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Review
. 2023 Dec 11;381(2262):20220195.
doi: 10.1098/rsta.2022.0195. Epub 2023 Oct 23.

Should AMOC observations continue: how and why?

E Frajka-Williams  1   2 , N Foukal  3 , G Danabasoglu  4
Affiliations
Review

Should AMOC observations continue: how and why?

E Frajka-Williams et al. Philos Trans A Math Phys Eng Sci. .

Abstract

The Atlantic meridional overturning circulation (AMOC) is a large-scale circulation pattern responsible for northward heat transport in the Atlantic and is associated with climate variations on a wide range of time scales. Observing the time-varying AMOC has fundamentally changed our understanding of the large-scale ocean circulation and its interaction with the climate system, as well as identified shortcomings in numerical simulations. With a wide range of gains already achieved, some now ask whether AMOC observations should continue. A measured approach is required for a future observing system that addresses identified gaps in understanding, accounts for shortcomings in observing methods and maximizes the potential to guide improvements in ocean and climate models. Here, we outline a perspective on future AMOC observing and steps that the community should consider to move forward. This article is part of a discussion meeting issue 'Atlantic overturning: new observations and challenges'.

Keywords: AMOC; ocean observations; overturning.

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Conflict of interest statement

We declare we have no competing interests.

Figures

Figure 1.
Figure 1.
The Atlantic meridional overturning circulation (AMOC) viewed as a slice through the Atlantic from south to north [1]. Northward flowing intermediate water is found in the top 1000 m, and southward flowing water between 1000–4000 m. In the South Atlantic, there is also significant northward flowing water below 3000 m originating around Antarctica.
Figure 2.
Figure 2.
Monthly values of AMOC transport from four observing arrays, updated from [8]: OSNAP (green), RAPID 26∘N (red), MOVE 16∘N (magenta) and SAMBA 34.5∘S (blue/grey). For SAMBA, two estimates are shown where the blue values are from [31] and the grey values from [32].
Figure 3.
Figure 3.
Flowchart schematic showing the measurements, calculations and choices that are made to estimate the AMOC at 26∘N. Blue parallelograms are measured variables (e.g. temperature T, conductivity C, pressure P, velocity V and also including reanalysis winds); white circles are derived quantities (e.g. salinity S, density ρ, dynamic height Φ(z), velocity profiles V(z) and absolute geostrophic velocities vg(z)). Calculations are in grey (e.g. interpolating discrete measurements onto a regularly spaced vertical profile, calculating geostrophic shear between profiles of dynamic height, or extrapolating from moorings to the continental slope), while methodological choices are in red diamonds (e.g. the choice of filling data in the near-surface layer, choice of latitude for f, how to fill bottom triangles, and calculating the reference level velocity vref). The component transports in units of transport-per-unit-depth (m2 s−1 or Sv m−1) are in red rectangles (mid-ocean calculated from dynamic height, boundary currents from direct velocity measurements and surface Ekman transport), while the AMOC transports (streamfunction Ψ(z) and maximum MOC) are in ovals. The arrows show the flow of information. Measured quantities may have measurement errors associated with them, while methodological choices can introduce differences between AMOC array estimates.
Figure 4.
Figure 4.
Diagram of a section across the Atlantic showing where (geographically) measurement and methodological uncertainties enter into AMOC calculations. Moorings are shown in blue dashed lines, where boundary moorings measuring velocity are at the left/western edge while the other moorings have CTD measurements. The methodological choices of what to do about unmeasured regions are in red shading including the surface (top ∼50 m above the tops of sub-surface moorings), the bottom triangles between deep moorings and the continental slope, the abyssal transports (in the case of 26∘N, this is the Antarctic Bottom Water (AABW)) and the continental shelf (in red hatching). The choice of a reference level velocity is indicated here as vref or the reference level velocity. For RAPID, this is using a deep level (4820 dbar), but it could be at an intermediate depth (in the case of SAMBA 34.5∘S) or at the sea surface (as for OSNAP).
Figure 5.
Figure 5.
An iterative process for designing an ocean observing system.
See this image and copyright information in PMC

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  • Atlantic overturning: new observations and challenges.
    Srokosz MA, Holliday NP, Bryden HL. Srokosz MA, et al. Philos Trans A Math Phys Eng Sci. 2023 Dec 11;381(2262):20220196. doi: 10.1098/rsta.2022.0196. Epub 2023 Oct 23. Philos Trans A Math Phys Eng Sci. 2023. PMID: 37866387 Free PMC article.

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