This research involves the application of novel "in -source" mass spectrometric (MS) techniques for the molecular-level characterization of (sub)-microgram quantities of particulate organic matter (POM). The overall objective is to relate changes in POM composition to water column-based biogeochemical processes and to assess the importance of these processes in determining the chemical characteristics of sedimentary organic matter. Observed variations in POM composition will be interpreted in the context of current concepts for organic matter preservation. This objective will be pursued by investigating the composition of organic matter in samples of phytoplankton populations, particulate matter and surface sediments from high productivity (Peru Upwelling region) and oligotrophic (Sargasso Sea) Oceanic environments. The analytical approach adopted seeks to overcome several limitations which currently prevent the application of molecular markers as routine tools in marine geochemistry. Specifically, in- source MS offers advantages as a rapid, high sensitivity method which can be used to study compositional features of complex mixtures over a wide range of molecular sizes and polarities. The major focus is placed upon structural aspects of macromolecular constituents of POM, however, an assessment of lipid composition will also be made in an attempt to provide a more holistic perspective of POM transformation. The inherent sensitivity of in- source MS will be exploited by studying compositional variations in sub-factions of POM separated by flow cytometry. In this way, chemical variations can be related to well-defined particle characteristics (size, shape, chlorophyll content), enabling systematic relationships to be established between the composition of phytoplankton and POM.
