Reconstructing Glacial Nitrogen and Carbon Cycling Using Isotopes

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Measurements of nitrogen and carbon isotopes from deep-sea sediments document dramatic changes between the last ice age and the modern ocean. However, both nitrogen and carbon isotopes are influenced by different physical and biogeochemical processes, which makes their interpretation ambiguous. In this research, a process-based coupled model of climate, ocean circulation and biogeochemistry that includes carbon and nitrogen isotopes will be used in conjunction with sediment data in order to reconstruct glacial nitrogen and carbon cycles. The model will be amended with explicit iron cycling and global databases of nitrogen and carbon isotopes from Last Glacial Maximum and modern ocean sediments will be compiled. This approach allows testing of hypotheses concerning changes in the total ocean nitrogen inventory, polar nutrient consumption due to iron fertilization and their effects on atmospheric CO2 concentrations. The project continues collaboration between a climate modeler and a paleoceanographer from Oregon State University and international collaboration with a Canadian investigator from McGill University. Funding supports a graduate student, a summer workshop for 30 K-12 teachers from all parts of Oregon and a summer research experience for an undergraduate student at Oregon State University. In addition, the researchers will actively participate in both the Paleoclimate Modeling Intercomparison Project (PMIP) and in the new Paleo Carbon Modeling Intercomparison Project (PCMIP), efforts that evaluate the skill of climate models under paleoclimate conditions and improve understanding of past climate changes.