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https://doi.org/10.5194/os-2020-71
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2020-71
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Aug 2020

14 Aug 2020

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This preprint is currently under review for the journal OS.

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

Emma L. Worthington1, Ben I. Moat2, David A. Smeed2, Jennifer V. Mecking2, Robert Marsh1, and Gerard D. McCarthy3 Emma L. Worthington et al.
  • 1University of Southampton, European Way, Southampton, SO14 3ZH, UK
  • 2National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK
  • 3ICARUS, Department of Geography, Maynooth University, Maynooth, Co. Kildare, Ireland

Abstract. A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the 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 26° N 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 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.

Emma L. Worthington et al.

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Emma L. Worthington et al.

Data sets

Atlantic meridional overturning circulation observed by the RAPID-MOCHA-WBTS array at 26N from 2004 to 2017 D. Smeed, G. McCarthy, D. Rayner, B. I. Moat, W. E. Johns, M. O. Baringer, and C. S. Meinen https://doi.org/10.5285/5acfd143-1104-7b58-e053-6c86abc0d94b

Atlantic meridional overturning circulation observed by the RAPID-MOCHA-WBTS array at 26N from 2004 to 2018 D. Smeed, B. I. Moat, D. Rayner, W. E. Johns, M. O. Baringer, D. L. Volkov, and E. Frajka-Williams https://doi.org/10.5285/8cd7e7bb-9a20-05d8-e053-6c86abc012c2

Emma L. Worthington et al.

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Short summary
The RAPID array has observed the Atlantic meridional overturning circulation (AMOC) since 2004, but the AMOC was directly calculated only five times from 1957–2004. Here we create a statistical regression model from RAPID data, relating AMOC changes to density changes within the different water masses at 26° N, and apply it to historical hydrographic data. The resulting 1981–2016 record shows that the AMOC from 2008–2012 was its weakest since the mid-1980s, but shows no overall decline.
The RAPID array has observed the Atlantic meridional overturning circulation (AMOC) since 2004,...
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