Isotopic Fingerprinting of Biogeochemical Processes and Iron Sources in the Iron-limited Surface Southern Ocean

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

Research output: Contribution to journalArticlepeer-review

Abstract

<p> <p id="x-x-sp0090"> Iron (Fe) is an essential micronutrient that limits primary productivity throughout the surface of the <a title="Learn more about Southern Ocean from ScienceDirect's AI-generated Topic Pages"> Southern Ocean </a> . Here, we present the first high-resolution depth profiles for dissolved Fe and Fe <a title="Learn more about isotope ratios from ScienceDirect's AI-generated Topic Pages"> isotope ratios </a> (&delta;56"&gt;&delta;56 Fe) from all major zones of the Southern Ocean, collected during the Antarctic Circumnavigation Expedition in austral summer 2017. Open-ocean surface waters are characterized by remarkably high &delta;56"&gt;&delta;56 Fe values (up to +1.6&permil;) and very low Fe concentrations (&lt;0.05 nmol kg <sup> &minus;1 </sup> ). We attribute the elevated &delta;56"&gt;&delta;56 Fe values above the ferricline to the effect of continuous shallow cycling processes (uptake, recycling, and binding of Fe to organic ligands), with only a very limited resupply of Fe from below. Below the ferricline, &delta;56"&gt;&delta;56 Fe values approach &sim;0&permil; and remain constant down to our deepest samples at 1000 m, with no obvious isotope signal from regeneration. This overall pattern in &delta;56"&gt;&delta;56 Fe is modified near islands, <a title="Learn more about continental shelves from ScienceDirect's AI-generated Topic Pages"> continental shelves </a> and <a title="Learn more about hydrothermal vents from ScienceDirect's AI-generated Topic Pages"> hydrothermal vents </a> , where distinct &delta;56"&gt;&delta;56 Fe signatures are associated with different Fe sources. Near the volcanic Balleny Islands, elevated surface Fe concentrations associated with low &delta;56"&gt;&delta;56 Fe are indicative of reductive release of isotopically light Fe from sediments. Elevated &delta;56"&gt;&delta;56 Fe values at depth near the Balleny <a title="Learn more about seamount from ScienceDirect's AI-generated Topic Pages"> seamount </a> chain and near the East Scotia Arc may reflect distal hydrothermal influences, caused by fractionation associated with precipitation or the loss of specific phases of Fe during long-range transport. Sedimentary sources of isotopically light Fe on the Antarctic <a title="Learn more about Peninsula from ScienceDirect's AI-generated Topic Pages"> Peninsula </a> are important for shelf waters. Long-distance transport of this sediment-derived Fe and its influence on surface waters are strongly dependent on the regional circulation, and may ultimately be the source of light Fe previously observed within <a title="Learn more about Antarctic Intermediate Water from ScienceDirect's AI-generated Topic Pages"> Antarctic Intermediate Water </a> in the Atlantic sector of the Southern Ocean. </p></p>
Original languageAmerican English
JournalEarth and Planetary Science Letters
Volume567
DOIs
StatePublished - Jan 1 2021

Keywords

  • trace metals
  • micronutrients
  • biogeochemistry
  • nutrient cycling
  • Antarctic Circumnavigation Expedition

Disciplines

  • Life Sciences

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