Impact of Anthropogenic CO ₂ on the CaCO ₃ System in the Oceans

TLDR

Rising atmospheric CO₂ over the past two centuries has increased ocean CO₂ uptake, acidifying the oceans and altering calcium carbonate saturation states. The study estimates in situ CaCO₃ dissolution rates globally using total alkalinity and chlorofluorocarbon data, and discusses future impacts of anthropogenic CO₂ on CaCO₃ shell‑forming species. The authors derive dissolution rates from total alkalinity and chlorofluorocarbon measurements across the global oceans. Observed CaCO₃ dissolution rates range from 0.003 to 1.2 µmol kg⁻¹ yr⁻¹, with a global water‑column rate of ~0.5 ± 0.2 Pg CaCO₃‑C yr⁻¹, representing about 45–65 % of CaCO₃ export production.

Abstract

Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell-forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 +/- 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3.