Formation and Transport of the South Atlantic Subtropical Mode Water in Eddy‐Permitting Observations

Chen, Yanxu; Speich, Sabrina; Laremxenaire, Rémi

doi:10.1029/2021jc017767

Cited by 16 publications

(15 citation statements)

References 83 publications

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“…Our Type I MW relates to the most saline variety (SASTMW2), and the Type II MW to the densest variety (SASTMW3). Corroborating the conclusions of ; Chen et al (2022) demonstrated that, contrary to the findings of Smythe-Wright et al (1996), a ring in the southeast Atlantic carrying MW with a potential temperature of 13°C and salinity of 35.2 psu originated at the Agulhas Retroflection and not at the Brazil-Malvinas Confluence as initially supposed, corroborating the conclusions of . Whether the 12-13°C thermostad, by origin, is subantarctic or subtropical, from a remote site in the South Indian Ocean, or locally formed, remains controversial and deserves more research.…”

Section: Discussionsupporting

confidence: 74%

“…Using numerical modeling, Capuano et al (2018) demonstrated the role of turbulence and instabilities in the Cape Basin on the transformation of water masses from the Indian Ocean and subduction of MW inside Agulhas rings. Using a new algorithm to detect MW in Argo profiles, including outcropping MW, Chen et al (2022) suggested a new interpretation of the origin and formation of the MWs found in the upper thermocline of the South Atlantic Ocean. Their results led to a redefinition of the three types of South Atlantic STMW, where the origins of both the lightest and the densest varieties were found mainly inside the southeastern Cape Basin, related to the Agulhas Leakage, while Sato and Polito (2014) argued that two varieties are related to the Brazil-Malvinas Confluence.…”

Section: Introductionmentioning

confidence: 99%

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Observing the spread of Agulhas Leakage into the Western South Atlantic by tracking mode waters within ocean rings

2022

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The Agulhas rings transport warm and salty waters that feed the surface limb of the Atlantic Meridional Overturning Circulation. Some studies have focused on the conveying capacity of ocean eddies, and recently, the role of the Agulhas rings in advecting water masses and organisms has been explored. Here we show evidence that the Agulhas rings are responsible for the advection of mode waters from the Cape Basin to the western side of the Atlantic. We analyzed more than 3,200 temperature profiles and 2,400 salinity profiles from historical databases collocated with 52 long-lived Agulhas rings tracked from 1993 through 2016. An automated algorithm was used to identify thermostads in the profiles acquired within the rings. The data revealed mode water layers trapped inside 88% of the rings. The joint distribution of temperature and salinity indicated two types of mode waters in the range 16.2 ± 0.6°C, 35.6 ± 0.1 (Type I) and 12.9 ± 0.7°C, 35.2 ± 0.1 (Type II). The majority (67%) of the rings carrying mode waters had both types detected inside. Moreover, considering only those rings sampled west of the Mid-Atlantic Ridge, we found that 45% of them advected mode waters to the western basin. Therefore, our results demonstrate that, despite the long journey, interaction with the bottom topography and other vortices, ocean-atmosphere exchanges, and decay, the Agulhas rings are responsible for spreading mode waters initially available at the Cape Basin throughout the South Atlantic, contributing to a positive anomaly in temperature and salinity along the eddy corridor joining the Cape Basin to the Brazil Basin.

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Section: Discussionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Observing the spread of Agulhas Leakage into the Western South Atlantic by tracking mode waters within ocean rings

2022

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“…A winter with strong heat loss is expected to deepen MLD a lot, including inside-eddy, and a subsequently warmer winter could then not achieve to deepen the MLD as much. This mechanism drives mode-water formation, and it was already shown in other regions, mostly the Atlantic Ocean, that eddies could modulate mode-water formation (Dugan et al, 1982;Chen et al, 2022). Such hypothesis could also explain the high occurrence of 'non-connecting' events in the Mediterranean sea, this region being known for a high interannual variability of winter heat loss.…”

Section: Double-core Eddy Formationmentioning

confidence: 77%

How subsurface and double-core anticyclones intensify the winter mixed layer deepening in the Mediterranean sea

Barboni

Coadou-Chaventon

Stegner

et al. 2022

Preprint

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Abstract. The mixed layer is the uppermost layer of the ocean, driven by atmospheric fluxes. It follows a strong seasonal cycle, deepening in winter due to buoyancy loss, shoaling very close to the surface with summer restratification. Recently global and regional studies showed a mixed layer depth (MLD) modulation by mesoscale eddies with the seasonal cycle. In winter, MLD tends to be deeper inside anticyclonic eddies and shallower inside cyclonic ones. Several studies proposed a scaling law with eddy sea surface height deviation. However they were done globally or regionally with eddy composites mostly representative of surface-intensified structures and using monthly averaged climatologies as reference. The Mediterranean sea contains a wide variety of mesoscale eddies, with the specific presence of several large anticyclones living up to 4 years, in particular in the Eastern basin. These anticyclones were surveyed over the past decade with numerous Argo floats deployments. Several floats remained trapped inside anticyclones for months and enabled to record 16 continuous MLD time series inside 13 long-lived anticyclones at a fine temporal scale on the order of the week. MLD evolution at anticyclone cores reveals a stronger winter deepening, reaching sometimes deeper than 300 m, compared to always less than 100 m in the neighboring background. MLD evolution also does not coincide inside- and outside-eddy, starting to restratify outside of eddies, while it keeps deepening and cooling MLD at anticyclone core for a longer time. We then bring to light a restratification delay of one month on average between the anticyclones and their background, sometimes reaching more than 2 months. Extreme MLD anomalies of up to 330 m that would be smoothed in composite analyses can then be observed when the winter mixed layer connects with a preexisting subsurface anticyclonic core, greatly accelerating mixed layer deepening. On the opposite, the winter MLD sometimes does not achieve such connection but homogenizes a second subsurface layer, then forming a double-core anticyclone with spring restratification. Formation of several double-core anticyclones in the Eastern Mediterranean is accurately described in time. MLD restratification delay and connection with preexisting subsurface anomalies appear to be determinant in MLD modulation by mesoscale eddy and highlights the importance of interaction with eddy vertical structure.

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“…2c; Table 1). South Atlantic Central Waters (SACW) are produced locally as they originate from the subduction of subtropical Mode Waters in hotspots of air-sea interaction and eddy activity in the southwestern Atlantic at the Brazil-Malvinas Confluence (BMC) and the southeastern Atlantic 127,128 (Box 1). These two regional hotspots also encompass pathways whereby relatively fresh and highly oxygenated intermediate waters enter the South Atlantic.…”

Section: Box 1 | Observing the Overturning Circulation In The South A...mentioning

confidence: 99%

“…Despite its small area, upper ocean warming in the South Atlantic accounts for roughly 10% of global upper ocean warming. Some of this excess heat has been taken up by subtropical Atlantic mode waters since nearly 1980, which then ventilate the main thermocline and transport heat away from the surface 128,138,148,149 . South Atlantic AAIW properties also show significant warming, and their salinity seems to be decreasing over the past few decades 148,150 (Fig.…”

Section: Box 1 | Observing the Overturning Circulation In The South A...mentioning

confidence: 99%

Energetic overturning flows, dynamic interocean exchanges, and ocean warming observed in the South Atlantic

Chidichimo

Perez

Speich

et al. 2023

Commun Earth Environ

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Since the inception of the international South Atlantic Meridional Overturning Circulation initiative in the 21st century, substantial advances have been made in observing and understanding the Southern Hemisphere component of the Atlantic Meridional Overturning Circulation (AMOC). Here we synthesize insights gained into overturning flows, interocean exchanges, and water mass distributions and pathways in the South Atlantic. The overturning circulation in the South Atlantic uniquely carries heat equatorward and exports freshwater poleward and consists of two strong overturning cells. Density and pressure gradients, winds, eddies, boundary currents, and interocean exchanges create an energetic circulation in the subtropical and tropical South Atlantic Ocean. The relative importance of these drivers varies with the observed latitude and time scale. AMOC, interocean exchanges, and climate changes drive ocean warming at all depths, upper ocean salinification, and freshening in the deep and abyssal ocean in the South Atlantic. Long-term sustained observations are critical to detect and understand these changes and their impacts.

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Formation and Transport of the South Atlantic Subtropical Mode Water in Eddy‐Permitting Observations

Cited by 16 publications

References 83 publications

Observing the spread of Agulhas Leakage into the Western South Atlantic by tracking mode waters within ocean rings

Observing the spread of Agulhas Leakage into the Western South Atlantic by tracking mode waters within ocean rings

How subsurface and double-core anticyclones intensify the winter mixed layer deepening in the Mediterranean sea

Energetic overturning flows, dynamic interocean exchanges, and ocean warming observed in the South Atlantic

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