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© 2018. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

Abstract

The island of South Georgia is situated in the iron (Fe)-depleted Antarctic Circumpolar Current of the Southern Ocean. Iron emanating from its shelf system fuels large phytoplankton blooms downstream of the island, but the actual supply mechanisms are unclear. To address this, we present an inventory of Fe, manganese (Mn), and aluminium (Al) in shelf sediments, pore waters, and the water column in the vicinity of South Georgia, alongside data on zooplankton-mediated Fe cycling processes, and provide estimates of the relative dissolved Fe (DFe) fluxes from these sources. Seafloor sediments, modified by authigenic Fe precipitation, were the main particulate Fe source to shelf bottom waters as indicated by the similar Fe / Mn and Fe / Al ratios for shelf sediments and suspended particles in the water column. Less than 1 % of the total particulate Fe pool was leachable surface-adsorbed (labile) Fe and therefore potentially available to organisms. Pore waters formed the primary DFe source to shelf bottom waters, supplying 0.1–44 µmol DFe m-2 d-1. However, we estimate that only 0.41±0.26 µmol DFe m-2 d-1 was transferred to the surface mixed layer by vertical diffusive and advective mixing. Other trace metal sources to surface waters included glacial flour released by melting glaciers and via zooplankton egestion and excretion processes. On average 6.5±8.2 µmol m-2 d-1 of labile particulate Fe was supplied to the surface mixed layer via faecal pellets formed by Antarctic krill (Euphausia superba), with a further 1.1±2.2 µmol DFe m-2 d-1 released directly by the krill. The faecal pellets released by krill included seafloor-derived lithogenic and authigenic material and settled algal debris, in addition to freshly ingested suspended phytoplankton cells.

The Fe requirement of the phytoplankton blooms 1250 km downstream of South Georgia was estimated as 0.33±0.11 µmol m-2 d-1, with the DFe supply by horizontal/vertical mixing, deep winter mixing, and aeolian dust estimated as 0.12 µmol m-2 d-1. We hypothesize that a substantial contribution of DFe was provided through recycling of biogenically stored Fe following luxury Fe uptake by phytoplankton on the Fe-rich shelf. This process would allow Fe to be retained in the surface mixed layer of waters downstream of South Georgia through continuous recycling and biological uptake, supplying the large downstream phytoplankton blooms.

Details

Title
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean
Author
Schlosser, Christian 1   VIAFID ORCID Logo  ; Schmidt, Katrin 2 ; Aquilina, Alfred 3 ; Homoky, William B 4 ; Castrillejo, Maxi 5 ; Mills, Rachel A 3   VIAFID ORCID Logo  ; Patey, Matthew D 3   VIAFID ORCID Logo  ; Fielding, Sophie 6 ; Atkinson, Angus 7 ; Achterberg, Eric P 1 

 Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UK; GEOMAR Helmholtz Centre for Ocean Research, Wischhofstr. 1–3, 24148 Kiel, Germany 
 British Antarctic Survey, CB3 0ET Cambridge, UK; School of Geography, Earth and Environmental Sciences, University of Plymouth, PL4 8AA Plymouth, UK 
 Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UK 
 Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UK; Department of Earth Sciences, University of Oxford, OX1 3AN Oxford, UK 
 Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UK; Institut de Ciència i Tecnologia Ambientals & Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain 
 British Antarctic Survey, CB3 0ET Cambridge, UK 
 British Antarctic Survey, CB3 0ET Cambridge, UK; Plymouth Marine Laboratory, Prospect Place, The Hoe, PL1 3DH Plymouth, UK 
Pages
4973-4993
Publication year
2018
Publication date
2018
Publisher
Copernicus GmbH
ISSN
17264170
e-ISSN
17264189
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
2091072893
Copyright
© 2018. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.