| Summary: | The Southern Ocean plays an important role in the ocean’s uptake of heat and carbon yet the processes controlling this uptake are not well understood. To date, more than 100 biogeochemical profiling floats that measure water column pH, oxygen, nitrate, fluorescence, and backscattering at 10-day intervals have been deployed throughout the Southern Ocean as part of the Southern Ocean Carbon and Climate Observations and Modeling Project (SOCCOM). Empirical algorithms are developed from shipboard bottle data that estimate pH in the Pacific sector of the Southern Ocean. These algorithms are applied to estimate pH on floats with no pH sensors and to validate and adjust sensor data from floats with pH sensors. The adjusted float data provide, for the first time, full seasonal cycles in surface and water column pH on weekly resolution throughout the Southern Ocean, including under sea ice. These pH data are then used to derive other carbonate system parameters, such as dissolved inorganic carbon, the saturation state of aragonite, and the partial pressure of carbon dioxide (pCO₂). Detailed analysis of the uncertainties in these derived parameters as well as comparisons with existing data and climatologies suggest that despite their increased uncertainty relative to direct measurements, these float-derived carbonate system parameters can be used to improve climatological and model-based estimates for oceanic carbon flux, as well as to increase knowledge of spatial, seasonal, and interannual variability in air-sea carbon flux. Float-based climatological seasonal cycles for all carbonate system parameters for the years 2014-2017 are calculated and drivers controlling the seasonal cycles are parsed out and examined across the frontal regions. The float-based climatologies are systematically compared with existing climatologies as well as with several fully-coupled Earth System Models (ESMs). Significant differences are found in this comparison suggesting that a previous lack of wintertime data has led to underestimations of ...
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