title: In situ sensor technology for simultaneous spectrophotometric measurements of seawater total dissolved inorganic carbon and pH.
abstract: 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 ∼ 90 s. 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.
authors.affiliation: †Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, McLean 203, MS #8, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Zhaohui Aleck
authors.initials: ZA
authors.lastname: Wang
authors.affiliation: ‡Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Frederick N
authors.initials: FN
authors.lastname: Sonnichsen
authors.affiliation: ‡Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Albert M
authors.initials: AM
authors.lastname: Bradley
authors.affiliation: †Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, McLean 203, MS #8, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Hoering
authors.affiliation: ‡Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Lanagan
authors.affiliation: †Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, McLean 203, MS #8, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Sophie N
authors.initials: SN
authors.lastname: Chu
authors.affiliation: ‡Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Terence R
authors.initials: TR
authors.lastname: Hammar
authors.affiliation: ‡Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States.
authors.forename: Richard
authors.initials: R
authors.lastname: Camilli
mesh_terms: D002244:Carbon / Q000032:analysis*; D004867:Equipment Design; D006863:Hydrogen-Ion Concentration; D012623:Seawater / Q000032:analysis* / Q000737:chemistry; D013053:Spectrophotometry / Q000295:instrumentation / Q000379:methods*
chemical_list: D002244:Carbon