Tanioka, Tatsuro2020-01-102020-01-102019-11https://hdl.handle.net/11299/211324University of Minnesota Ph.D. dissertation. November 2019. Major: Earth Sciences. Advisor: Katsumi Matsumoto. 1 computer file (PDF); ix, 147 pages.Photosynthesis by ocean algae (phytoplankton) contributes roughly half of the earth's net carbon production. Organic matter produced using carbon dioxide in the atmosphere not only supports marine food webs, but also acts as a climate stabilizer, because carbon is subsequently transported to the deep ocean and stored there for thousands of years. Attempts to model global marine biological production and its impacts on global biogeochemical cycles often assume a constant elemental stoichiometry of carbon, nitrogen, and phosphorus in phytoplankton biomass. This ratio, known as the Redfield ratio, was determined on the basis of an analysis of many samples of marine plankton collected over 70 years ago. This notion is well established in the oceanographic community but there is no clear physiological justification for why the C:N:P ratios in phytoplankton should strictly follow the Redfield ratio. Many recent studies revealed that C:N:P ratio of particulate organic matter can deviate significantly from the Redfield Ratio with some noticeable spatial and temporal variability. Studies suggest that factors such as nutrient availability, light, and temperature play a crucial role in modifying C:N:P ratio of phytoplankton. In this dissertation, I investigate the roles of marine phytoplankton stoichiometry in the global marine biogeochemical dynamics by combining meta-analysis, numerical modeling, and remote sensing. I propose a mechanistic framework for predicting C:N:P in phytoplankton under different environmental conditions and I incorporate this framework into an Earth System Model to show their effects on global carbon cycle. I also present results on how the change in elemental composition of phytoplankton could affect the feeding behavior of zooplankton as well the ecosystem stoichiometry. Finally, I show that C:N:P is closely tied to the rate at which oxygen is consumed during organic matter remineralization and I propose that the change in phytoplankton stoichiometry could ameliorate the rate of marine deoxygenation. In summary, C:N:P of phytoplankton is flexible and will play key roles in future global ocean biogeochemical dynamics.enCarbon cycleDeoxygenationElemental cycleElemental stoichiometryPhytoplanktonRedfield RatioThesis or Dissertation