f-466b-b459-aa2c872ad2dc
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Frajka-williams, Eleanor
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
Desbruyères, Damien G.
64e32ac3-c255-40e4-ac71-55d4749d3d43
Beaulieu, Claudie
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Johns, William E.
e09ba73d-f275-4ff3-a07c-dfb8f1622b21
Rayner, Darren
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Sanchez-franks, Alejandra
ce8ef4a4-086a-4402-a2c1-72db55ff811f
Baringer, Molly O.
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Volkov, Denis
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Jackson, Laura C.
c610e2ea-b151-4317-b44b-f4ac7a7e2070
Bryden, Harry L.
7f823946-34e8-48a3-8bd4-a72d2d749184
Moat, Ben I.
497dbb18-a98f-466b-b459-aa2c872ad2dc
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Frajka-williams, Eleanor
da86044e-0f68-4cc9-8f60-7fdbc4dc19cb
Desbruyères, Damien G.
64e32ac3-c255-40e4-ac71-55d4749d3d43
Beaulieu, Claudie
28d711f1-59db-48d5-bd5c-eb04ae055dbc
Johns, William E.
e09ba73d-f275-4ff3-a07c-dfb8f1622b21
Rayner, Darren
60eaf35c-c54e-447b-8551-efc08637d122
Sanchez-franks, Alejandra
ce8ef4a4-086a-4402-a2c1-72db55ff811f
Baringer, Molly O.
05e0f722-83ee-4dc2-ac6e-2505c8b29f31
Volkov, Denis
2aed7090-5b05-4633-9948-4d9303aebe75
Jackson, Laura C.
c610e2ea-b151-4317-b44b-f4ac7a7e2070
Bryden, Harry L.
7f823946-34e8-48a3-8bd4-a72d2d749184

Moat, Ben I., Smeed, David A., Frajka-williams, Eleanor, Desbruyères, Damien G., Beaulieu, Claudie, Johns, William E., Rayner, Darren, Sanchez-franks, Alejandra, Baringer, Molly O., Volkov, Denis, Jackson, Laura C. and Bryden, Harry L. (2020) Pending recovery in the strength of the meridional overturning circulation at 26° N. Ocean Science, 16 (4), 863-874, [51]. (doi:10.5194/os-16-863-2020).

Record type: Article

Abstract

The strength of the Atlantic meridional overturning circulation (AMOC) at 26∘ N has now been continuously measured by the RAPID array over the period April 2004–September 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transport from hydrographic sections. The continuous measurements have unveiled striking variability on timescales of days to a decade, driven largely by wind forcing, contrasting with previous expectations about a slowly varying buoyancy-forced large-scale ocean circulation. However, these measurements were primarily observed during a warm state of the Atlantic multidecadal variability (AMV) which has been steadily declining since a peak in 2008–2010. In 2013–2015, a period of strong buoyancy forcing by the atmosphere drove intense water-mass transformation in the subpolar North Atlantic and provides a unique opportunity to investigate the response of the large-scale ocean circulation to buoyancy forcing. Modelling studies suggest that the AMOC in the subtropics responds to such events with an increase in overturning transport, after a lag of 3–9 years. At 45∘ N, observations suggest that the AMOC may already be increasing. Examining 26∘ N, we find that the AMOC is no longer weakening, though the recent transport is not above the long-term mean. Extending the record backwards in time at 26∘ N with ocean reanalysis from GloSea5, the transport fluctuations at 26∘ N are consistent with a 0- to 2-year lag from those at 45∘ N, albeit with lower magnitude. Given the short span of time and anticipated delays in the signal from the subpolar to subtropical gyres, it is not yet possible to determine whether the subtropical AMOC strength is recovering nor how the AMOC at 26∘ N responds to intense buoyancy forcing.

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Published date: 23 July 2020

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Local EPrints ID: 442710
URI: http://eprints.soton.ac.uk/id/eprint/442710
ISSN: 1812-0792
PURE UUID: 41aa9b88-6b00-47c3-93c9-695251454f0d
ORCID for Eleanor Frajka-williams: ORCID iD orcid.org/0000-0001-8773-7838
ORCID for Harry L. Bryden: ORCID iD orcid.org/0000-0002-8216-6359

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Date deposited: 23 Jul 2020 16:32
Last modified: 18 Feb 2021 17:14

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Contributors

Author: Ben I. Moat
Author: David A. Smeed
Author: Eleanor Frajka-williams ORCID iD
Author: Damien G. Desbruyères
Author: Claudie Beaulieu
Author: William E. Johns
Author: Darren Rayner
Author: Alejandra Sanchez-franks
Author: Molly O. Baringer
Author: Denis Volkov
Author: Laura C. Jackson
Author: Harry L. Bryden ORCID iD

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