Given the hypothesized role for the marine nitrogen cycle in governing carbon cycling, reconstructions of nitrogen biogeochemistry are critical to improve our understanding of global geochemical cycles. Scientists from Harvard University and the University of Rhode Island propose to complete their development of a new analytical method to achieve reliable, high-throughput analyses of nitrogen isotope composition (del15N) values of sedimentary porphyrins. Values of porphyrin-del15N should reflect both the overall state of the nitrogen cycle, and in particular, conditions of nutrient supply and demand in the surface ocean. In addition, the scientists plan to measure the nitrogen isotopic fractionation in prokaryotes and eukaryotes, Last Glacial Maximum-to-Holocene sediments from sites characterized by different nitrogen dynamics, and analyze Mediterranean sapropels and Cretaceous Ocean Anoxic Events. The goal of this research is to help constrain the global importance of denitrification and nitrogen fixation. As regards broader impacts, results from this research will improve our understanding of water column biogeochemistry which will be critical in predicting the response of the nitrogen cycle to climatic events. One graduate student at Harvard University and one undergraduate student from the University of Rhode Island will be supported and trained.
