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https://doi.org/10.5194/bg-2019-343
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-343
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 30 Aug 2019

Submitted as: research article | 30 Aug 2019

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

The Arctic picoeukaryote Micromonas pusilla benefits from Ocean Acidification under constant and dynamic light

Emily White1, Clara J. M. Hoppe1, and Björn Rost1,2 Emily White et al.
  • 1Alfred-Wegener-Institut–Helmholtz-Zentrum für Polar-und Meeresforschung, Bremerhaven, 27570, Germany
  • 2Universität Bremen, FB2, Leobener Strasse, 28359 Bremen, Germany

Abstract. Compared to the rest of the globe, the Arctic Ocean is affected disproportionately by climate change. Despite these fast environmental changes, we currently know little about the effects of ocean acidification (OA) on marine key species in this area. Moreover, the existing studies typically test the effects of OA under constant, hence artificial light fields. In this study, the abundant Arctic picoeukaryote Micromonas pusilla was acclimated to current (400 μatm) and future (1000 μatm) pCO2 levels under a constant as well as dynamic light, simulating natural light fields as experienced in the upper mixed layer. To describe and understand the responses to these drivers, growth, particulate organic carbon (POC) production, elemental composition, photophysiology and reactive oxygen species (ROS) production were analysed. M. pusilla was able to benefit from OA on various scales, ranging from an increase in growth rates to enhanced photosynthetic capacity, irrespective of the light regime. These beneficial effects were, however, not reflected in the POC production rates, which can be explained by energy partitioning towards cell division rather than biomass build-up. In the dynamic light regime, M. pusilla was able to optimise its photophysiology for effective light usage during both low and high light periods. This effective photoacclimation, which was achieved by modifications to photosystem II (PSII), imposed high metabolic costs leading to a reduction in growth and POC production rates when compared to constant light. There were no significant interactions observed between dynamic light and OA, indicating that M. pusilla was able maintain effective photoacclimation without increased photoinactivation under high pCO2. Based on these findings, physiologically plastic M. pusilla may exhibit a robust positive response to future Arctic Ocean conditions.

Emily White et al.
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The Arctic picoeukaryote Micromonas pusilla was acclimated to two pCO2 levels under a constant as well as dynamic light, simulating natural light fields. M. pusilla was able to benefit from ocean acidification with an increase in growth rate, irrespective of the light field. In dynamic light M. pusilla optimised its photophysiology for effective light usage during both low and high light periods. This highlights M. pusilla may exhibit a robust positive response to future Arctic Ocean conditions.
The Arctic picoeukaryote Micromonas pusilla was acclimated to two pCO2 levels under a constant...
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