UC San Diego

Data-based estimates of marine biogeochemical cycling are essential for making accurate forecasts of changes to our planet's climate and ecosystems resulting from mankind's perturbations to the chemistry of the ocean and the atmosphere. In this thesis I present and apply novel methods for hydrographic data collection and analysis. The quality and coverage of hydrographic measurements must be balanced against the practical costs of the analyses. A system for efficient, semi-autonomous, and precise colorimetric seawater pH analyses is presented and assessed with the aim of decreasing the investment required for this measurement. An inverse model constructed to estimate rates of organic matter degradation, rates of calcium carbonate dissolution, measurement covariance resulting from organic matter degradation, and the length of time that a measured water parcel has been out of contact with the atmosphere is presented and applied in the Southern Ocean. Model estimates are compared to estimates obtained from similar inverse methods that neglect either diapycnal mixing or mixing altogether, and significant differences are found. This supports the findings of several recent research efforts urging caution when interpreting inverse methods that neglect mixing. Climate models and ocean and atmospheric monitoring suggest that the Southern Ocean is undergoing long-term changes in its freshwater budget, heat budget, gas exchange processes, and circulation patterns. I examine and inverse model the effects of changes in biogeochemical processes on hydrographic properties using differences between datasets collected more than a decade apart in the Pacific sector of the Southern Ocean. Results indicate a continuation of previously observed warming and freshening trends in intermediate and mode waters and evidence for an increase in the Ekman divergence driven upwelling in the Antarctic Circumpolar Current