Collaborative Researchl: A Quantitative Assessment of Mineral Ballasts in Carbon Export and Remineralization

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ABSTRACTOCE-0136370 / OCE-0136387 / OCE-0136318Sinking 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 particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the surface concentration of dissolved CO2 , and hence the rate at which the ocean can absorb CO2 from the atmosphere. The ability to predict quantitatively the depth profile of remineralization is therefore critical to predicting the response of the global carbon cycle to environmental change. In this study, researchers at the State University of New York at Stony Brook, the University of Washington, and the Skidaway Institute of Oceanography will collaborate with colleagues in Monaco and France to test the hypothesis that minerals produced by organisms, or introduced into the surface ocean by winds, critically influence carbon export to the deep ocean and sediments. They will carry out a multi-tracer approach to explicitly consider different mineral "ballast" types, along with the associated organic matter and radioisotopes. Their first hypothesis is that ballast minerals physically protect a fraction of their associated total organic matter, which persists to predominate over the unprotected fraction in the lower (1000 m) part of the water column. Understanding the mechanistic basis of such processes will require an understanding of organic-mineral interaction at the compound-specific level. They hypothesize secondly that the ratio of organic carbon to ballast is key to predicting variability in the export fluxes and sinking velocities of organic carbon as estimated using radiotracers. The overall goal is to develop a seamless description of carbon fluxes and associated mineral ballast fluxes throughout the water column. To achieve this goal, the research team will measure simultaneously a suite of properties that are thought to be indicative of fluxes. They will synthesize these measurements from the top of the water column to the sediments using a variety of modeling and statistical techniques. The strategy is to unite 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; and (iv) microbiology for its role in organic matter decomposition, and (v) modeling and statistical analyses to provide a process-based model of flux out of the euphotic zone to the sea floor.