02 Dec 2021

02 Dec 2021

Review status: this preprint is currently under review for the journal BG.

Diazotrophy as a key driver of the response of marine net primary productivity to climate change

Laurent Bopp1, Olivier Aumont2, Lester Kwiatkowski2, Corentin Clerc1, Léonard Dupont1, Christian Ethé3, Roland Séférian4, and Alessandro Tagliabue5 Laurent Bopp et al.
  • 1LMD/IPSL, Ecole Normale Supérieure/Université PSL, CNRS, Ecole Polytechnique, Sorbonne Université, Paris, France
  • 2LOCEAN/IPSL, Sorbonne Université, CNRS, IRD, MNHN, Paris, France
  • 3IPSL, Sorbonne Université, CNRS, Paris, France
  • 4CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 5School of Environmental Sciences, U. Liverpool, Liverpool, UK

Abstract. The impact of anthropogenic climate change on marine net primary production (NPP) is a reason for concern because changing NPP will have widespread consequences for marine ecosystems and their associated services. Projections by the current generation of Earth System Models have suggested decreases in global NPP in response to future climate change, albeit with very large uncertainties. Here, we make use of two versions of the Institut Pierre Simon Laplace Climate Model (IPSL-CM) that simulate divergent NPP responses to similar high-emission scenarios in the 21st century and identify nitrogen fixation as the main driver of these divergent NPP responses. Differences in the way N-fixation is parameterized in the marine biogeochemical component PISCES of the IPSL-CMs lead to N-fixation rates that are either stable or double over the course of the 21st century, resulting in decreasing or increasing global NPP, respectively. An evaluation of these 2 model versions does not help constrain future NPP projection uncertainties. However, the use of a more comprehensive version of PISCES, with variable nitrogen-to-phosphorus ratios as well as a revised parameterization of the temperature sensitivity of N-fixation, suggests only moderate changes of global-averaged N-fixation in the 21st century. This leads to decreasing global NPP, in line with the model-mean changes of a recent multi-model intercomparison. Lastly, despite contrasting trends in NPP, all our model versions simulate similar and significant reductions in planktonic biomass. This suggests that projected plankton biomass may be a much more robust indicator than NPP of the potential impact of anthropogenic climate change on marine ecosystems across model.

Laurent Bopp et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-320', Anonymous Referee #1, 16 Jan 2022
  • RC2: 'Comment on bg-2021-320', Anonymous Referee #2, 17 Jan 2022

Laurent Bopp et al.

Laurent Bopp et al.


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Short summary
The impact of anthropogenic climate change on the biological production of phytoplankton in the ocean is a cause for concern because its evolution could affect the response of marine ecosystems to climate change. Here, we identify biological N-fixation, and its response to future climate change, as a key process in shaping the future evolution of marine phytoplankton production. Our results show that further study of how this nitrogen fixation responds to environmental change is essential.