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 (Omega) 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 Omega using observations of temperature (T) and dissolved O-2. We attain R-2 values greater than 0.98 and RMS errors of 0.018 (pH), 0.052 (Omega(arag)), and 0.087 (Omega(calc)) for data between 30-500 m, sigma(theta) < 27.1. After calibrating optode-based O-2 data, we apply the algorithms to T and O-2 data from an Argo profiling float to produce a 14 month time-series of estimated pH and Omega(arag) in the upper water column of the NE subarctic Pacific. Comparison to independent data collected nearby in 2010 indicates pH and Omega(arag) estimates are robust. Although the method will not allow detection of anthropogenic trends in pH or Omega(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. Citation: Juranek, L. W., R. A. Feely, D. Gilbert, H. Freeland, and L. A. Miller (2011), Real-time estimation of pH and aragonite saturation state from Argo profiling floats: Prospects for an autonomous carbon observing strategy, Geophys. Res. Lett., 38, L17603, doi:10.1029/2011GL048580.