Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the ocean interior. During its transit towards the sea floor, most (usually >90%) of particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the depth profile of dissolved CO2, including its concentration in the surface mixed layer, and hence the rate at which the ocean can absorb CO2 from the atmosphere. Recent modeling studies have shed new light on the mechanisms that are responsible for the shapes of POC profiles. It appears that the presence of mineral ballasts (silicates, carbonates, and dust) may account for most of the variability in POC delivery to the sea floor. The ability to predict the formation and subsequent dissolution of ballasts as particles descend may therefore be critical to predicting quantitatively and mechanistically the global implications of carbon fixation for global climate change.
In this project, U.S. researchers at the State University of New York at Stony Brook, the Skidaway Institute of Oceanography, and the University of Washington will continue their work with French and Spanish colleagues on a multi-tracer study of different ballast types, along with their associated organic matter and radioisotopes. The research strategy brings together the power of several disciplines: (i) organic geochemistry for characterizing organic matter in protected and unprotected forms and determining its degradation state; (ii) radiochemistry for assessing processes and time-scales involved in particle dynamics and transport; (iii) zooplankton ecology for assessing radioisotope partitioning and organic biomarker alteration; (iv) microbiology for its role in organic matter decomposition, and (v) modeling and statistical analysis to provide a process-based model of flux from the photic zone to the sea floor. The research team now expects to resolve changes in flux, organic matter and mineral ballast composition, and remineralization length scale through the mid-water depth "twilight zone" of the Mediterranean Sea and possibly the Atlantic Ocean near the Canary Islands.
Broader impacts: Our project should contribute to a better mechanistic understanding of the global carbon cycle. If a more sophisticated understanding of the ocean's response to increased levels of carbon dioxide can be developed, then more reasonable choices between political alternatives are possible. The project also features a substantial component for training of graduate students and postdoctoral scholars in the marine sciences. Additionally, the research effort will foster international cooperation, since it is highly dependent on collaborative linkages between American oceanographers and colleagues at the IAEA Marine Environment Laboratory (Monaco), the CNRS Laboratory of Marine Microbiology (Marseille), and the Autonomous University of Barcelona.
