The Surface Pathways of the South Atlantic: Revisiting the Cold and Warm Water Routes Using Observational Data

Drouin, Kimberley L.; Lozier, M. Susan

doi:10.1029/2019jc015267

Cited by 13 publications

(17 citation statements)

References 59 publications

(149 reference statements)

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“…Richardson () found similar leakage percentages: 23% for the ALACE floats, 18% for the RAFOS floats, and 33% for the GDP drifters. Our results and his are very different from those of Drouin and Lozier () who found that less than 10% of drifters leaked. The inconsistency comes mainly in their denominator, which includes drifters outside the southwestward flow of the Agulhas Current which are not heading into the retroflection, as well as those that remain in the retroflection region, which we discount on the basis that we cannot be sure whether they eventually leak or not.…”

Section: Resultscontrasting

confidence: 99%

“…We have found that retaining these resident drifters in simulations makes results sensitive to the lifetime of the particles (Cheng et al, ). Drouin and Lozier () also find that the drifter leakage percentage is very sensitive to the latitude used to define the Agulhas Current crossing with a decrease in leakage as the latitude is moved upstream. Taking only those drifters that pass through 32°S, however, we find nearly the same percentage of undrogued (12/36, 33%) and drogued drifters (8/25, 32%) that leak.…”

Section: Resultsmentioning

confidence: 96%

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A New Improved Estimation of Agulhas Leakage Using Observations and Simulations of Lagrangian Floats and Drifters

2020

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A new estimate of Agulhas leakage transport is calculated using profiling floats and drifters.Since Richardson's seminal estimate of 15 Sv in 2007, the number of floats and drifters passing through the Agulhas Current has quadrupled. Within uncertainties we find the same leakage percentages as Richardson, with 34% of drifters leaking at the surface and 21% of floats leaking at 1,000 m depth. We find that the drifters tend to follow a northward leakage pathway via the Benguela Current compared to the northwestward leakage pathway of the floats along the Agulhas Ring corridor. We simulate the isobaric and profiling behavior of the floats and drifters using two high resolution models and two offline Lagrangian tracking tools, quantifying for the first time the sampling biases associated with the observations. We find that the isobaric bias cannot be robustly simulated but likely causes an underestimate of observed leakage by one or two Sverdrups. The profiling behavior of the floats causes no significant bias in the leakage. Fitting a simulated vertical leakage profile to the observed leakage percentages from the floats and drifters and using the mean Agulhas transport observed by a moored array at 34 • S we find an improved Agulhas leakage transport of 21.3 Sv, with an estimated error of 4.7 Sv. Our new leakage transport is higher primarily because we account for leakage at depths down to 2,000 m, while Richardson considered only the top 1,000 m of the water column. Plain Language SummaryWe calculate a new estimation of Agulhas leakage using floats and drifters. Since most recent estimate of 15 Sv was calculated in 2007, we have had four times as many observations pass through the Agulhas Current. We find more drifters leak at the surface than floats at intermediate depth. The drifters follow a northward leakage passage compared to the northwestward passage of the floats. Using two models and two particle tracking tools, we mimic the behavior of these floats and drifters to better understand and quantify the sampling biases associated with these observations. Combining the results from the observations and these simulations, we calculate a new improved leakage transport of 21.3 Sv with an error of 4.7 Sv.Quantifying Agulhas leakage is difficult, with previous estimates ranging from 2 to 20 Sv (1 Sv = 1 × 10 6 m 3 s −1 ). The Cape Basin features the highest eddy kinetic energy outside a western boundary current system in the world (Chelton et al., 2011). Due to this highly turbulent nature, the mixing and stirring

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Section: Resultscontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 96%

A New Improved Estimation of Agulhas Leakage Using Observations and Simulations of Lagrangian Floats and Drifters

2020

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“…Natural remanent magnetization (NRM) was measured and stepwise demagnetized with a superconducting 2G Enterprises 755 SRM long-core magnetometer. Demagnetization was accomplished in 10 steps at AF peak levels of 5,10,15,20,30,40,50,65,80, and 100 mT. NRM results were analysed with principle component analysis 63 to determine direction of the characteristic remanent magnetization (ChRM).…”

Section: Methodsmentioning

confidence: 99%

“…Core PS67/197-1 in the Scotia Sea is sensitive to changes in winter sea ice extent 17 . Light blue arrows show the Antarctic Circumpolar Current (ACC), the Cape Horn Current (CHC) 19 and Malvinas Current (MC) 20 , while dark green-blue arrows are Weddell Sea Bottom Water (WSBW, thick) and Weddell Sea Deep Water (WSDW, thin) flows 21 . White dotted line is average modern winter sea ice edge 22 .…”

mentioning

confidence: 99%

Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

Lembke‐Jene

Lamy

et al. 2020

Preprint

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The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

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“…For the description given hereafter, the reader who is not familiar with South Atlantic large-scale circulations and its ocean currents is referred to Figure 3 from , to aid visual interpretation. (R ühs et al, 2019;Drouin and Lozier, 2019;.…”

Section: Characterization Of the General Mean Circulation Fieldmentioning

confidence: 99%

Past to Future South Atlantic Overturning Circulation: upper-ocean pathways and low-frequency variability

Oliveira¹

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The Surface Pathways of the South Atlantic: Revisiting the Cold and Warm Water Routes Using Observational Data

Cited by 13 publications

References 59 publications

A New Improved Estimation of Agulhas Leakage Using Observations and Simulations of Lagrangian Floats and Drifters

A New Improved Estimation of Agulhas Leakage Using Observations and Simulations of Lagrangian Floats and Drifters

Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

Past to Future South Atlantic Overturning Circulation: upper-ocean pathways and low-frequency variability

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