A new, in-situ sensing system, Channelized Optical System (CHANOS), was recently developed to make high-resolution, simultaneous measurements of total dissolved inorganic carbon (DIC) and pH in seawater. Measurements made by this single, compact sensor can fully characterize the marine carbonate system. The system has a modular design to accommodate two independent, but similar measurement channels for DIC and pH. Both are based on spectrophotometric detection of hydrogen ion concentrations. The pH channel uses a flow-through, sample-indicator mixing design to achieve near instantaneous measurements. The DIC channel adapts a recently developed spectrophotometric method to achieve flow-through CO2 equilibration between an acidified sample and an indicator solution with a response time of only ~90s. During laboratory and in-situ testing, CHANOS achieved a precision of ±0.0010 and ±2.5 µmol kg-1 for pH and DIC, respectively. In-situ comparison tests indicated that the accuracies of the pH and DIC channels over a three-week time-series deployment were ±0.0024 and ±4.1 µmol kg-1, respectively. This study demonstrates that CHANOS can make in-situ, climatology-quality measurements by measuring two desirable CO2 parameters, and is capable of resolving the CO2 system in dynamic marine environments.

Wang Z. A., Sonnichsen F. N., Bradley A. M., Hoering K. A., Lanagan T. M., Chu S. N., Hammar T. R. & Camilli R., in press. An in-situ sensor technology for simultaneous spectrophotometric measurements of seawater total dissolved inorganic carbon and pH. Environmental Science & Technology. Article (subscription required).