Highly variable upper and abyssal overturning cells in the South Atlantic

Kersalé, Marion; Meinen, Christopher S.; Perez, Renellys C.; Hénaff, Matthieu Le; Valla, Daniel; Lamont, Tarron; Sato, O. T.; Dong, Shenfu; Terre, T.; Caspel, Mathias van; Chidichimo, María Paz; Berg, Marcel van den; Speich, Sabrina; Piola, Alberto R.; Campos, Edmo; Ansorge, Isabelle; Volkov, Denis; Lumpkin, Rick; Garzoli, Silvia L.

doi:10.1126/sciadv.aba7573

Cited by 34 publications

(107 citation statements)

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“…At interannual time scales, large (∼3 Sv) changes in the AMOC max have been observed both at 26.5°N and 34.5°S (e.g., C. S. Meinen et al., 2018; Smeed et al., 2018). A recent study which used the entire SAMBA moored array has shown that the amplitude of the AMOC max variability at 34.5°S is even larger than previously estimated with a standard deviation of 15.5 Sv for the upper‐cell and 6.2 Sv for the abyssal‐cell (Kersalé et al., 2020). The strongest variability occurs on timescales between 30 and 90 days tightly linked to the passage of eddies across the section (Kersalé et al., 2019).…”

Section: Introductionmentioning

confidence: 90%

“…Previous estimates of the AMOC max variability at this latitude from blended altimetry and XBT sections data (e.g., Dong et al., 2015) or Argo float data (e.g., Majumder et al., 2016) have revealed substantial seasonal to interannual variability, where the Ekman as well as the geostrophic transport contribution play a role both showing annual cycles, which are out of phase. The SAMBA‐SAMOC observations have also demonstrated a significant high‐frequency variability (Kersalé et al., 2020; C. S. Meinen et al., 2018). Both baroclinic (density) and barotropic (bottom pressure) variations at the eastern boundary at 34.5°S show significant or even dominant contributions to the overall AMOC variability at 34.5°S.…”

Section: Introductionmentioning

confidence: 99%

“…The SAMBA line of moorings began in a pilot mode in 2009, with a much better resolved array put in place beginning in 2013. SAMBA consists primarily of pressure‐equipped inverted echo sounders (PIES) and current‐and‐pressure‐equipped inverted echo sounders (CPIES), with four additional tall dynamic height/current meter moorings added on the South African continental margin in 2014 (e.g., Kersalé et al., 2018, 2020, 2019; C. S. Meinen et al., 2013; 2018). Hydrographic observations collected during the mooring maintenance cruises provide regional snapshots of the flow patterns and water mass regimes in the boundary regions.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, as no measurements exist inshore of 1,350 dbar on both boundaries, estimates in those shelf areas are also based on model velocities. As such, only the variability of AMOC max from the SAMBA PIES/CPIES array is a complete robust observational assessment (Kersalé et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

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The South Atlantic Meridional Overturning Circulation and Mesoscale Eddies in the First GO‐SHIP Section at 34.5°S

et al. 2021

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The variability of the Atlantic meridional overturning circulation (AMOC) has considerable impacts on the global climate system. Past studies have shown that changes in the South Atlantic control the stability of the AMOC and drive an important part of its variability. That is why significant resources have been invested in a South (S)AMOC observing system. In January 2017, the RV Maria S. Merian conducted the first GO-SHIP hydrographic transect along the SAMOC-Basin Wide Array (SAMBA) line at 34.5°S in the South Atlantic. This paper presents estimates of meridional volume, freshwater (MFT), and heat (MHT) transports through the line using the slow varying geostrophic density field and direct velocity observations. An upper and an abyssal overturning cell are identified with a strength of 15.64 ± 1.39 Sv and 2.4 ± 1.6 Sv, respectively. The net northward MHT is 0.27 ± 0.10 PW, increasing by 0.12 PW when we remove the observed mesoscale eddies with a climatology derived from the Argo floats data set. We attribute this change to an anomalous predominance of cold core eddies during the cruise period. The highest velocities are observed in the western boundary, within the Brazil and the Deep Western Boundary currents. These currents appear as a continuous deep jet located 150 km off the slope squeezed between two cyclonic eddies. The zonal changes in water masses properties and velocity denote the imprint of exchange pathways with both the Southern and the Indian oceans. Plain Language Summary The Atlantic meridional overturning circulation (AMOC) is a crucial element of the global ocean circulation and climate. It connects the Southern Ocean to the northern North Atlantic, and is responsible for the interhemispheric northward transport of heat and freshwater. The South Atlantic is a crossroad for water masses from the Southern, the Indian and the North Atlantic oceans. This paper analyzes the first full-ocean-depth trans-basin measurements of the southernmost enclosed section of the Atlantic between South Africa and Brazil along 34.5°S. Our results confirm a northward transport of heat at this latitude. We also found a complex water mass structure and dynamics, characterized by intense boundary currents and mesoscale eddies. It is the sum of these elements that is not only crucial for the Atlantic but also for the global ocean circulation and climate. MANTA ET AL.

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Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The South Atlantic Meridional Overturning Circulation and Mesoscale Eddies in the First GO‐SHIP Section at 34.5°S

et al. 2021

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“…The western tropical South Atlantic constitutes a key region for the exchange of water masses, heat and salt between the Southern Hemisphere and Northern Hemisphere (Biastoch et al, 2008b;Schmidtko and Johnson, 2012;Kolodziejczyk et al,2014;Hummels et al, 2015;Lübbecke et al, 2015;Herrford et al, 2017). Several observational and modelling studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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Abstract. Bottom pressure observations on both sides of the Atlantic basin, combined with satellite measurements of sea level anomalies and wind stress data, are utilized to estimate variations of the Atlantic Meridional Overturning Circulation (AMOC) at 11∘ S. Over the period 2013–2018, the AMOC and its components are dominated by seasonal variability, with peak-to-peak amplitudes of 12 Sv for the upper-ocean geostrophic transport, 7 Sv for the Ekman and 14 Sv for the AMOC transport. The characteristics of the observed seasonal cycles of the AMOC and its components are compared to results from an ocean general circulation model, which is known to reproduce the variability of the Western Boundary Current on longer timescales. The observed seasonal variability of zonally integrated geostrophic velocity in the upper 300 m is controlled by pressure variations at the eastern boundary, while at 500 m depth contributions from the western and eastern boundaries are similar. The model tends to underestimate the seasonal pressure variability at 300 and 500 m depth, especially at the western boundary, which translates into the estimate of the upper-ocean geostrophic transport. In the model, seasonal AMOC variability at 11∘ S is governed, besides the Ekman transport, by the geostrophic transport variability in the eastern basin. The geostrophic contribution of the western basin to the seasonal cycle of the AMOC is instead comparably weak, as transport variability in the western basin interior related to local wind curl forcing is mainly compensated by the Western Boundary Current. Our analyses indicate that while some of the uncertainties of our estimates result from the technical aspects of the observational strategy or processes not being properly represented in the model, uncertainties in the wind forcing are particularly relevant for the resulting uncertainties of AMOC estimates at 11∘ S.

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Opportunities for Earth Observation to Inform Risk Management for Ocean Tipping Points

Wood,

Baker,

Beaugrand

et al. 2024

Surv Geophys

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As climate change continues, the likelihood of passing critical thresholds or tipping points increases. Hence, there is a need to advance the science for detecting such thresholds. In this paper, we assess the needs and opportunities for Earth Observation (EO, here understood to refer to satellite observations) to inform society in responding to the risks associated with ten potential large-scale ocean tipping elements: Atlantic Meridional Overturning Circulation; Atlantic Subpolar Gyre; Beaufort Gyre; Arctic halocline; Kuroshio Large Meander; deoxygenation; phytoplankton; zooplankton; higher level ecosystems (including fisheries); and marine biodiversity. We review current scientific understanding and identify specific EO and related modelling needs for each of these tipping elements. We draw out some generic points that apply across several of the elements. These common points include the importance of maintaining long-term, consistent time series; the need to combine EO data consistently with in situ data types (including subsurface), for example through data assimilation; and the need to reduce or work with current mismatches in resolution (in both directions) between climate models and EO datasets. Our analysis shows that developing EO, modelling and prediction systems together, with understanding of the strengths and limitations of each, provides many promising paths towards monitoring and early warning systems for tipping, and towards the development of the next generation of climate models.

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Highly variable upper and abyssal overturning cells in the South Atlantic

Cited by 34 publications

References 38 publications

The South Atlantic Meridional Overturning Circulation and Mesoscale Eddies in the First GO‐SHIP Section at 34.5°S

The South Atlantic Meridional Overturning Circulation and Mesoscale Eddies in the First GO‐SHIP Section at 34.5°S

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

Opportunities for Earth Observation to Inform Risk Management for Ocean Tipping Points

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