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https://doi.org/10.5194/bg-2019-488
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-488
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  31 Jan 2020

31 Jan 2020

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This preprint is currently under review for the journal BG.

Factors controlling the competition between Phaeocystis and diatoms in the Southern Ocean

Cara Nissen and Meike Vogt Cara Nissen and Meike Vogt
  • Institute for Biogeochemistry and Pollutant Dynamics, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland

Abstract. The high-latitude Southern Ocean phytoplankton community is shaped by the competition between Phaeocystis and silicifying diatoms, with the relative abundance of these two groups controlling primary and export production, the production of dimethylsulfide, the ratio of silicic acid and nitrate available in the water column, and the structure of the food web. Here, we investigate this competition using a regional physical-biogeochemical-ecological model (ROMS-BEC) configured at eddy-permitting resolution for the Southern Ocean south of 35° S. We extended ROMS-BEC by an explicit parameterization of Phaeocystis colonies, so that the model, together with the previous addition of an explicit coccolithophore type, now includes all biogeochemically relevant Southern Ocean phytoplankton types. We find that Phaeocystis contribute 46 % and 40 % to annual NPP and POC export south of 60° S, respectively, making them an important contributor to high-latitude carbon cycling. In our simulation, the relative importance of Phaeocystis and diatoms is mainly controlled by the temporal variability in temperature and iron availability. The higher light sensitivity of Phaeocystis at low irradiances promotes the succession from Phaeocystis to diatoms in more coastal areas, such as the Ross Sea. Still, differences in the biomass loss rates, such as aggregation or grazing by zooplankton, need to be considered to explain the simulated seasonal biomass evolution.

Cara Nissen and Meike Vogt

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Cara Nissen and Meike Vogt

Cara Nissen and Meike Vogt

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Latest update: 27 Sep 2020
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Short summary
Using a regional Southern Ocean ecosystem model, we find that the relative importance of Phaeocystis and diatoms at high latitudes is controlled by iron and temperature variability, with light levels controlling the seasonal succession in coastal areas. Yet, biomass losses via aggregation and grazing matter as well. We show that the seasonal variability of Phaeocystis and diatoms impacts the seasonality of carbon export fluxes, with ramifications for nutrient cycling and food web dynamics.
Using a regional Southern Ocean ecosystem model, we find that the relative importance of...
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