Repet702 ABSTRACT Recent reports of nitrogen distribution in marine sediments offer the exciting prospect of tracking changes in the marine nitrogen cycle through time, including changes in paleoproductivity and paleonitrification. These developments show great promise in adding to our understanding of large-scale controls on marine production, carbon preservation in sediments, and the interplay between climate and geochemical cycling. In this project, the principal investigator will focus attention on the main impediment to using sedimentary nitrogen isotopes in paleo- oceanographic studies: namely, the large and non-quantifiable imprint of early diagenesis on the sedimentary N15 record. Specifically he will continue his studies of the N15 composition of sedimentary chlorophyll-a as a tracer for processes affecting surface water nutrient dynamics. This approach should be more reliable that using N15 for bulk sedimentary organic matter in which the N15 signature of surface conditions is convoluted with post-depositional changes in nitrogen chemistry since deposition at the sediment surface.
