We demonstrate the ability to obtain accurate estimates of pH and carbonate mineral saturation state (Ω) from an Argo profiling float in the NE subarctic Pacific. Using hydrographic surveys of the NE Pacific region, we develop empirical algorithms to predict pH and Ω using observations of temperature (T) and dissolved O₂. We attain R² values greater than 0.98 and RMS errors of 0.018 (pH), 0.052 (Ω_arag), and 0.087 (Ω_calc) for data between 30–500 m, σ < 27.1. After calibrating optode-based O₂ data, we apply the algorithms to T and O₂ data from an Argo profiling float to produce a 14 month time-series of estimated pH and Ω_arag in the upper water column of the NE subarctic Pacific. Comparison to independent data collected nearby in 2010 indicates pH and Ω_arag estimates are robust. Although the method will not allow detection of anthropogenic trends in pH or Ω_arag, this approach will provide insight into natural variability and the key biogeochemical controls on these parameters. Most importantly, this work demonstrates that an assemblage of well-calibrated regional algorithms and Argo float data can be used as a low-cost, readily-deployable component of a global ocean carbon observing strategy.

Juranek L. W., Feely R. A., Gilbert D., Freeland H., & Miller L. A., 2011. Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy. Geophysical Research Letters 38: L17603. Article (subscription required).