Anthropogenically Stimulated Carbonate Dissolution in the Global Shelf Seafloor Is Potentially an Important and Fast Climate Feedback

Abstract Carbonate mineral production and dissolution regulate atmospheric carbon dioxide (CO 2 ) concentrations via modulation of the ocean alkalinity content. The anthropogenic rise in atmospheric CO 2 reduces calcification rates and enhances calcium carbonate dissolution, which increases ocean alkalinity, counteracts acidification, and stimulates ocean CO 2 uptake. However, carbonate dissolution takes place primarily in the deep ocean, so this feedback is slow, maintaining ocean CO 2 uptake over millennial timescales. Here, we present evidence that seawater alkalinity on the continental shelf is increasing on annual‐decadal timescales, at a rate that is orders of magnitude faster than the deep ocean feedback. Biogeochemical model analyses suggest this fast feedback results from calcium carbonate dissolution in the shelf seafloor driven by increasing atmospheric CO 2 concentrations. Extrapolating these results to the global continental shelf suggests that shelf carbonate dissolution has been accelerating since the 1800s and may account for up to 10% of the missing ∼0.3 Pg C yr −1 in ocean model carbon budgets.