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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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Holmes, TM ORCID: 0000-0001-8061-4325, Wuttig, K ORCID: 0000-0003-4010-5918, Chase, Z ORCID: 0000-0001-5060-779X, Schallenberg, C ORCID: 0000-0002-3073-7500, van der Merwe, P ORCID: 0000-0002-7428-8030, Townsend, AT ORCID: 0000-0002-2972-2678 and Bowie, AR ORCID: 0000-0002-5144-7799 2020 , 'Glacial and hydrothermal sources of dissolved iron(II) in Southern Ocean waters surrounding Heard and McDonald Islands' , Journal of Geophysical Research: Oceans, vol. 125, no. 10 , pp. 1-16 , doi: 10.1029/2020JC016286.

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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 dissolved iron (II) (DFe (II)) and hydrogen peroxide (H2O2) measurements, we are able to resolve iron sources and show that each of the adjacent islands are strong sources of reduced iron, though controlled by different supply mechanisms. At Heard Island, the greatest DFe (II) concentrations (0.57 nmol L‐1) 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 (1.01 nmol L‐1) 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 has implications for transport of Fe away from the islands to the broader northern Kerguelen Plateau where the annual plankton bloom is strongest.

Item Type: Article
Authors/Creators:Holmes, TM and Wuttig, K and Chase, Z and Schallenberg, C and van der Merwe, P and Townsend, AT and Bowie, AR
Keywords: GEOTRACES, biogeochemistry, iron, trace metal, Southern Ocean, Kerguelen Plateau
Journal or Publication Title: Journal of Geophysical Research: Oceans
Publisher: Wiley-Blackwell Publishing Inc.
ISSN: 2169-9291
DOI / ID Number: 10.1029/2020JC016286
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©2020. American Geophysical Union. All Rights Reserved.

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