Preprints
https://doi.org/10.5194/bg-2021-357
https://doi.org/10.5194/bg-2021-357
 
06 Jan 2022
06 Jan 2022
Status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Nutrient consumption by diatoms in the dark subsurface layer of Funka Bay, Hokkaido, Japan

Sachi Umezawa1, Manami Tozawa1, Yuichi Nosaka2, Daiki Nomura3,4,1, Hiroji Onishi1, Hiroto Abe1, Tetsuya Takatsu1, and Atsushi Ooki1,4 Sachi Umezawa et al.
  • 1Graduate School of Fisheries Sciences/Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, 041-8611, Japan
  • 2Tokai University, Department of Marine Biology and Sciences, 5-1-1, Minamisawa, Minami-ku, Sapporo, Hokkaido, 005-8601, Japan
  • 3Field Science Center for Northern Biosphere, Hokkaido University, 3-1-1 Minato Cho, Hakodate, Hokkaido 0418611, Japan
  • 4Arctic Research Center, Hokkaido University, Kita-21 Nishi-11 Kita-ku, Sapporo, Hokkaido, 001-0021, Japan

Abstract. We conducted time-series observations in Funka Bay, Hokkaido, Japan, from 15 February to 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-zone depths on both dates. At depths of 30–50 m, concentrations of NO3, PO43–, and Si(OH)4 decreased by half between these dates even in darkness. Incubation experiments using the diatom Thalassiosira nordenskioeldii showed that this diatom could consume nutrients in darkness at substantial rates. We conclude that the nutrient reduction in the subsurface layer (30–50 m) could be explained by dark consumption by diatoms that had been growing in the surface waters and then sank to the subsurface layer. We believe that this is the first study to present observational evidence for the consumption of the main nutrients by diatoms in the dark subsurface layer during the spring bloom. Nutrient consumption in this layer might have a substantial influence on the primary production during and after the spring bloom.

Sachi Umezawa et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-357', Anonymous Referee #1, 08 Jan 2022
    • AC1: 'Reply on RC1', Atsushi Ooki, 15 Feb 2022
    • AC2: 'Reply on RC1', Atsushi Ooki, 11 Mar 2022
  • RC2: 'Comment on bg-2021-357', Anonymous Referee #2, 14 Feb 2022
    • AC3: 'Reply on RC2', Atsushi Ooki, 11 Mar 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-357', Anonymous Referee #1, 08 Jan 2022
    • AC1: 'Reply on RC1', Atsushi Ooki, 15 Feb 2022
    • AC2: 'Reply on RC1', Atsushi Ooki, 11 Mar 2022
  • RC2: 'Comment on bg-2021-357', Anonymous Referee #2, 14 Feb 2022
    • AC3: 'Reply on RC2', Atsushi Ooki, 11 Mar 2022

Sachi Umezawa et al.

Sachi Umezawa et al.

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Short summary
We conducted time-series observations in Funka Bay, Japan, during the spring bloom 2019. We found reductions in nutrient concentrations in the dark subsurface layer in the bloom. Incubation experiment confirmed that diatom could consume nutrients at substantial rate even in darkness. We concluded that nutrient reduction was caused by dark consumption by diatoms that had grown in the surface euphotic layer and then sank to the dark subsurface layer.
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