- 1LMD/IPSL, Ecole Normale Supérieure/Université PSL, CNRS, Ecole Polytechnique, Sorbonne Université; Paris, 75005, France. (alban.planchat@unibe.ch)
- 2Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland.
- 3Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland.
- 4LOCEAN/IPSL, Sorbonne Université, CNRS, IRD, MNHN; Paris, 75005, France.
As the oceans warm and acidify, the calcification of coral reefs declines, with net calcium carbonate dissolution projected even under moderate emissions scenarios. The impact of this on the global carbon cycle is however yet to be accounted for. We use a synthesis of the sensitivity of coral reef calcification to climate change, alongside reef distribution products to estimate alkalinity and dissolved inorganic carbon fluxes resulting from reductions in reef calcification. Using the global ocean biogeochemical model NEMO-PISCES, we simulate the impact of these fluxes on ocean carbon uptake under different emissions scenarios, accounting for uncertainty in present-day calcification rates.
Reductions in global coral reef carbonate production could enhance the ocean anthropogenic carbon sink by 0.34 PgC yr-1by mid-century (0.13 PgC yr-1 median estimate) with cumulative ocean carbon uptake up to 110 PgC greater by 2300 (46 PgC median estimate). Under medium to high emissions scenarios, two critical aspects emerge: (i) the full potential for coral reef degradation to affect carbon fluxes is reached within decades, and (ii) air-sea carbon fluxes remain substantial for centuries, due to the imbalance between carbon and alkalinity sinks/sources for the global ocean.
Accounting for the coral reef feedback into Earth system models could revise upward remaining carbon budget estimates, increasing the likelihood of achieving net-zero emissions without relying on negative emissions. The coral reef feedback could have a 21st-century impact comparable in magnitude to boreal forest dieback, though opposite in sign. This underscores a critical paradox: conserving calcifying organisms, such as coral reefs, may counteract a natural mechanism for mitigating climate change, but at the cost of protecting vital biodiversity. This challenges the "all-carbon" framework often used to address environmental issues, highlighting the complex trade-offs between carbon cycle regulation and biodiversity conservation.
How to cite: Planchat, A., Kwiatkowski, L., Pyolle, M., Laufkötter, C., and Bopp, L.: Declining coral calcification to enhance twenty-first century ocean carbon uptake by gigatons, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10326, https://doi.org/10.5194/egusphere-egu25-10326, 2025.
