Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy

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 (Ωarag), and 0.087 (Ωcalc) for data between 30–500 m, σθ < 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 Ωarag in the upper water column of the NE subarctic Pacific. Comparison to independent data collected nearby in 2010 indicates pH and Ωarag estimates are robust. Although the method will not allow detection of anthropogenic trends in pH or Ωarag, 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).


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