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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-16
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-16
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 27 Jan 2020

Submitted as: research article | 27 Jan 2020

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This preprint is currently under review for the journal BG.

Twenty-first century ocean warming, acidification, deoxygenation, and upper ocean nutrient decline from CMIP6 model projections

Lester Kwiatkowski1, Olivier Torres2, Laurent Bopp2, Olivier Aumont1, Matthew Chamberlain3, James Christian4, John P. Dunne5, Marion Gehlen6, Tatiana Ilyina7, Jasmin G. John5, Andrew Lenton3, Hongmei Li7, Nicole S. Lovenduski8, James C. Orr6, Julien Palmieri9, Jörg Schwinger10, Roland Séférian11, Charles A. Stock5, Alessandro Tagliabue12, Yohei Takano7, Jerry Tjiputra10, Katsuya Toyama13, Hiroyuki Tsujino13, Michio Watanabe14, Akitomo Yamamoto14, Andrew Yool9, and Tilo Ziehn3 Lester Kwiatkowski et al.
  • 1LOCEAN Laboratory, Sorbonne Université-CNRS-IRD-MNHN, Paris, 75005, France
  • 2LMD-IPSL, CNRS, Ecole Normale Supérieure/PSL Res. Univ, Ecole Polytechnique, Sorbonne Université, Paris, 75005, France
  • 3CSIRO Oceans and Atmosphere, Hobart, TAS 7000, Australia
  • 4Canadian Centre for Climate Modelling and Analysis, Victoria, BC, Canada
  • 5NOAA Geophysical Fluid Dynamics Laboratory Princeton, New Jersey, USA
  • 6Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL, CEA-CNRS-UVSQ, Université Paris Saclay, Gif-sur-Yvette, France
  • 7Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg, Germany
  • 8Department of Atmospheric and Oceanic Sciences and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado, USA
  • 9National Oceanography Centre, European Way, Southampton, SO14 3ZH, UK
  • 10NORCE Climate, Bjerknes Centre for Climate Research, Bergen, Norway
  • 11CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 12School of Environmental Sciences, University of Liverpool, UK
  • 13Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan
  • 14Research Center for Environmental Modeling and Application, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan

Abstract. Anthropogenic climate change leads to ocean warming, acidification, deoxygenation and reductions in near-surface nutrient concentrations, all of which are expected to affect marine ecosystems. Here we assess projections of these drivers of environmental change over the twenty-first century from Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) that were forced under the CMIP6 Shared Socioeconomic Pathways (SSPs). Projections are compared to those from the previous generation (CMIP5) forced under the Representative Concentration Pathways (RCPs). 10 CMIP5 and 13 CMIP6 models are used in the two multi-model ensembles. Under the high-emission scenario SSP5–8.5, the model mean change (2080–2099 mean values relative to 1870–1899) in sea surface temperature, surface pH, subsurface (100–600 m) oxygen concentration and euphotic (0–100 m) nitrate concentration is +3.48 ± 0.78 °C, −0.44 ± 0.005, −13.27 ± 5.28 mmol m−3 and −1.07 ± 0.45 mmol m−3, respectively. Under the low-emission, high-mitigation scenario SSP1–2.6, the corresponding changes are +1.42 ± 0.32 °C, −0.16 ± 0.002, −6.36 ± 2.92 mmol m−3 and −0.53 ± 0.23 mmol m−3. Projected exposure of the marine ecosystem to these drivers of ocean change depends largely on the extent of future emissions, consistent with previous studies. The Earth system models in CMIP6 generally project greater surface warming, acidification, deoxygenation and euphotic nitrate reductions than those from CMIP5 under comparable radiative forcing, with no reduction in inter-model uncertainties. Under the high-emission CMIP5 scenario RCP8.5, the corresponding changes in sea surface temperature, surface pH, subsurface oxygen and euphotic nitrate concentration are +3.04 ± 0.62 °C, −0.38 ± 0.005, −9.51 ± 2.13 mmol m−3 and −0.66 ± 0.49 mmol m−3, respectively. The greater surface acidification in CMIP6 is primarily a consequence of the SSPs having higher associated atmospheric CO2 concentrations than their RCP analogues. The increased projected warming results from a general increase in the climate sensitivity of CMIP6 models relative to those of CMIP5. This enhanced warming results in greater increases in upper ocean stratification in CMIP6 projections, which contributes to greater reductions in euphotic nitrate and subsurface oxygen ventilation.

Lester Kwiatkowski et al.

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Lester Kwiatkowski et al.

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Short summary
We assess 21st century projections of marine biogeochemistry in the Coupled Model Intercomparison Project Phase 6 Earth system models. These models represent our most up-to-date understanding of future climate change. The Earth system models generally project greater surface-ocean warming, acidification, subsurface deoxygenation and euphotic nitrate reductions than previous generation models. This has major implications for the impact of anthropogenic climate change on marine ecosystems.
We assess 21st century projections of marine biogeochemistry in the Coupled Model...
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