insights into present and past patterns of carbon fixation and 

 cycling. 



b. Fluxes: Isotopic methods could be used to study net 

 fixation by using H^CCU at levels just above background in large 

 enclosure studies in lakes and oceans. Such studies could reveal 

 the ratio of carbon fixed to that incorporated into various primary 

 producers, and add insight into the types of carbon compounds most 

 useful as indicators of primary productivity, recycling of carbon, 

 and burial of carbon. 



c. Fates: Not only are the isotopic methods discussed above 



relevant to the fates and burial of carbon (i.e., for estimating 



• . l "} 1 ? 



the activity of reprocessing by 1J C/ 1C C) , but many modern techniques 



of molecular genetics are also relevant. For instance: 



i) reprocessing of carbon can be estimated by carbon 



isotopic analyses; 



ii) the existence, abundance, and activities of organisms 



active in diagenetic cycling of carbon; and 



iii) indications of microbes and enzymes present in the 

 environment, by using nucleic acid probes and immunological 

 methods. 



Coupling of type (b) studies with those discussed in (a) may 

 provide valuable insights into local and global carbon cycling. 

 For example, within deep marine or lacustrine muds, species could 

 be identified which have disproportionately contributed to organic 

 carbon sedimentation, by examining residual DNA fragments. The 

 contribution of broader taxonomic groups may be identifiable from 

 ratios of stable isotopes (e.g., lt C: 1 °C of carbon compounds, such 

 as fatty acid and lipid skeletons, and residues) . The ratio of 

 identifiable to amorphous material may provide insight into the 

 decay processes that precede sequestration. Various isotopic 

 dating methods of depth-graduated samples can estimate carbon flux 

 to carbon sequestered. Similar methods apply to the study of 

 terrestrial soils. 



Calcification 



In the oceans, photosynthetic C0 2 fixation reduces the partial 

 pressure of C0 2 , thereby increasing the C0 2 diffusion gradient 

 between the atmosphere and the ocean. In contrast, calcification 



II-6 



