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> (δ56">δ56 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 δ56">δ56 Fe values (up to +1.6‰) and very low Fe concentrations (<0.05 nmol kg <sup> −1 </sup> ). We attribute the elevated δ56">δ56 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, δ56">δ56 Fe values approach ∼0‰ and remain constant down to our deepest samples at 1000 m, with no obvious isotope signal from regeneration. This overall pattern in δ56">δ56 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 δ56">δ56 Fe signatures are associated with different Fe sources. Near the volcanic Balleny Islands, elevated surface Fe concentrations associated with low δ56">δ56 Fe are indicative of reductive release of isotopically light Fe from sediments. Elevated δ56">δ56 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 language | American English |
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Journal | Earth and Planetary Science Letters |
Volume | 567 |
DOIs | |
State | Published - Jan 1 2021 |
Keywords
- trace metals
- micronutrients
- biogeochemistry
- nutrient cycling
- Antarctic Circumnavigation Expedition
Disciplines
- Life Sciences