Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean
<p>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...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2018-08-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/4973/2018/bg-15-4973-2018.pdf |
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doaj-5a5747e922a1468c80ec9f8bfb9d7ca8 |
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Article |
| collection |
DOAJ |
| language |
English |
| format |
Article |
| sources |
DOAJ |
| author |
C. Schlosser C. Schlosser K. Schmidt K. Schmidt A. Aquilina W. B. Homoky W. B. Homoky M. Castrillejo M. Castrillejo R. A. Mills M. D. Patey S. Fielding A. Atkinson A. Atkinson E. P. Achterberg E. P. Achterberg |
| spellingShingle |
C. Schlosser C. Schlosser K. Schmidt K. Schmidt A. Aquilina W. B. Homoky W. B. Homoky M. Castrillejo M. Castrillejo R. A. Mills M. D. Patey S. Fielding A. Atkinson A. Atkinson E. P. Achterberg E. P. Achterberg Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean Biogeosciences |
| author_facet |
C. Schlosser C. Schlosser K. Schmidt K. Schmidt A. Aquilina W. B. Homoky W. B. Homoky M. Castrillejo M. Castrillejo R. A. Mills M. D. Patey S. Fielding A. Atkinson A. Atkinson E. P. Achterberg E. P. Achterberg |
| author_sort |
C. Schlosser |
| title |
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean |
| title_short |
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean |
| title_full |
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean |
| title_fullStr |
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean |
| title_full_unstemmed |
Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean |
| title_sort |
mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off south georgia, southern ocean |
| publisher |
Copernicus Publications |
| series |
Biogeosciences |
| issn |
1726-4170 1726-4189 |
| publishDate |
2018-08-01 |
| description |
<p>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<sup>−2</sup> d<sup>−1</sup>.
However, we estimate that only 0.41±0.26 µmol DFe m<sup>−2</sup> d<sup>−1</sup> 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<sup>−2</sup> d<sup>−1</sup> of labile particulate Fe was supplied to the surface
mixed layer via faecal pellets formed by Antarctic krill (<i>Euphausia
superba</i>), with a further 1.1±2.2 µmol DFe m<sup>−2</sup> d<sup>−1</sup>
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.</p><p>The Fe requirement of the phytoplankton blooms ∼ 1250 km
downstream of South Georgia was estimated as 0.33±0.11 µmol m<sup>−2</sup> d<sup>−1</sup>, with the DFe supply by horizontal/vertical mixing, deep
winter mixing, and aeolian dust estimated as ∼ 0.12 µmol m<sup>−2</sup> d<sup>−1</sup>. 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.</p> |
| url |
https://www.biogeosciences.net/15/4973/2018/bg-15-4973-2018.pdf |
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doaj-5a5747e922a1468c80ec9f8bfb9d7ca82020-11-25T00:07:19ZengCopernicus PublicationsBiogeosciences1726-41701726-41892018-08-01154973499310.5194/bg-15-4973-2018Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern OceanC. Schlosser0C. Schlosser1K. Schmidt2K. Schmidt3A. Aquilina4W. B. Homoky5W. B. Homoky6M. Castrillejo7M. Castrillejo8R. A. Mills9M. D. Patey10S. Fielding11A. Atkinson12A. Atkinson13E. P. Achterberg14E. P. Achterberg15Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKGEOMAR Helmholtz Centre for Ocean Research, Wischhofstr. 1–3, 24148 Kiel, GermanyBritish Antarctic Survey, CB3 0ET Cambridge, UKSchool of Geography, Earth and Environmental Sciences, University of Plymouth, PL4 8AA Plymouth, UKOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKDepartment of Earth Sciences, University of Oxford, OX1 3AN Oxford, UKOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKInstitut de Ciència i Tecnologia Ambientals & Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, SpainOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKBritish Antarctic Survey, CB3 0ET Cambridge, UKBritish Antarctic Survey, CB3 0ET Cambridge, UKPlymouth Marine Laboratory, Prospect Place, The Hoe, PL1 3DH Plymouth, UKOcean and Earth Science, National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UKGEOMAR Helmholtz Centre for Ocean Research, Wischhofstr. 1–3, 24148 Kiel, Germany<p>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<sup>−2</sup> d<sup>−1</sup>. However, we estimate that only 0.41±0.26 µmol DFe m<sup>−2</sup> d<sup>−1</sup> 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<sup>−2</sup> d<sup>−1</sup> of labile particulate Fe was supplied to the surface mixed layer via faecal pellets formed by Antarctic krill (<i>Euphausia superba</i>), with a further 1.1±2.2 µmol DFe m<sup>−2</sup> d<sup>−1</sup> 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.</p><p>The Fe requirement of the phytoplankton blooms ∼ 1250 km downstream of South Georgia was estimated as 0.33±0.11 µmol m<sup>−2</sup> d<sup>−1</sup>, with the DFe supply by horizontal/vertical mixing, deep winter mixing, and aeolian dust estimated as ∼ 0.12 µmol m<sup>−2</sup> d<sup>−1</sup>. 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.</p>https://www.biogeosciences.net/15/4973/2018/bg-15-4973-2018.pdf |