A study of organic carbon dynamics in aquatic environments using bulk, molecular and compound-specific isotopic methods

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I propose to continue research initiated in the past 3.5 years on the forms, distributions and preservation of quantitatively important and uncharacterized components of organic matter (OM) in aquatic systems, as well as on the use of molecular proxies for determining organic carbon sources and reaction histories. This work builds on previous evidence that the concentration and freshness of sedimentary OM are related to their physical forms, chemical compositions and cumulative exposure to UV and O2 during their transit from the surface to deep waters and burial in sediments. We are specializing in the development of bulk and molecular methods to probe the different and often opposing theories on the factors responsible for the preservation of OM in sediments. The main thrust of our research is to use these newly developed tools to deepen our understanding of the controls on the preservation of quantitatively important components of sedimentary OM, especially the predominant non-hydrolysable O2-sensitive, black carbon, molecularly-uncharacterized, and physically shielded fractions, and to probe their chemical composition and role in the global carbon cycle. The following major questions will be addressed: (1) What are the forms and micron-scale distributions of the non-hydrolysable, black carbon and physically shielded components preserved in marine sediments? Do these components exhibit different sensitivities to degradation under oxic versus anoxic conditions, and if so, what are the physical and chemical reasons for these contrasts? (2) What is the importance of minerals in the sequestration of OM in the deep ocean and in the preservation of labile biochemicals in marine sediments? (3) What is the global importance of soot/graphitic black carbon preservation in the biogeochemical cycles of carbon and oxygen? (4) What is the chemical, isotopic and molecular (including compound-specific isotopes) composition of the overwhelming fraction (50-75%) of marine dissolved organic carbon that still today is not recovered when using the traditional ultrafiltration and solid-phase extraction methods?