| Abstrakt: |
The ocean carbon reservoir controls atmospheric carbon dioxide (CO2) on millennial timescales. Radiocarbon (14C) anomalies in eastern North Pacific sediments suggest a significant release of geologic 14C‐free carbon at the end of the last ice age but without evidence of ocean acidification. Using inverse carbon cycle modeling optimized with reconstructed atmospheric CO2 and 14C/C, we develop first‐order constraints on geologic carbon and alkalinity release over the last 17.5 thousand years. We construct scenarios allowing the release of 850–2,400 Pg C, with a maximum release rate of 1.3 Pg C yr−1, all of which require an approximate equimolar alkalinity release. These neutralized carbon addition scenarios have minimal impacts on the simulated marine carbon cycle and atmospheric CO2, thereby demonstrating safe and effective ocean carbon storage. This deglacial phenomenon could serve as a natural analog to the successful implementation of gigaton‐scale ocean alkalinity enhancement, a promising marine carbon dioxide removal method. Plain Language Summary: The ocean is the largest carbon reservoir on Earth's surface and, as such, it controls the concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere over long time periods. When CO2 was rising at the end of the last ice age, marine sediment evidence indicates a regional carbon release into the ocean, due to a distinct carbon isotope fingerprint left behind. Using a carbon cycle model and atmospheric data, we simulated different geologic carbon addition scenarios since the last ice age. We find that substantial carbon addition to the ocean could have occurred (up to 1.3 billion tons per year) without causing significant changes to the carbon cycle, but only if the carbon is neutralized by alkalinity in an approximate 1:1 ratio. This neutralized release is similar to an approach of carbon removal called ocean alkalinity enhancement (OAE), which aims to reduce atmospheric CO2 as a potential solution for climate change. These findings suggest that neutralized carbon addition—in the form of "neutralized" bicarbonate ion HCO3− $\left({\text{HCO}}_{3}^{-}\right)$ instead of "acidic" CO2—could explain the low levels of radiocarbon during the last deglaciation and shows that large‐scale OAE is feasible without causing major changes to the marine carbon cycle. Key Points: Observed deglacial changes in atmospheric CO2 and 14C/C allow for up to 2,396 Pg of neutralized geologic carbon (i.e., bicarbonate) releaseThe global carbon cycle is essentially "blind" to neutralized carbon release, only constrained by 14C budgetThis gigaton‐scale neutralized carbon release may be a natural analog to the marine CO2 removal method of ocean alkalinity enhancement [ABSTRACT FROM AUTHOR] |
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