Preprints
https://doi.org/10.5194/bg-2020-42
https://doi.org/10.5194/bg-2020-42

  06 Mar 2020

06 Mar 2020

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

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

Neil J. Wyatt1, Angela Milne2, Eric P. Achterberg3, Thomas J. Browning3, Heather A. Bouman4, E. Malcolm S. Woodward5, and Maeve C. Lohan1 Neil J. Wyatt et al.
  • 1Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
  • 2School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, UK
  • 3Marine Biogeochemistry Division, GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
  • 4Department of Earth Sciences, University of Oxford, Oxford, UK
  • 5Plymouth Marine Laboratory, Plymouth, UK

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.

Neil J. Wyatt et al.

 
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Neil J. Wyatt et al.

Neil J. Wyatt et al.

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Short summary
Using data collected during two expeditions to the South Atlantic ocean, we investigated how the interaction between external sources and biological activity influenced the availability of the trace metals zinc and cobalt. This is important as both metals play essential roles in the metabolism and growth of phytoplankton and thus influence primary productivity of the oceans. We found seasonal changes in both processes that helped explain upper ocean trace metal cycling.
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