Has Seasonal Ocean Calcification Been Overlooked as a Cause of the Increasing Keeling Curve? A Thermal Acidifying Calcification Hypothesis
Year: 2025
Type: article
Abstract: The Keeling Curve documents a steady rise in partial atmospheric pressure of CO₂ (pCO2), conventionally attributed to fossil fuel emissions. Here, we propose an alternative cause, the thermal acidifying-calcification (TAC) hypothesis, principles of physical chemistry showing that warmingwill induce calcification in surface seawater, driving seasonal and longer-term increases in atmospheric pCO2. Using thermodynamic modeling and oceanographic data, we estimate that precipitation of ~10 μmol of of CaCO₃ per kg of surface seawater annually could release sufficient CO₂ to equilibrate locally with the recent 2 ppmv annual rise in atmospheric pCO2. Seasonal pH and pCO2 variations at marine stations (e.g., ALOHA, Hawaii) support this mechanism, challenging the dominant terrestrial photosynthesis- respiration explanation for Keeling oscillations. The TAC process can also explain the decreasing trend in 13CO2 in air because of dilution by the same processes that are driving the longer-term increase in atmospheric pCO2. To test this hypothesis, we recommend the following program: 1. field validation of CaCO₃ deposition rates, 2. measures of the CO2 flux and 3. isotopic analysis to test this alternative carbon cycle driver with measures to be taken both in the northern Pacific and in the southern hemisphere on a transect past the Great Barrier Reef.
Author: Ivan R Kennedy
Institution: The University of Sydney
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W7084071394
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