Assessing the photochemical production of carbon dioxide in the ocean


OCCI Funded Project: 2006


Ultimately, the ocean’s ability to act as a sink for anthropogenically produced carbon dioxide (CO2) is governed by the equilibrium between atmospheric and oceanic concentrations. Predicting the ocean’s ability to continue to act as a sink for atmospheric CO2 relies on a clear understanding of the sources and sinks of dissolved inorganic carbon. Recent evidence suggests that a major unconstrained source of CO2 in the upper ocean is the photochemical destruction of dissolved organic carbon (DOC). Initial estimates suggest that CO2 production rates from DOC may be of the same magnitude or larger than the anthropogenic uptake suggesting large ramifications for oceanic CO2 concentrations. Through the proposed work, we hope to develop an improved, quantitative assessment of the magnitude and mechanisms driving upper-ocean CO2 photo-production.

Fundamental methodological gaps have to date prohibited us from assessing the importance of CO2 photo-production in the global carbon cycle. Our goal in this project is to refine a new pool isotope exchange (PIE) method for measuring extremely small in situ CO2 concentration changes. In the marine environment, organic and inorganic carbon have a fairly consistent isotopic ratio of 98.9%  13C to 1.1% 13C. We will leverage this by effectively replacing all of the 12CO2 with 13CO2 and monitoring the evolution of 12CO2 from dissolved organic material with the standard isotopic ratio. This work will provide the foundation for global modeling efforts and will provide a more realistic assessment of the importance of CO2 photo-production in the global carbon cycle.