Ocean Circulation, Oxygen and Nutrient Cycles During the Last Glacial Period

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Ocean Circulation, Oxygen and Nutrient Cycles During the Last Glacial PeriodAndreas Schmittner-BoeschOregon State UniversityAbstractThis proposal seeks to test a primary hypothesis that observed millennial variations of sedimentary nitrogen isotope data from the N. Pacific during the last ice age reflect the collapse of North Atlantic Deep Water formation, which then led to a global decrease in upper-ocean nutrient concentrations and plankton productivity. This ecological shift in-turn led to reduced remineralization of organic matter, shrinkage of the oxygen minimum zones, and a decline in denitrification on a global scale, with a rapid response on the scale of hundreds of years. To address this question the PI's will embed a model of nitrogen isotope cycling in a newly improved coupled atmosphere-ocean model of intermediate complexity that includes biogeochemistry, and is capable of multi-millennial runs. Simulations with this model and comparison with the marine geological record will provide new and important information on mechanisms controlling past changes in ocean circulation, productivity, oxygen and nutrient cycling. Several elements of the model will be improved, including the physical circulation (tropical dynamics), and biogeochemistry (both primary biological components, and interactions with the bottom for benthic denitrification). The model will predict the regional distribution, amplitude, and timing of d15N (and other tracers) change for direct comparison with geologic data. Broader impacts include support for undergraduates and graduates and an early-career scientist who has not been funded previously by NSF. The PI's will develop their Earth system model and distribute it for community use at the end of the project.