Seasonal variability of the Atlantic Meridional Overturning Circulation at 11° S inferred from bottom pressure measurements

Herrford, Josefine; Brandt, Peter; Kanzow, Torsten; Hummels, Rebecca; Araújo, Moacyr; Durgadoo, Jonathan V.

doi:10.5194/os-17-265-2021

Cited by 10 publications

(13 citation statements)

References 71 publications

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“…Note, when we update the MOC estimate from the pilot configuration (Meinen, Speich, Perez, et al., 2013; Meinen, Speich, Piola, et al., 2018), we also use CCMP zonal wind stress from 2009 to 2010. Nevertheless, it has been shown that at 34.5°S different wind products generate similar values for the Ekman transport (Garzoli & Baringer, 2007), while at other latitudes (e.g., 11°S, Herrford et al., 2021) the choice of the wind product might be critical.…”

Section: Methodsmentioning

confidence: 99%

“…To address this observational gap, moored arrays have been deployed at several latitudes as part of an international initiative to study the South Atlantic MOC (SAMOC; Ansorge et al., 2014; Garzoli & Matano, 2011; Herrford et al., 2021; Hummels et al., 2015; Kersalé, Meinen, et al., 2020; Kopte et al., 2017; Meinen, Speich, Perez, et al., 2013; Meinen, Speich, Piola, et al., 2018). One of the major components of this initiative is the South Atlantic MOC Basin‐wide Array (SAMBA; Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Multi‐Year Estimates of Daily Heat Transport by the Atlantic Meridional Overturning Circulation at 34.5°S

et al. 2021

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Variations in the mass and heat transported by the meridional overturning circulation (MOC) have important, well-documented, influences on global and regional climate, weather, ecosystems, and coastal sea levels. However, continuous, high-frequency, observations of these quantities have been limited to date. Multiple years of full-depth daily observations from moored instruments in the South Atlantic at 34.5°S are combined with satellite observations to resolve the volume transports in both the upper and abyssal MOC cells, and the associated full-depth meridional heat transport (MHT), on daily to interannual timescales. A newly developed method for combining satellite sea level observations with historical hydrographic measurements was used to estimate daily full-depth ocean profiles of temperature in the ocean interior where mooring coverage is sparse. The average MHT during 2013-2017 is 0.5 PW, with a daily standard deviation of 0.8 PW. The MHT variability is most strongly driven by the geostrophic relative velocity contributions (horizontal density-gradient changes). This variability is highly correlated with the volume transport variability of the MOC upper cell (r = 0.96) and modestly anti-correlated (r = −0.52) with the abyssal cell variations. An empirical relationship between the MHT and MOC values was developed allowing the reconstruction of a longer MHT time series including the pilot array period (2009)(2010). Seasonal variation of the MHT is significant, and results from strong variations of all terms (Ekman, barotropic, and baroclinic). Although the 2013-2017 shows an increasing MHT trend (0.14 PW/year), the longer time period record suggests that the apparent trend may simply be interannual modulation of MHT at 34.5°S.Plain Language Summary Changes in the meridional overturning circulation, a large system of ocean currents driven by differences in temperature and salt content as well as the winds, are known to have significant influences on the global climate system. This study presents, for the first time, full-depth, daily measurements of the volume and heat transported by this circulation system in the South Atlantic at 34.5°S based on direct observations. As the instruments anchored on the seafloor are too widely spaced in the basin interior, a new method for using satellite observations to estimate interior temperature profiles was developed and used. The roughly 4 years of continuous daily data reveal seasonal and interannual changes of these important flows. The observations also demonstrate that the volume and heat transports vary in a consistent manner with one another. This allows us to use some earlier moored observations from a pilot version of the array, extending the data record further back in time and producing ∼6 years of daily estimates of heat transport in the South Atlantic during 2009-2017, with a gap during 2010-2013. KERSALÉ ET AL.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Multi‐Year Estimates of Daily Heat Transport by the Atlantic Meridional Overturning Circulation at 34.5°S

et al. 2021

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“…The first component, T GS , has been measured by submarine telephone cables in the Florida Straits since 1982 (Baringer and Larsen, 2001;Meinen et al, 2010) (https:// www.aoml.noaa.gov/phod/floridacurrent/index.php, last access: 7 September 2020). The second component, T EK , is derived from zonal wind stress from ERA5 reanalysis products (Hersbach et al, 2020). The third component, T UMO , is the sum of the western boundary wedge transport (T WBW ), the hypsometric mass compensation (T EXT ), and the internal geostrophic transport (T INT ) over the top 1100 m. T WBW is the northward transport measured between the Abaco Island continental shelf and the WB2 mooring.…”

Section: Rapid Transport Estimates and Slamentioning

confidence: 99%

“…Other international efforts to measure the AMOC via mooring array programmes include SAMBA (South Atlantic MOC Basin-wide Array) at 34.5 • S (Meinen et al, 2018;Kersale et al, 2020), TRACOS (Tropical Atlantic Circulation and Overturning) at 11 • S (Hummels et al, 2015;Herrford et al, 2021), and OSNAP (Overturning in the Subpolar North Atlantic Program) in the subpolar North Atlantic (Lozier et al, 2019). RAPID and these other mooring array programmes have made step-change advancements in our understanding of the AMOC over the last 15 years (Frajka-Williams et al, 2019); however, they are limited to a single line of latitude and alone cannot be used to infer upstream-downstream changes in the larger-scale structure of the AMOC.…”

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confidence: 99%

A dynamically based method for estimating the Atlantic meridional overturning circulation at 26° N from satellite altimetry

et al. 2021

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Abstract. The large-scale system of ocean currents that transport warm waters in the upper 1000 m northward and return deeper cooler waters southward is known as the Atlantic meridional overturning circulation (AMOC). Variations in the AMOC have significant repercussions for the climate system; hence, there is a need for long-term monitoring of AMOC fluctuations. Currently the longest record of continuous directly measured AMOC changes is from the RAPID-MOCHA-WBTS programme, initiated in 2004. The RAPID programme and other mooring programmes have revolutionised our understanding of large-scale circulation; however, by design they are constrained to measurements at a single latitude and cannot tell us anything pre-2004. Nearly global coverage of surface ocean data from satellite altimetry has been available since the launch of the TOPEX/Poseidon satellite in 1992 and has been shown to provide reliable estimates of surface ocean transports on interannual timescales including previous studies that have investigated empirical correlations between sea surface height variability and the overturning circulation. Here we show a direct calculation of ocean circulation from satellite altimetry of the upper mid-ocean transport (UMO), the Gulf Stream transport through the Florida Straits (GS), and the AMOC using a dynamically based method that combines geostrophy with a time mean of the vertical structure of the flow from the 26∘ N RAPID moorings. The satellite-based transport captures 56 %, 49 %, and 69 % of the UMO, GS, and AMOC transport variability, respectively, from the 26∘ N RAPID array on interannual (18-month) timescales. Further investigation into the vertical structure of the horizontal transport shows that the first baroclinic mode accounts for 83 % of the interior geostrophic variability, and the combined barotropic and first baroclinic mode representation of dynamic height accounts for 98 % of the variability. Finally, the methods developed here are used to reconstruct the UMO and the AMOC for the time period pre-dating RAPID, 1993 to 2003. The effective implementation of satellite-based method for monitoring the AMOC at 26∘ N lays down the starting point for monitoring large-scale circulation at all latitudes.

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“…In recent years, observations of the BC have increased as the AMOC observing network has expanded into the South Atlantic (e.g., Ansorge et al, 2014;Frajka-Williams et al, 2019;Garzoli et al, 2012;Hummels et al, 2015;Meinen et al, 2013Meinen et al, , 2018Kersalé et al, 2020;Herrford et al, 2021). One element of this AMOC observing network, the South Atlantic MOC Basin-wide Array (SAMBA) has been under development at 34.5°S since 2009, and is presently being used to observe daily variations in the AMOC (Meinen et al, 2013(Meinen et al, , 2018Kersalé et al, 2020).…”

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confidence: 99%

Brazil Current Volume Transport Variability During 2009–2015 From a Long‐Term Moored Array at 34.5°S

et al. 2021

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Seasonal variability of the Atlantic Meridional Overturning Circulation at 11° S inferred from bottom pressure measurements

Cited by 10 publications

References 71 publications

Multi‐Year Estimates of Daily Heat Transport by the Atlantic Meridional Overturning Circulation at 34.5°S

Multi‐Year Estimates of Daily Heat Transport by the Atlantic Meridional Overturning Circulation at 34.5°S

A dynamically based method for estimating the Atlantic meridional overturning circulation at 26° N from satellite altimetry

Brazil Current Volume Transport Variability During 2009–2015 From a Long‐Term Moored Array at 34.5°S

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