Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics
The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upst...
Published in: | Biogeosciences |
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Main Authors: | , , , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
European Geosciences Union (EGU)
2015
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Subjects: | |
Online Access: | https://archimer.ifremer.fr/doc/00256/36676/35276.pdf https://archimer.ifremer.fr/doc/00256/36676/71313.pdf https://doi.org/10.5194/bg-12-739-2015 https://archimer.ifremer.fr/doc/00256/36676/ |
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Open Polar |
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Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) |
op_collection_id |
ftarchimer |
language |
English |
description |
The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upstream high-nutrient, low-chlorophyll (HNLC), deep water (2500 m), reference station to compare with a shallow (500 m), strongly fertilised plateau station and continued the observations to a downstream, bathymetrically trapped recirculation of the Polar Front where eddies commonly form and persist for hundreds of kilometres into the Southern Ocean. Over the Kerguelen Plateau, mean particulate (1-53 mu m) Fe and Al concentrations (pFe = 13.4 nM, pAl = 25.2 nM) were more than 20-fold higher than at an offshore (lower-productivity) reference station (pFe = 0.53 nM, pAl = 0.83 nM). In comparison, over the plateau dissolved Fe levels were only elevated by a factor of similar to 2. Over the Kerguelen Plateau, ratios of pMn / pAl and pFe / pAl resemble basalt, likely originating from glacial/fluvial inputs into shallow coastal waters. In downstream, offshore deep-waters, higher pFe / pAl, and pMn / pAl ratios were observed, suggesting loss of lithogenic material accompanied by retention of pFe and pMn. Biological uptake of dissolved Fe and Mn and conversion into the biogenic particulate fraction or aggregation of particulate metals onto bioaggregates also increased these ratios further in surface waters as the bloom developed within the recirculation structure. While resuspension of shelf sediments is likely to be one of the important mechanisms of Fe fertilisation over the plateau, fluvial and glacial sources appear to be important to areas downstream of the island. Vertical profiles within an offshore recirculation feature associated with the Polar Front show pFe and pMn levels that were 6-fold and 3.5-fold lower, respectively, than over the plateau in surface waters, though still 3.6-fold and 1.7-fold higher respectively than the reference station. Within the recirculation feature, strong depletions of pFe and pMn were observed in the remnant winter water (temperature-minimum) layer near 175 m, with higher values above and below this depth. The correspondence between the pFe minima and the winter water temperature minima implies a seasonal cycle is involved in the supply of pFe into the fertilised region. This observed association is indicative of reduced supply in winter, which is counterintuitive if sediment resuspension and entrainment within the mixed layer is the primary fertilising mechanism to the downstream recirculation structure. Therefore, we hypothesise that lateral transport of pFe from shallow coastal waters is strong in spring, associated with snow melt and increased runoff due to rainfall, drawdown through summer and reduced supply in winter when snowfall and freezing conditions predominate in the Kerguelen region. |
format |
Article in Journal/Newspaper |
author |
Van Der Merwe, P. Bowie, A. R. Queroue, F. Armand, L. Blain, S. Chever, Fanny Davies, D. Dehairs, F. Planchon, F. Sarthou, G. Townsend, A. T. Trull, T. W. |
spellingShingle |
Van Der Merwe, P. Bowie, A. R. Queroue, F. Armand, L. Blain, S. Chever, Fanny Davies, D. Dehairs, F. Planchon, F. Sarthou, G. Townsend, A. T. Trull, T. W. Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
author_facet |
Van Der Merwe, P. Bowie, A. R. Queroue, F. Armand, L. Blain, S. Chever, Fanny Davies, D. Dehairs, F. Planchon, F. Sarthou, G. Townsend, A. T. Trull, T. W. |
author_sort |
Van Der Merwe, P. |
title |
Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
title_short |
Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
title_full |
Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
title_fullStr |
Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
title_full_unstemmed |
Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics |
title_sort |
sourcing the iron in the naturally fertilised bloom around the kerguelen plateau: particulate trace metal dynamics |
publisher |
European Geosciences Union (EGU) |
publishDate |
2015 |
url |
https://archimer.ifremer.fr/doc/00256/36676/35276.pdf https://archimer.ifremer.fr/doc/00256/36676/71313.pdf https://doi.org/10.5194/bg-12-739-2015 https://archimer.ifremer.fr/doc/00256/36676/ |
geographic |
Kerguelen Southern Ocean |
geographic_facet |
Kerguelen Southern Ocean |
genre |
Southern Ocean |
genre_facet |
Southern Ocean |
op_source |
Biogeosciences (1726-4170) (European Geosciences Union (EGU)), 2015-02-06 , Vol. 12 , N. 3 , P. 739-755 |
op_relation |
https://archimer.ifremer.fr/doc/00256/36676/35276.pdf https://archimer.ifremer.fr/doc/00256/36676/71313.pdf doi:10.5194/bg-12-739-2015 https://archimer.ifremer.fr/doc/00256/36676/ |
op_rights |
Author(s) 2015. CC Attribution 3.0 License. info:eu-repo/semantics/openAccess restricted use |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.5194/bg-12-739-2015 |
container_title |
Biogeosciences |
container_volume |
12 |
container_issue |
3 |
container_start_page |
739 |
op_container_end_page |
755 |
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1766207045350981632 |
spelling |
ftarchimer:oai:archimer.ifremer.fr:36676 2023-05-15T18:25:32+02:00 Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics Van Der Merwe, P. Bowie, A. R. Queroue, F. Armand, L. Blain, S. Chever, Fanny Davies, D. Dehairs, F. Planchon, F. Sarthou, G. Townsend, A. T. Trull, T. W. 2015-02-06 application/pdf https://archimer.ifremer.fr/doc/00256/36676/35276.pdf https://archimer.ifremer.fr/doc/00256/36676/71313.pdf https://doi.org/10.5194/bg-12-739-2015 https://archimer.ifremer.fr/doc/00256/36676/ eng eng European Geosciences Union (EGU) https://archimer.ifremer.fr/doc/00256/36676/35276.pdf https://archimer.ifremer.fr/doc/00256/36676/71313.pdf doi:10.5194/bg-12-739-2015 https://archimer.ifremer.fr/doc/00256/36676/ Author(s) 2015. CC Attribution 3.0 License. info:eu-repo/semantics/openAccess restricted use CC-BY Biogeosciences (1726-4170) (European Geosciences Union (EGU)), 2015-02-06 , Vol. 12 , N. 3 , P. 739-755 text Publication info:eu-repo/semantics/article 2015 ftarchimer https://doi.org/10.5194/bg-12-739-2015 2021-09-23T20:26:00Z The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upstream high-nutrient, low-chlorophyll (HNLC), deep water (2500 m), reference station to compare with a shallow (500 m), strongly fertilised plateau station and continued the observations to a downstream, bathymetrically trapped recirculation of the Polar Front where eddies commonly form and persist for hundreds of kilometres into the Southern Ocean. Over the Kerguelen Plateau, mean particulate (1-53 mu m) Fe and Al concentrations (pFe = 13.4 nM, pAl = 25.2 nM) were more than 20-fold higher than at an offshore (lower-productivity) reference station (pFe = 0.53 nM, pAl = 0.83 nM). In comparison, over the plateau dissolved Fe levels were only elevated by a factor of similar to 2. Over the Kerguelen Plateau, ratios of pMn / pAl and pFe / pAl resemble basalt, likely originating from glacial/fluvial inputs into shallow coastal waters. In downstream, offshore deep-waters, higher pFe / pAl, and pMn / pAl ratios were observed, suggesting loss of lithogenic material accompanied by retention of pFe and pMn. Biological uptake of dissolved Fe and Mn and conversion into the biogenic particulate fraction or aggregation of particulate metals onto bioaggregates also increased these ratios further in surface waters as the bloom developed within the recirculation structure. While resuspension of shelf sediments is likely to be one of the important mechanisms of Fe fertilisation over the plateau, fluvial and glacial sources appear to be important to areas downstream of the island. Vertical profiles within an offshore recirculation feature associated with the Polar Front show pFe and pMn levels that were 6-fold and 3.5-fold lower, respectively, than over the plateau in surface waters, though still 3.6-fold and 1.7-fold higher respectively than the reference station. Within the recirculation feature, strong depletions of pFe and pMn were observed in the remnant winter water (temperature-minimum) layer near 175 m, with higher values above and below this depth. The correspondence between the pFe minima and the winter water temperature minima implies a seasonal cycle is involved in the supply of pFe into the fertilised region. This observed association is indicative of reduced supply in winter, which is counterintuitive if sediment resuspension and entrainment within the mixed layer is the primary fertilising mechanism to the downstream recirculation structure. Therefore, we hypothesise that lateral transport of pFe from shallow coastal waters is strong in spring, associated with snow melt and increased runoff due to rainfall, drawdown through summer and reduced supply in winter when snowfall and freezing conditions predominate in the Kerguelen region. Article in Journal/Newspaper Southern Ocean Archimer (Archive Institutionnelle de l'Ifremer - Institut français de recherche pour l'exploitation de la mer) Kerguelen Southern Ocean Biogeosciences 12 3 739 755 |