the particle-reactive thorium isotopes as natural "clocks," the geochemical approach provides 

 an independent method to quantify transformations. 



Almost every water parcel in a vertical water column profile on the slope will have, at 

 some recent point in time, been in contact with sediments and associated nepheloid layers. 

 Therefore, we expect to encounter resuspended or diagenetically altered POC and DOC at any 

 depth in the water column of the shelf or slope. In order to distinguish the terrestrial, water 

 column or benthic sources of DOC and POC, we will rely on the following tracers: 1) 

 biomarkers (e.g., loliolides originating mostiy from sediments, vs phytoplankton pigments such 

 as fucoxanthin or zeaxanthin, or lignin phenols from riverine sources), 2) radioactive and 

 stable isotopes (e.g., variations in 228Ra/226f^^ ^j^ jj^g ^^^gj. ^j^g ^g recent diffusion out of 

 margin sediments, variations in 5^^N due to different nitrogen pathways, variations in 5^^C due 

 to different carbon sources, variations in ^"^C due to recent bomb ^'*C02 uptake, old CO2 

 from upwelled deep water sources, or mixing with older forms of carbon). 



The compositional relationship between DOM, small particles, and aggregates can be 

 investigated by an analysis of constituent biomarkers. Biomarker analyses do not explicitiy 

 yield transformation rates, however they may serve to help identify major transformation 

 pathways and place mass balance constraints on competing transformation reactions. 

 Biomarker analyses also provide a knowledge of composition that is useful in designing 

 experimental systems to study the formation and fate of different carbon pools, both in the 

 laboratory and in the field. It is now widely recognized that analyses at the macromolecular 

 level may provide important and often unique information that is not attainable from 

 traditional biomarker analyses, as well as serve to integrate molecular level analyses with bulk 

 chemical properties. New developments in spectrometric methods (mass, nuclear magnetic 

 resonance, and infrared spectrometry) along with advances in chromatographic separation of 

 high molecular weight compounds, have made macromolecular analyses on complex samples 

 such as DOM and aggregates possible. Preliminary analyses have only recentiy been made for 

 DOM and small particles. To the best of our knowledge, no such analyses have been reported 

 for aggregates. Such studies may contribute significantly to our understanding of organic 

 matter transformations. 



E. Zooplankton Grazing and Production 



The primary importance of zooplankton, in terms of potential long-term removal of 

 carbon from the ocean-atmosphere system, lies in the transformation of carbon from one form 

 to another by means of their growth and grazing activities. To the extent that any of these 

 transformations have, on the community level, a significant net positive or negative effect, the 

 fate of the carbon in the planktonic system will be affected. For example, if protozoan grazers 

 feed primarily on particulate materials, excrete primarily dissolved and colloidal compounds, 

 and possess an average gross growth efficiency (body carbon produced/carbon ingested) of 

 40%, they will function as net transformers of POC (food) into DOC and colloidal organic 

 carbon (COC, waste products). Furthermore, if the primary fate of these protozoan grazers is 

 to be eaten by larger organisms, an additional effect will be the transformation of POC into 

 fewer, larger, and more mobile packages. 



The division of grazer-produced organic carbon into POC, COC and DOC, and the size 

 distribution of the POC component, will determine whether that carbon will tend to remain in 



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