In situ spectrophotometric measurement of dissolved inorganic carbon in seawater

Environmental Science & Technology
By: , and 

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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.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title In situ spectrophotometric measurement of dissolved inorganic carbon in seawater
Series title Environmental Science & Technology
DOI 10.1021/es4014807
Volume 47
Issue 19
Year Published 2013
Language English
Publisher ACS Publications
Contributing office(s) St. Petersburg Coastal and Marine Science Center
Description 9 p.
First page 11106
Last page 11114
Online Only (Y/N) N
Additional Online Files (Y/N) N