title: In situ spectrophotometric measurement of dissolved inorganic carbon in seawater.
abstract: Autonomous in situ sensors are needed to document the effects of today's rapid ocean uptake of atmospheric carbon dioxide (e.g., ocean acidification). General environmental conditions (e.g., biofouling, turbidity) and carbon-specific conditions (e.g., wide diel variations) present significant challenges to acquiring long-term measurements of dissolved inorganic carbon (DIC) with satisfactory accuracy and resolution. SEAS-DIC is a new in situ instrument designed to provide calibrated, high-frequency, long-term measurements of DIC in marine and fresh waters. Sample water is first acidified to convert all DIC to carbon dioxide (CO2). The sample and a known reagent solution are then equilibrated across a gas-permeable membrane. Spectrophotometric measurement of reagent pH can thereby determine the sample DIC over a wide dynamic range, with inherent calibration provided by the pH indicator's molecular characteristics. Field trials indicate that SEAS-DIC performs well in biofouling and turbid waters, with a DIC accuracy and precision of ∼2 μmol kg(-1) and a measurement rate of approximately once per minute. The acidic reagent protects the sensor cell from biofouling, and the gas-permeable membrane excludes particulates from the optical path. This instrument, the first spectrophotometric system capable of automated in situ DIC measurements, positions DIC to become a key parameter for in situ CO2-system characterizations.
authors.affiliation: College of Marine Science, University of South Florida , 140 7th Avenue S., St. Petersburg, Florida 33701, United States.
authors.forename: Xuewu
authors.initials: X
authors.lastname: Liu
authors.forename: Robert H
authors.initials: RH
authors.lastname: Byrne
authors.forename: Lori
authors.initials: L
authors.lastname: Adornato
authors.forename: Kimberly K
authors.initials: KK
authors.lastname: Yates
authors.forename: Eric
authors.initials: E
authors.lastname: Kaltenbacher
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Ding
authors.forename: Bo
authors.initials: B
authors.lastname: Yang
mesh_terms: D002244:Carbon / Q000032:analysis*; D005431:Florida; D012623:Seawater / Q000032:analysis*; D013053:Spectrophotometry
chemical_list: D002244:Carbon