Projected increase in carbon dioxide drawdown and acidification in large estuaries under climate change

This article was originally published in Communications Earth & Environment. The version of record is available at: https://doi.org/10.1038/s43247-023-00733-5. © The Author(s) 2023 ; Most estuaries are substantial sources of carbon dioxide (CO2) to the atmosphere. The estimated estuarine CO2 degassing is about 17% of the total oceanic uptake, but the effect of rising atmospheric CO2 on estuarine carbon balance remains unclear. Here we use 3D hydrodynamic-biogeochemical models of a large eutrophic estuary and a box model of two generic, but contrasting estuaries to generalize how climate change affects estuarine carbonate chemistry and CO2 fluxes. We found that small estuaries with short flushing times remain a CO2 source to the atmosphere, but large estuaries with long flushing times may become a greater carbon sink and acidify. In particular, climate downscaling projections for Chesapeake Bay in the mid-21st century showed a near-doubling of CO2 uptake, a pH decline of 0.1–0.3, and >90% expansion of the acidic volume. Our findings suggest that large eutrophic estuaries will become carbon sinks and suffer from accelerated acidification in a changing climate. ; This study was funded by the U.S. National Oceanographic and Atmospheric Administration Ocean Acidification Program (NOAA‐OAP; Awards NA15NOS4780184 and NA18NOS4780179). WJC acknowledges the support by the National Science Foundation’s EPSCoR Program (grant #1757353) and the State of Delaware. This is UMCES Contribution Number 6286.