Cycling of Zinc and Its Isotopes across Multiple Zones of the Southern Ocean: Insights from the Antarctic Circumnavigation Expedition

M. Sieber, T. M. Conway, G. F. de Souza, C. S. Hassler, M. J. Ellwood, D. Vance

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Abstract

<p> <p id="x-x-sp0005"> Zinc (Zn) is an essential micronutrient, playing an important role in several key processes in marine <a title="Learn more about phytoplankton from ScienceDirect's AI-generated Topic Pages"> phytoplankton </a> . Here, we present the first high-resolution depth profiles for dissolved Zn and &delta; <sup> 66 </sup> Zn from all major zones of the <a title="Learn more about Southern Ocean from ScienceDirect's AI-generated Topic Pages"> Southern Ocean </a> , collected during the Antarctic Circumnavigation Expedition in Austral Summer 2016/2017. The dataset reveals that Zn cycling changes between different regions of the Southern Ocean. Within the Antarctic <a title="Learn more about Circumpolar Current from ScienceDirect's AI-generated Topic Pages"> Circumpolar Current </a> (ACC), Zn cycling is closely linked to phosphate (PO <sub> 4 </sub> ), governed by uptake and regeneration, seasonal mixing, and upwelling. Here, uptake by phytoplankton is associated with a very small fractionation (&alpha; = 0.99995), resulting in slightly elevated surface &delta; <sup> 66 </sup> Zn (up to +0.67&permil;), overlying a shallow subsurface &delta; <sup> 66 </sup> Zn minimum (+0.36&permil; at &sim;200 m). South of the ACC, a partial coupling of Zn and silicate (Si) results in a shift of the <a title="Learn more about Zn isotope from ScienceDirect's AI-generated Topic Pages"> Zn isotope </a> systematics and a deep enrichment of Zn and Si. Two possible mechanisms could potentially cause this change: 1) reversible scavenging onto sinking particulates, or, 2) association of isotopically heavy Zn with diatom frustules. We also observe the effects of regional processes on Zn in the surface Southern Ocean: firstly, natural Fe fertilization near the Balleny Islands appears to lead to reduced Zn uptake (relative to phosphate) by phytoplankton, that is associated with a greater apparent Zn isotope fractionation than elsewhere in the Southern Ocean (&alpha; = 0.99987); secondly, <a title="Learn more about meltwater from ScienceDirect's AI-generated Topic Pages"> meltwater </a> inputs from the Mertz Glacier add small amounts of isotopically light Zn to surface waters near the Antarctic shelf. Overall, we propose that the lack of distinct &delta; <sup> 66 </sup> Zn signatures transported in intermediate waters of the lower latitude global oceans is due to near-complete uptake of Zn by phytoplankton in the surface Southern Ocean with only a small isotope fractionation, in contrast to elements like cadmium and silicon. </p></p>
Original languageAmerican English
JournalGeochimica et Cosmochimica Acta
Volume268
DOIs
StatePublished - Jan 1 2020

Keywords

  • Trace metals
  • Biogeochemistry
  • Zinc
  • Antarctic circumpolar current
  • Isotopes
  • Nutrient cycling

Disciplines

  • Life Sciences

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