Significant nutrient consumption in the dark subsurface layer during a diatom bloom: a case study on Funka Bay, Hokkaido, Japan
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Published:2023-01-27
Issue:2
Volume:20
Page:421-438
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Umezawa Sachi, Tozawa Manami, Nosaka Yuichi, Nomura DaikiORCID, Onishi Hiroji, Abe Hiroto, Takatsu Tetsuya, Ooki AtsushiORCID
Abstract
Abstract. We conducted repetitive observations in Funka Bay,
Hokkaido, Japan, on 15 February, 4 and 15 March, and 14 April 2019. The
diatom spring bloom peaked on 4 March and started declining on 15 March.
Funka Bay winter water remained below 30 m depth, which was below the
surface mixed-layer and dark-layer depth (0.1 % of the surface photosynthetically active radiation, PAR, depth) on 4
and 15 March. In the subsurface layer at depths of 30–50 m, concentrations
of NO3-, PO43-, and Si(OH)4 decreased by half
between these dates, even in the dark. Incubation experiments using the
diatom Thalassiosira nordenskioeldii showed that this diatom could consume added nutrients in the dark at
substantial rates after pre-culturing to deplete nutrients. Incubation
experiments using natural seawater collected in the growing phase of the bloom on 8 March 2022 also showed that nutrient-depleted phytoplankton could consume
added nutrients in the dark. We excluded three physical
process – water mixing, diffusive transport, and subduction – as possible main
reasons for the decrease in nutrients in the subsurface layer. We conclude
that the nutrient reduction in the subsurface layer (30–50 m) between 4 and
15 March 2019 could be explained by nutrient consumption by diatoms in the dark in that
layer.
Funder
Japan Society for the Promotion of Science
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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