Seminar: "Ocean Acidification Feedback: Decrease in Net Transfer Coefficient for Uptake of CO2 by the Global Ocean Due to Increase in Ocean Acidity" - Stephen Schwartz

Environmental Sciences Seminar:

"Ocean Acidification Feedback: Decrease in Net Transfer Coefficient for Uptake of CO2 by the Global Ocean Due to Increase in Ocean Acidity"

Stephen Schwartz
Adjunct Professor
Stony Brook University

Uptake of atmospheric CO2 by the global ocean, ~2.8 Pg yr--1 at present, reduces the increase of atmospheric CO2 due to anthropogenic emissions, thereby mitigating the effects of these emissions on Earth’s climate. Any secular change in net ocean drawdown would have important implications. This talk starts with a review of Earth’s CO2 budget over the Anthropocene. I then recap a simple three-compartment, concentration-driven model having only two independent, observationally determined parameters (3CCDM, Schwartz, Biogeosciences, 2025) and compare results with observations and other models. I introduce the net transfer coefficient from the atmosphere to the global ocean 𝑘aonet, the net transfer flux per amount of atmospheric CO2 in excess of preindustrial, or, equivalently, the fraction of excess atmospheric CO2 that is drawn down annually into the ocean. This net transfer coefficient provides a sensitive means of examining secular changes in ocean uptake. As determined from multiple observations and models, 𝑘aonet, is shown to exhibit systematic decrease over recent decades, about one-half percent per year. Using 3CCDM, the decrease is ascribed to decrease of CO2 solubility in the mixed-layer ocean resulting from ocean acidification. This decrease is calculated to have diminished the annual net drawdown of atmospheric CO2 between 1996 and 2022 by 0.5 Pg yr-1, with decrease in cumulative drawdown of 8 Pg or 3.7 ppm, equivalent to 1.7 year’s worth of atmospheric growth. I conclude with some thoughts about the use and usefulness of models.