STRENGTHS AND LIMITATIONS OF PROPOSED RESEARCH 



Organic carbon deposited to the sediments is metabolized over a long time, with decreasing 

 rates over time. My approach will provide estimates and assist with explanations for organic 

 carbon preservation in various sedimentary regimes on various time scales. My ability to explain 

 the terrigenous-to-marine transition will be limited by the ability of stable isotopes (and 

 biomarkers if they are included in the study) to quantitate the various mixes of terrestrial vs. 

 marine organic matter. Similarly, the measures of labile organic matter, while the best available 

 (I believe), offer only imperfect estimates of this fraction of the organic matter present. 



STATUS OF RESEARCH 



Progress over the last two years has seen the publication of Mayer (1994, Geochim. 

 Cosmochim. Acta 58:1271-1284), which demonstrates clearly that the amount of organic carbon 

 burial in many continental shelf environments around the world is correlated to the adsorption 

 capability of the sediments. An empirical case for this control derives from the organic 

 carbon-surface area correlations, with a slope of 0.9 mg-OC per m 2 of mineral surface area. A 

 causal mechanism for protection of organic matter at this concentration is hypothesized to be 

 protection from hydrolytic enzymes of heterotrophs by adsorption into pores too small to allow 

 enzyme entry, a hypothesis which is supported by pore size data on the mineral surfaces. A 

 second paper is now in press (Chem. Geol.), which extends the relationships of the first paper 

 to a number of terrestrial soil and marine continental slope and deep sea environments. The 

 second paper explores the implications of this adsorption control in more detail, extending its 

 impact to temporal as well as spatial variations in organic matter burial. 



We are continuing to collect and analyze samples in ocean margin environments to better 

 delineate the spatial extent of these correlations. A few cores from the Hatteras slope area have 

 been analyzed (cores courtesy of L. Benninger), and show consistency with the global data set 

 (albeit with remarkably high organic carbon concentrations at the slope depocenter). A frequent 

 question when I present this work at meetings regards the meaning of the term 

 "monolayer-equivalent". I am therefore spending considerable effort this year exploring how to 

 measure the extent of organic matter coverage on mineral surfaces. My approach involves using 

 the different enthalpies of adsorption of argon and nitrogen gases on mineral vs. organic surfaces. 

 There is some success, though the outcome is yet uncertain. 



Keywords: carbon burial, carbon accumulation, isotopes, grain size, sediment topography 



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