Preprints
https://doi.org/10.5194/bg-2022-68
https://doi.org/10.5194/bg-2022-68
 
17 Mar 2022
17 Mar 2022
Status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Physiological control on carbon isotope fractionation in marine phytoplankton

Karen M. Brandenburg1, Björn Rost2,3, Dedmer B. Van de Waal4, Mirja Hoins1,2, and Appy Sluijs1 Karen M. Brandenburg et al.
  • 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Princetonlaan 8a, 3584 CB Utrecht, the Netherlands
  • 2Department of Marine Biogeoscience, Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 3Faculty of Biology/Chemistry, University of Bremen, Leobener Strasse, 28359 Bremen, Germany
  • 4Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Droevendaalsesteeg 10, 6708 PB Wageningen, the Netherlands

Abstract. One of the great challenges in biogeochemical research over the past half a century has been to quantify and understand the mechanisms underlying stable carbon isotope fractionation (εp) in phytoplankton in response to changing pCO2. Partly, this interest is grounded in the use of fossil photosynthetic organism remains as a proxy for past atmospheric CO2 concentrations. Phytoplankton organic carbon is depleted in 13C compared to its source because of kinetic fractionation by the enzyme RubisCO during photosynthetic carbon fixation, as well as through physiological pathways upstream of RubisCO. Moreover, other factors such as nutrient limitation, variations in light regime as well as phytoplankton culturing systems and inorganic carbon manipulation approaches may confound the influence of CO2 on εp. Here, based on experimental data compiled from the literature, we assess which underlying physiological processes cause the observed differences in εp for various phytoplankton groups in response to C-demand/C-supply and test potential confounding factors. Culturing approaches and methods of carbonate chemistry manipulation were found to best explain the differences in εp between studies, although daylength was an important predictor for εp in haptophytes. Extrapolating results from culturing experiments to natural environments and for proxy applications therefore requires caution, and it should be carefully considered whether culture methods and experimental conditions are representative of natural environments.

Karen M. Brandenburg et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-68', Anonymous Referee #1, 06 Apr 2022
    • AC1: 'Reply on RC1', Karen Brandenburg, 21 Apr 2022
  • RC2: 'Comment on bg-2022-68', Anonymous Referee #2, 12 Apr 2022
    • AC2: 'Reply on RC2', Karen Brandenburg, 21 Apr 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-68', Anonymous Referee #1, 06 Apr 2022
    • AC1: 'Reply on RC1', Karen Brandenburg, 21 Apr 2022
  • RC2: 'Comment on bg-2022-68', Anonymous Referee #2, 12 Apr 2022
    • AC2: 'Reply on RC2', Karen Brandenburg, 21 Apr 2022

Karen M. Brandenburg et al.

Karen M. Brandenburg et al.

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Short summary
Reconstructions of past CO2 concentrations rely on proxy estimates, with one line of proxies relying on the CO2-dependence of stable carbon isotope fractionation in marine phytoplankton. Culturing experiments provide insight into which processes may impact this. We found, however, that the methods with which these culturing experiments are performed also influence 13C fractionation. Caution should therefore be taken when extrapolating results from these experiments to proxy applications.
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