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A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline

A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline
A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline
Abstract. A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the RAPID-MOCHA-WBTS (RAPID – Meridional Overturning Circulation and Heatflux Array – Western Boundary Time Series, hereafter RAPID array) with this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanographic research suggests that the AMOC may have been declining for decades or even centuries before this; however direct observations are sparse prior to 2004, giving only “snapshots” of the overturning circulation. Previous studies have used linear models based on upper-layer temperature anomalies to extend AMOC estimates back in time; however these ignore changes in the deep circulation that are beginning to emerge in the observations of AMOC decline. Here we develop a higher-fidelity empirical model of AMOC variability based on RAPID data and associated physically with changes in thickness of the persistent upper, intermediate, and deep water masses at 26N and associated transports. We applied historical hydrographic data to the empirical model to create an AMOC time series extending from 1981 to 2016. Increasing the resolution of the observed AMOC to approximately annual shows multi-annual variability in agreement with RAPID observations and shows that the downturn between 2008 and 2012 was the weakest AMOC since the mid-1980s. However, the time series shows no overall AMOC decline as indicated by other proxies and high-resolution climate models. Our results reinforce that adequately capturing changes to the deep circulation is key to detecting any anthropogenic climate-change-related AMOC decline.
1738-5261
285-299
Worthington, Emma
bfd4e9a7-3080-4bf7-b1dc-b0cc8803e97f
Moat, Ben I.
497dbb18-a98f-466b-b459-aa2c872ad2dc
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Mecking, Jennifer V
9b090069-5061-4340-b736-9690894ce203
Marsh, Robert
702c2e7e-ac19-4019-abd9-a8614ab27717
McCarthy, Gerard D.
fd87927d-feb3-447a-9cda-9558916df99f
Worthington, Emma
bfd4e9a7-3080-4bf7-b1dc-b0cc8803e97f
Moat, Ben I.
497dbb18-a98f-466b-b459-aa2c872ad2dc
Smeed, David A.
2f7e2df1-c899-4d7a-94ef-d47ddb1cc494
Mecking, Jennifer V
9b090069-5061-4340-b736-9690894ce203
Marsh, Robert
702c2e7e-ac19-4019-abd9-a8614ab27717
McCarthy, Gerard D.
fd87927d-feb3-447a-9cda-9558916df99f

Worthington, Emma, Moat, Ben I., Smeed, David A., Mecking, Jennifer V, Marsh, Robert and McCarthy, Gerard D. (2021) A 30-year reconstruction of the Atlantic meridional overturning circulation shows no decline. Ocean Science Journal, 17 (1), 285-299. (doi:10.5194/os-17-285-2021).

Record type: Article

Abstract

Abstract. A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the RAPID-MOCHA-WBTS (RAPID – Meridional Overturning Circulation and Heatflux Array – Western Boundary Time Series, hereafter RAPID array) with this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanographic research suggests that the AMOC may have been declining for decades or even centuries before this; however direct observations are sparse prior to 2004, giving only “snapshots” of the overturning circulation. Previous studies have used linear models based on upper-layer temperature anomalies to extend AMOC estimates back in time; however these ignore changes in the deep circulation that are beginning to emerge in the observations of AMOC decline. Here we develop a higher-fidelity empirical model of AMOC variability based on RAPID data and associated physically with changes in thickness of the persistent upper, intermediate, and deep water masses at 26N and associated transports. We applied historical hydrographic data to the empirical model to create an AMOC time series extending from 1981 to 2016. Increasing the resolution of the observed AMOC to approximately annual shows multi-annual variability in agreement with RAPID observations and shows that the downturn between 2008 and 2012 was the weakest AMOC since the mid-1980s. However, the time series shows no overall AMOC decline as indicated by other proxies and high-resolution climate models. Our results reinforce that adequately capturing changes to the deep circulation is key to detecting any anthropogenic climate-change-related AMOC decline.

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More information

Accepted/In Press date: 21 December 2020
Published date: 15 February 2021

Identifiers

Local EPrints ID: 447963
URI: http://eprints.soton.ac.uk/id/eprint/447963
ISSN: 1738-5261
PURE UUID: 44c1e128-130e-484e-a4d2-f7b0bce02d1a
ORCID for Emma Worthington: ORCID iD orcid.org/0000-0002-6444-6461

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Date deposited: 29 Mar 2021 16:30
Last modified: 30 Mar 2021 01:55

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Contributors

Author: Ben I. Moat
Author: David A. Smeed
Author: Jennifer V Mecking
Author: Robert Marsh
Author: Gerard D. McCarthy

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