Exchange of Pb from Indian to Atlantic Ocean is driven by Agulhas current and atmospheric Pb input from South Africa

Samanta, Saumik; Cloete, Ryan; Dey, Somnath; Barraqueta, Jan-Lukas Menzel; Loock, Jean; Meynecke, Jan‐Olaf; Bie, Jasper de; Vichi, Marcello; Roychoudhury, Alakendra N.

doi:10.1038/s41598-023-32613-5

Cited by 2 publications

(1 citation statement)

References 73 publications

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“…Anticyclonic eddies in other subtropical and mid-latitude regions have been observed to host elevated rates of N2 fixation (Holl et al, 2007;Fong et al, 2008;Löscher et al, 2016;Liu et al, 2020); similar conditions in the Cape Basin may favour N2 fixation, provided that the iron supply is sufficient (Deutsch et al, 2007;Marshall et al, 2022;Martin et al, 2024). Agulhas eddies do appear to host higher trace metal concentrations than the surrounding Atlantic because they include a significant contribution of southwest Indian Ocean coastal waters (Paul et al, 2015;Conway et al, 2016;Samanta et al 2023). However, the δ 15 NNO3 and Δ(15-18) of nitrate in the eddy mixed-layer and thermocline is higher than in the Agulhas Current (Fig.…”

Section: In-eddy N-cycling Processes: N2 Fixation and Ammonium Recyclingmentioning

confidence: 99%

Tracking Agulhas leakage in the South Atlantic using modern planktic foraminifera nitrogen isotopes

Granger,

Smart,

Foreman

et al. 2023

Preprint

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Seawater transported into the South Atlantic from the Indian Ocean via “Agulhas leakage” modulates global ocean circulation and has been linked to glacial-interglacial climate cycles. However, constraining past Agulhas leakage remains a challenge. Using new measurements from the modern South Atlantic, we propose that the δ15N of organic matter preserved in the shells of fossil planktic foraminifera could be used to infer past changes in Agulhas leakage. We sampled a transect of the Cape Basin in winter 2017 that intersected a mature Agulhas eddy and found that mixed-layer nitrate-, zooplankton-, and foraminifer-δ15N (tissue and shells) was 2-3‰ lower in the eddy than the background Atlantic even though the δ15N of the underlying thermocline nitrate was indistinguishable. We suggest that the δ15N of eddy-N reflects Agulhas Current thermocline nitrate, which is ~2‰ lower than that of the South Atlantic due to N2 fixation that occurs in the Indian Ocean. Foraminifera δ15N may have been further lowered during eddy migration by in-situ N2 fixation and/or recycling of low-δ15N ammonium. The absence of low-δ15N Agulhas nitrate in the eddy thermocline can be explained by convective mixing of thermocline and mixed layer waters at the Agulhas Current Retroflection where eddies form, and the subsequent consumption of Agulhas nitrate by phytoplankton in the mixed layer, which raises its δ15N. The low δ15N of eddy foraminifera, apparent even after several months of eddy migration across the Cape Basin, suggests that fossil foraminifer-bound δ15N from the region may record variations in past Agulhas leakage.

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Section: In-eddy N-cycling Processes: N2 Fixation and Ammonium Recyclingmentioning

confidence: 99%

Tracking Agulhas leakage in the South Atlantic using modern planktic foraminifera nitrogen isotopes

Granger,

Smart,

Foreman

et al. 2023

Preprint

View full text Add to dashboard Cite

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Winter entrainment drives the mixed layer supply of manganese in the Southern Ocean

Ramalepe,

Samanta,

Cloete

et al. 2024

Limnology & Oceanography

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Despite the subnanomolar dissolved manganese concentrations that can co‐limit Southern Ocean primary production, their physical supply mechanisms during winter, for biological consumption in spring and summer have not yet been explored. During austral winter and spring 2019, two cruises were conducted in the Atlantic sector of the Southern Ocean, to determine the distribution and surface water supply mechanisms of dissolved manganese in the upper water column. The supply mechanisms were used to calculate the total flux of dissolved manganese to productive surface waters and were compared to biological consumption estimates. Mean dissolved manganese concentrations in the upper water column (< 500 m) during winter and spring were comparably low (≤ 0.34 nmol kg−1; p > 0.05), with seasonal mixed layer reservoir sizes averaging 65.21 ± 12.93 and 21.64 ± 19.32 μmol m−2, respectively. Winter entrainment contributed 89.33–99.99% (average 97.26% ± 5.28%) of the total dissolved manganese flux, while diapycnal diffusion contributed 0.52–10.58% (average 4.92% ± 5.14%), was identified as the dominant mechanisms for transporting dissolved manganese into the mixed layer in the subantarctic zone, polar frontal zone, and antarctic zone. Here, the winter physical supply rates were higher than the estimated consumption rates during spring, meeting phytoplankton biological demands. Whereas in the subtropical zone, the supply rates were lower than the consumption rates, indicating the presence of additional supply mechanisms such as coastal upwelling, which may help to meet the biological demands in this region.

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Exchange of Pb from Indian to Atlantic Ocean is driven by Agulhas current and atmospheric Pb input from South Africa

Cited by 2 publications

References 73 publications

Tracking Agulhas leakage in the South Atlantic using modern planktic foraminifera nitrogen isotopes

Tracking Agulhas leakage in the South Atlantic using modern planktic foraminifera nitrogen isotopes

Winter entrainment drives the mixed layer supply of manganese in the Southern Ocean

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