The Pinatubo CO2 pause suggests a rapidly testable path to multi-Gt mCDR - Preprint

[Geoengineering News]

https://www.researchsquare.com/article/rs-6960838/v1

Authors: Peter Fiekowsky, Alan K. Burnham

15 July 2025

https://doi.org/10.21203/rs.3.rs-6960838/v1

Abstract

After Pinatubo erupted in 1991, atmospheric CO2 levels stabilized during 1992–1993. Concentrations became ~ 2.25 ppm less than projected from contemporary emissions, corresponding to ~ 17.6 Gt of CO2 removed. CO2 did not return to projected levels in the following decades. Pinatubo ash fell into a downwelling eddy WSW of the volcano, which could explain the large, long-term CO2 removal. Of nine eruptions since 1500 that led to significant atmospheric cooling, three located near frequent downwelling mesoscale eddies resulted in notable CO2-level reductions. The six that were distant from downwelling eddies had no notable impact on atmospheric CO2. Therefore, CO2 reductions correlate with downwelling eddies rather than cooling. A CO2-pause hypothesis proposed by Sarmiento was that iron from the ashfall enabled a phytoplankton bloom that led to a large atmospheric CO2 removal. Local downwelling and converging eddies would have held high iron concentrations in place long enough to allow nitrogen-fixing bacteria to grow and provide the nitrate required. This nitrogen-fixing Ocean Iron Fertilization (N-OIF) process is a testable hypothesis which, if scaled, could provide a multi-Gt/y method for atmospheric CO2 removal.

Source: ResearchSquare