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Glacial and hydrothermal sources of dissolved iron(II) in Southern Ocean waters surrounding Heard and McDonald Islands
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  • Thomas Michael Holmes,
  • Kathrin Wuttig,
  • Zanna Chase,
  • Christina Schallenberg,
  • Pier van der Merwe,
  • Ashley T Townsend,
  • Andrew Bowie
Thomas Michael Holmes
Antarctic Climate and Ecosystems Cooperative Research Centre

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Kathrin Wuttig
Antarctic Climate and Ecosystems Cooperative Research Centre
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Zanna Chase
University of Tasmania
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Christina Schallenberg
ACE CRC
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Pier van der Merwe
Antarctic Climate and Ecosystem Cooperative Research Centre, University of Tasmania
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Ashley T Townsend
University of Tasmania
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Andrew Bowie
University of Tasmania
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Abstract

The Southern Ocean is the largest region in which iron limits the growth of phytoplankton. However, a phytoplankton bloom thousands of square kilometres in area forms each spring-summer in the Indian sector of the Southern Ocean, both above and to the east of the Kerguelen Plateau. The central region of the Kerguelen Plateau hosts the volcanically active islands, Heard and McDonald (HIMI), the former of which is largely covered by glaciers. The sources and processes governing supply of iron from HIMI to the region are relatively unknown. In the austral summer of 2016, the first voyage to focus on biogeochemical cycling in the HIMI region was undertaken (GEOTRACES process study GIpr05). Using iron redox measurements, we show here that each of the adjacent islands are strong sources of dissolved iron(II) (DFe(II)), though controlled by different supply mechanisms.
At Heard Island, the greatest DFe(II) concentrations (max 0.57 nmol L) were detected north of the island. An inverse correlation of DFe(II) concentrations with salinity suggests the origin is from a sea-terminating glacier on the island. At McDonald Islands, the greatest DFe(II) concentrations (max 1.01 nmol L) were detected east of the islands which, based on DFe(II) profiles from five targeted stations, appears likely to originate from shallow diffuse hydrothermalism. Elevated DFe(II) around HIMI may increase Fe availability for biota and indicate slower oxidation kinetics in the region, which has implications for transport of Fe away from the islands to the broader northern Kerguelen Plateau where the annual plankton bloom is strongest.
Oct 2020Published in Journal of Geophysical Research: Oceans volume 125 issue 10. 10.1029/2020JC016286