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https://doi.org/10.5194/bg-2018-459
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2018-459
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 12 Nov 2018

Research article | 12 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Arctic (Svalbard Islands) Active and Exported Diatom Stocks and Cell Health Status

Susana Agustí1, Jeffrey W. Krause2,3, Israel A. Marquez2,3, Paul Wassmann4, Svein Kristiansen4, and Carlos M. Duarte1,5 Susana Agustí et al.
  • 1King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia
  • 2Dauphin Island Sea Lab, Dauphin Island, 36528-4603 United States
  • 3Department of Marine Sciences, University of South Alabama, Mobile, 36688-0002 United States
  • 4Department of Arctic and Marine Biology, UiT The Arctic University of Norway, 9037 Tromsø, Norway
  • 5Arctic Research Centre, Department of Biosscience, Aarrhus University, C.F. Mollers Alle 8, DK-8000 Arhus C, Denmark

Abstract. Diatoms tend to dominate the Arctic spring bloom, a key event in the ecosystem. Large sinking of diatoms is expected at the end of the bloom driven by deteriorated cell status associated to nutrients (silicon) depletion. However, there are few reports on the status of diatoms' health during Arctic blooms and its possible role on sedimentary fluxes. Here we quantify, using the Bottle-Net, Arctic diatom stocks below and above the photic layer and assess their cell health status. The communities were sampled around the Svalbard Islands and encompassed a broad diversity of conditions and bloom stages. About 1/4 (mean±SE 24.2 ± 6.7%) of the total water column (max. 415m) diatom stock was found below the photic layer, indicating significant sinking of diatoms in the area. The fraction of living diatom cells in the photic layer averaged 59.4 ± 6.3% but showed the highest percentages (72.0%) in stations supporting active blooms. In contrast, populations below the photic layer were dominated by dead cells (20.8 ± 4.9% living cells). The percentage of diatom’s stock found below the photic layer was negatively related to the percentage of living diatoms in the surface, indicating that healthy populations remained in the surface layer. An experiment on board in a tall (1.35m) sedimentation column confirmed that dead diatom cells from the Arctic community sink faster that living ones. Also, diatoms cell mortality increased in darkness, showing an averaged half life of 1.025 ± 0.075d−1. The results conform to a conceptual model where diatoms grow during the bloom until silicic acid stocks are depleted, and support a link between diatom cell health status and sedimentation fluxes in the Arctic. Healthy arctic phytoplankton communities remained at the photic layer, whereas dying communities exported a large fraction of the biomass to the aphotic zone, fuelling carbon sequestration and benthic ecosystems.

Susana Agustí et al.
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Susana Agustí et al.
Susana Agustí et al.
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Short summary
We found that 24 % of the total diatoms community in the Arctic water column (450 m depth) was located below the photic layer. Healthy diatoms communities in active spring-bloom stages remained in the photic layer. Dying diatom communities exported a large fraction of the biomass to the aphotic zone, fuelling carbon sequestration and benthic ecosystems in the Arctic. The results of the study conform to a conceptual model where diatoms grow during the bloom until silicic acid stocks are depleted.
We found that 24 % of the total diatoms community in the Arctic water column (450 m depth) was...
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