Tracing the Agulhas leakage with lead isotopes

Paul, Maxence; Flierdt, Tina van de; Rehkämper, Mark; Khondoker, Roulin; Weiss, Dominik; Lohan, Maeve C.; Homoky, William B.

doi:10.1002/2015gl065625

Cited by 25 publications

(25 citation statements)

References 34 publications

(54 reference statements)

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“…Indian ocean water is transported into the Atlantic within the Agulhas retroflection, typically in the form of large anticyclonic eddies ('Agulhas rings'; Lutjeharms, 2006). Such rings, characterized both on the GA10 and GIPY4 cruises by elevated temperature, salinity and nutrients (S >35; T 15-23°C; Arhan et al, 2011;Wyatt et al, 2014), can have an important effect on both biogeochemical cycling in surface waters (Viller et al, 2015); indeed, it was recently shown that Agulhas rings transport an Indian Ocean Pb isotope signature to the North Atlantic (Paul et al, 2015), suggesting that they could also play a role in influencing the surface ocean cycling of Fe and other trace metals.…”

Section: Gipy4 (2008) and Ga10 (2010)mentioning

confidence: 99%

Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean

2016

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Intercomparison of trace metal data is a key aspect of the International GEOTRACES program, allowing data from multiple laboratories and countries to be combined to produce high-resolution datasets for the oceans. The use of crossover stations by the GEOTRACES program provides the opportunity both for comparison of analytical techniques and assessment of temporal variability in the cycling of trace metals such as iron (Fe). Here, we present the first comparison of dissolved Fe stable isotope ratio (δ 56 Fe; relative to IRMM-014) profiles in the oceans, from re-occupations of three locations in the Atlantic Ocean; (1) the Bermuda Atlantic Time Series Station (31.75°N 64.17°W) during the U.S. GEOTRACES IC1 cruise (June 2008) and the U.S. GEOTRACES GA03 cruise (Nov. 2011); (2) a station near Cape Verde (17.4°N 24.5°W) during the U.S GEOTRACES GA03 cruises (2010; 2011), and (3) two nearby stations in the Cape Basin close to South West Africa (31.1-31.4°S 36.5°W) during the French GEOTRACES GIPY4 Bonus Good Hope Cruise (Feb. 2008) and the U.K. GEOTRACES GA10 D357 cruise (Oct. 2010). These datasets provided us with the opportunity not only to compare sampling and analysis techniques by two different laboratories (USC and LEGOS), but also the temporal variability of δ 56 Fe at these locations on a 1-3 year timescale. A good agreement between data and profiles generated by different laboratories does allows assessment of temporal variation of δ 56 Fe in the water column, as well as spatial variability and synthesis of datasets from different regions of the ocean. Comparison of δ 56 Fe at the three locations in this study demonstrates a remarkable consistency between the shape of ocean δ 56 Fe profiles measured 1-3 years apart, pointing to the overall stability of Fe cycling at all three locations on these timescales, despite the expected dynamic nature of the Fe cycle. This consistency is highlighted by strong agreement in δ 56 Fe throughout the whole water-column at Bermuda, and in waters deeper than 500 m in the Cape Basin, which suggests that different water masses may carry distinct δ 56 Fe signatures. In contrast to the stable δ 56 Fe at these locations, we observe some apparent variability in δ 56 Fe between cruises at other locations, both throughout the water column at Cape Verde, and in Agulhas-leakage influenced surface waters in the Cape Basin. Such variability may provide information about changes in internal Fe cycling or external Fe sources on these timescales. Overall, this study highlights the usefulness of repeat δ 56 Fe

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Section: Gipy4 (2008) and Ga10 (2010)mentioning

confidence: 99%

Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean

2016

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“…CC BY 4.0 License. et al, 2019) as well as interactions with shelf and slope waters of the Agulhas Bank (Bown et al, 2011;Boye et al, 2012;Paul et al, 2015). During the D357 spring transects, elevated mixed-layer dZn and dCo concentrations (up to 4.57 nM and 50 pM, respectively; Sect.…”

Section: Shelf Derived Sources Of Zn and Comentioning

confidence: 98%

“…Intermediate Water (AAIW) were identified using their characteristic core potential density (σθ 26.8 kg m -3 ) (Sarmiento et al, 2004;Palter et al, 2010) (Chever et al, 2010;Bown et al, 2011;Boye et al, 2012;Paul et al, 2015). We postulate that these trace metal enrichments can arise from either atmospheric inputs, and/or from the lateral advection of metal-enriched waters from the Agulhas Current (AC) and/or South African continental shelf.…”

Section: Sub-surface Watersmentioning

confidence: 99%

“…These inputs are low compared with the mixed-layer metal inventories, representing <1 % of dZn and dCo in STSW during the D357 transects (Table 2), and would not be sufficient to generate distinct mixedlayer maxima. It is likely, therefore, that the dZn and dCo elevations originated from the advection of metal-enriched waters from the western Agulhas Bank, a region identified as a distinct source of both dissolved and particulate trace metals to the Southeast Atlantic (Chever et al, 2010;Bown et al, 2011;Boye et al, 2012;Paul et al, 2015), and/or from the leakage of Indian Ocean water into the Southeast Atlantic via the AC.…”

Section: Shelf Derived Sources Of Zn and Comentioning

confidence: 99%

“…The detachment of Agulhas rings and filaments from the AC during its retroflection back towards the Indian Ocean constitutes a source of Pb to the surface Southeast Atlantic along the D357 transects (Paul et al, 2015). Whilst we observed elevated mixed-layer dZn and dCo at ~15ºE during both D357 transects, the absence of metal enrichment across the depth of the AC salinity maxima (Figs.…”

Section: Shelf Derived Sources Of Zn and Comentioning

confidence: 99%

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Seasonal cycling of zinc and cobalt in the Southeast Atlantic along the GEOTRACES GA10 section

Wyatt¹,

Milne²,

Achterberg³

et al. 2020

Preprint

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Abstract. We report the distributions of dissolved zinc (dZn) and cobalt (dCo) in sub-tropical and sub-Antarctic waters of the Southeast Atlantic Ocean during austral spring 2010 and summer 2011/12. A strong seasonal signal was observed in sub-tropical surface waters with early spring mixed-layer dZn and dCo concentrations of 3.16 ± 1.35 nM and 39 ± 9 pM, respectively, compared with summer values depleted well below these levels by biological activity. The elevated spring mixed-layer dZn concentrations resulted from an apparent offshore transport of elevated dZn at depths between 20–50 m, derived from lithogenic inputs from the Agulhas Bank. In contrast, open-ocean sub-Antarctic surface waters displayed largely consistent inter-seasonal mixed-layer dZn and dCo concentrations of 0.11 ± 0.08 nM and 11 ± 5 pM, respectively. The vertical distributions of dZn and dCo in the upper water column were similar to that of phosphate (PO43−), with positive linear relationships during each of the seasons and across dynamic biogeochemical regimes, suggesting surface biological drawdown and shallow remineralisation of these metals in this region largely influences their distribution. The ecological stoichiometries for dZn and dCo, calculated from the linear regression with PO43−, suggest a greater overall use of dZn relative to dCo in the upper water column of the Southeast Atlantic with an inter-seasonal Zn:Co ratio ranging between 9 and 29. Sub-tropical surface water Zn:Co ratios were found to decrease between spring and summer indicating a preferential removal of dZn relative to dCo between seasons. In this paper we investigate how the seasonal influences of external input and phytoplankton succession may relate to the distribution of dZn and dCo, and variation in Zn:Co ecological stoichiometry, across two distinct ecological regimes in the Southeast Atlantic.

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Efficient extraction of past seawater Pb and Nd isotope signatures from Southern Ocean sediments

Huang

Gutjahr

Kuhn

et al. 2020

Preprint

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Tracing the Agulhas leakage with lead isotopes

Cited by 25 publications

References 34 publications

Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean

Intercomparison of dissolved iron isotope profiles from reoccupation of three GEOTRACES stations in the Atlantic Ocean

Seasonal cycling of zinc and cobalt in the Southeast Atlantic along the GEOTRACES GA10 section

Efficient extraction of past seawater Pb and Nd isotope signatures from Southern Ocean sediments

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