9521086 Verity Non-living particulate organic matter, called detritus, plays an important role in the cycling of carbon and macronutrients in water column environments, especially in the ocean. Assessments of carbon bound in detrital particles typically exceed estimates of carbon from plankton and are second only to dissolved organic carbon. Detritus is a highly dynamic medium which provides a substrate for microbial respiration of dissolved organic carbon and its transformation into particular organic carbon and a substrate for abiotic condensation of exopolymers, secreted from bacteria and phytoplankton. However, the ability to quantify detritus in situ has remained an unresolved problem. The proposed research will investigate variability in particulate detrital carbon (and nitrogen):volume ratios using controlled laboratory experiments. Quantification will be conducted using a newly developed fluorescent labeling technique followed by imaging cytometry. Laboratory-derived data will be compared to field data from natural plankton communities in continental shelf waters. This work will allow accurate determinations of particulate detrital and plankton stock sizes, a necessary prerequisite to resolving the dynamic interchange of organic carbon and nitrogen between non-living and living resources, especially the downward flux and trophic transfer of such materials. ***
