During Ocean Drilling Program (ODP) Leg 184, cores were recovered from five sites (1143, 1144, 1146, and 1148) in the South China Sea (SCS) to study climate history over the last 30 m.y. Although the total organic carbon (TOC) content of sediments from the Leg 184 sites was not particularly high (0.2-0.5 wt%; maximum = ~1 wt%), it records the source, productivity, and preservation of organic matter (OM) and provides sufficient material to be well within the analytical capability of modern, sensitive analytical laboratory instruments that measure 
13C isotopic compositions. Organic matter in marine sediments can be a mixture of marine and land derived. The land-sourced OM signal is related to climate, erosion, and transport of bulk land materials (organic and mineral) to the sea. The relative amount of land-sourced OM can record this change with time.
The concentrations of TOC and 13C isotopes can often help define the source and depositional environment of organic matter. Carbon isotopes are used to define the relative amounts/sources of OM preserved in the sediments (Sackett, 1964; Nissenbaum and Kaplan, 1972; see also a recent summary of marine organic matter in Stein, 1991). The land-plant stable 13C isotope value is determined from direct measurement of "woody" material in the sediment; the marine isotope value is the heaviest 13C value measured for the bulk sediment. Thus, 13C determination for hand-picked pieces of "woody" material can be used to establish a land-plant isotopic end-member for a sediment carbon source budget.
Measurements of the 13C isotope variation in the bulk OM can be used to assess the contribution of land-derived OM in the sediment, which may give information about the relative importance of productivity, preservation, water depth, and distance from land. For example, in a perfect world, if woody OM yields a 13C value of -26
and most marine bulk OM yields -20, then other bulk samples with 13C values of -23 and -21.5 contain 50% and 25%, respectively, land-sourced OM. In general, marine OM 13C values range from -18 to -22 (Druffel et al., 1992) and land (terrigenous) OM 13C values range from -24 to -30 (Opsahl and Zepp, 2001).
