This project will evaluate uncertainties and biases associated with CFC-derived water-age and carbon cycling estimates in the North Pacific Ocean that result from CFC under-saturations in the mixed layer, ocean mixing and ocean variability. Model experiments with the Hallberg Isopycnal Model (HIM) will be made to investigate the sensitivity of water mass ages based on pCFC age and transit time distribution (TTD) techniques and of anthropogenic CO2 concentrations based on TTD and C* techniques to mixed layer boundary conditions and the use of hindcast versus climatological forcing. In addition, the PI will explore how oxygen utilization rates (OURs) are influenced by these mechanisms and by the choice out of a few ways to estimate age. The results from the modeling study will be applied to the U.S. CLIVAR repeat data in the North Pacific, and will help determine biogeochemical rates such as oxygen utilization, carbon export and calcium carbonate dissolution. Together the data and modeling components of this project will provide insight on how decadal and climate variability over the North Pacific is reflected in the ocean interior tracer distributions and how well CFC-based methods for calculating water mass ages, anthropogenic CO2, and OURs can resolve true changes in these quantities in the ocean.