Preprints
https://doi.org/10.5194/bg-2022-45
https://doi.org/10.5194/bg-2022-45
 
24 Feb 2022
24 Feb 2022
Status: this preprint is currently under review for the journal BG.

First phytoplankton community assessment of the Kong Håkon VII Hav, Southern Ocean during austral autumn

Hanna Maria Kauko1, Philipp Assmy1, Ilka Peeken2, Magdalena Róźańska3, Józef M. Wiktor3, Gunnar Bratbak4, Asmita Singh5,6, Thomas J. Ryan-Keogh5, and Sebastien Moreau1 Hanna Maria Kauko et al.
  • 1Norwegian Polar Institute, Fram Centre, Tromsø, Norway
  • 2Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 3Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland
  • 4Department of Biological Sciences, University of Bergen, Bergen, Norway
  • 5Southern Ocean Carbon and Climate Observatory (SOCCO), Council for Scientific and Industrial Research (CSIR), Cape Town, South Africa
  • 6Department of Earth Sciences, Stellenbosch University, Stellenbosch, South Africa

Abstract. We studied phyto- and protozooplankton community composition based on light microscopy, flow cytometry and photosynthetic pigment data in the Atlantic sector of the Southern Ocean during March 2019 (early austral autumn). Sampling was focused on the area east of the prime meridian in the Kong Håkon VII Hav, including Astrid Ridge, Maud Rise and a south-north transect at 6° E. Phytoplankton community composition throughout the studied area was characterized by oceanic diatoms typical of the iron-deplete High-Nutrient Low-Chlorophyll (HNLC) Southern Ocean. Topography and wind-driven iron supply likely sustained blooms dominated by the centric diatom Chaetoceros dichaeta at Maud Rise and at a station north of the 6° E transect. For the remainder of the 6° E transect diatom composition was similar to the previously mentioned bloom stations but flagellates dominated in abundance suggesting a post-bloom situation and likely top-down control by krill on the bloom-forming diatoms. Among flagellates, species with haptophyte-type pigments were the dominating group. At Astrid Ridge, overall abundances were lower and pennate were more numerous than centric diatoms, but the community composition was nevertheless typical for HNLC areas. The observations described here show that C. dichaeta can form blooms beyond the background biomass level and fuels both carbon export and upper trophic levels also within HNLC areas. This study is the first thorough assessment of phytoplankton communities in this region and can be compared to other seasons in future studies.

Hanna Maria Kauko et al.

Status: open (until 29 May 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-45', Anonymous Referee #1, 20 Mar 2022 reply
    • AC1: 'Reply on RC1', Hanna Kauko, 18 May 2022 reply
  • RC2: 'Comment on bg-2022-45', Anonymous Referee #2, 24 May 2022 reply

Hanna Maria Kauko et al.

Hanna Maria Kauko et al.

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Short summary
This article studies phytoplankton (microscopic plants in the ocean capable of photosynthesis) in Kong Håkon VII Hav in the Southern Ocean. Different species play different roles in the ecosystem and it is therefore important to assess the species composition. We observed that phytoplankton blooms in this area are formed by large diatoms with strong silica armours, which can lead to high silica (and sometimes carbon) export to depth and be important prey for krill.
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