The goal of this project is to incorporate triple oxygen isotopes and oxygen/argon ratios into a hierarchy of ocean models to provide unique constraints on rates of photosynthesis and respiration. This, in turn, will increase the mechanistic understanding of the carbon cycle and improve ocean models used for future climate projections. The triple O2 isotopes and O2/Ar data will be used as constraints for an innovative modeling approach based on energy and its allocation into a variety of carbon pools. Firstly, their triple O2 isotopes and O2/Ar ratios will be incorporated into numerical, one-dimensional models for the Bermuda Atlantic Time-series Site (BATS) and the Hawaii Ocean Time-series site (HOT) to learn about isotope systematics in relatively simple systems. Next, the isotopes will be incorporated into the three-dimensional, ocean component of the global Community Climate System Model (CCSM), a model used extensively for studying human-driven climate change and carbon/climate feedbacks. It is hypothesized that the ratio of GPP to that of NPP varies spatially and temporally, and is dependent on environmental and biogeographical factors. The oxygen isotopes and the new modeling approach will be used to study the temperature dependence of rates of photosynthesis and respiration �?? a potential positive feedback to global warming �?? and to understand why nearly all biogeochemical models overpredict production in low productivity regions.