The Southern Ocean plays a key role in regulating past and present atmospheric CO2 concentrations through primary production (carbon pump) and ventilation of the CO2-rich deep waters. Evaluating the importance of the carbon pump through time is of primary importance to understanding climate change. One hypothesis proposed to explain the observed lower glacial CO2 concentrations is that changes in the supply of Fe and water column stratification influenced biological productivity in the Southern Ocean which altered the nutrient composition of waters flowing from the Southern Ocean to low latitude oceans. Changes in biological production are difficult to assess but two new tools, the Si and N isotopic compositions of diatoms, now allow estimates of nutrient consumption over time. These techniques will be applied to fossil diatom samples from existing sediment cores to evaluate changes in nutrient use in the Southern Ocean during the past 2 glacial events. Combining theses new results with existing proxies, such as biogenic silica fluxes and dust/Fe records, will provide estimates of past nutrient dynamics in the Southern Ocean and test the hypothesis of changes in Southern Ocean and global production through nutrient use. This research will lead to a better understanding of how nutrient dynamics and biogeochemical cycling affects the climate of the Earth. The broader impacts include interaction with local K-12 teachers to help younger students understand past and present climate changes. The project will also support the early careers of two young women scientists who have not had prior NSF funding as well as provide training of both graduate and undergraduate students. The results of this project will be broadly disseminated and data will be posted on web databases such as the National Geophysical Data Center. This project is jointly funded by the Ocean Sciences Marine Geology & Geophysics Program, Polar Programs Antarctic Earth Sciences Program and Emerging Topics in Biogeochemical Cycle.
