08 Apr 2022
08 Apr 2022
Status: this preprint is currently under review for the journal ESD.

Contrasting projection of the ENSO-driven CO2 flux variability in the Equatorial Pacific under high warming scenario

Pradeebane Vaittinada Ayar1, Jerry Tjiputra1, Laurent Bopp2, Jim R. Christian3, Tatiana Ilyina4, John P. Krasting5, Roland Séférian6, Hiroyuki Tsujino7, Michio Watanabe8, and Andrew Yool9 Pradeebane Vaittinada Ayar et al.
  • 1NORCE Norwegian Research Centre AS, Bjerknes Centre for Climate Research, Bergen, Norway
  • 2LMD-IPSL, Ecole Normale Supérieure / Université PSL, CNRS, Ecole Polytechnique, Sorbonne Université, Paris, PSL University, Paris, France
  • 3Canadian Centre for Climate Modelling and Analysis, Victoria, BC, CA
  • 4Max Planck Institute for Meteorology, Hamburg, Germany
  • 5NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey 08540, USA
  • 6CNRM, Université de Toulouse, Météo-France, CNRS, Toulouse, France
  • 7JMA Meteorological Research Institute, Tsukuba, Ibaraki, Japan
  • 8Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 3173-25, Showa-machi, Kanazawa-ku, Yokohama, Kanagawa, 236-0001, Japan
  • 9National Oceanography Centre, Southampton, UK

Abstract. The El Niño Southern Oscillation (ENSO) widely modulates the global carbon cycle, in particular, by altering the net uptake of carbon in the tropical ocean. Indeed, over the tropics less carbon is released by oceans during El Niño while it is the opposite for La Niña. Here, the skill of Earth System Models (ESM) from the latest Coupled Model Intercomparison Project (CMIP6) to simulate the observed tropical Pacific CO2 flux variability in response to ENSO is assessed. The temporal amplitude and spatial extent of CO2 flux anomalies vary considerably among models, while the surface temperature signals of El Niño and La Niña phases are generally well represented. Under historical conditions followed by the high warming Shared Socio-economic Pathway (SSP5-8.5) scenarios, about half the ESMs simulate a reversal in ENSO-CO2 flux relationship. This gradual shift, which occurs as early as the first half of the 21st century, is associated with a high CO2-induced increase in Revelle factor that leads to stronger sensitivity of partial pressure of CO2 (pCO2) to changes in surface temperature between ENSO phases. At the same time, uptake of anthropogenic CO2 substantially increases upper ocean dissolved inorganic carbon (DIC) concentrations, reducing its vertical gradient in the thermocline, and weakening the ENSO-modulated surface DIC variability. The response of ENSO-CO2 flux relationship to future climate change is sensitive to the contemporary mean state of the carbonate ion concentration in the tropics. Models that simulate shift in ENSO-CO2 flux relationship simulate positive bias in surface carbonate concentration.

Pradeebane Vaittinada Ayar et al.

Status: open (until 27 May 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2022-12', Anonymous Referee #1, 17 May 2022 reply
  • RC2: 'Comment on esd-2022-12', Anonymous Referee #2, 23 May 2022 reply

Pradeebane Vaittinada Ayar et al.

Pradeebane Vaittinada Ayar et al.


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Short summary
The El Niño Southern Oscillation is the main driver for the natural variability of global atmospheric CO2. It modulates the CO2 fluxes in the tropical Pacific with anomalously CO2 influx during El Niño and outflux during La Niña. Climate projections under the business-as-usual scenario show a reversal of this behaviour is projected by half of Earth System Models. Changes in Revelle factor and subsurface distribution of dissolved Inorganic carbon are the two leading factors for this reversal.