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Using cavity ringdown spectroscopy for continuous monitoring of δ 13 C(CO 2 ) and ƒCO 2 in the surface ocean
Author(s) -
Becker M.,
Andersen N.,
Fiedler B.,
Fietzek P.,
Körtzinger A.,
Steinhoff T.,
Friedrichs G.
Publication year - 2012
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2012.10.752
Subject(s) - seawater , dissolved organic carbon , fugacity , trace gas , carbon dioxide , atmosphere (unit) , isotopes of carbon , analytical chemistry (journal) , stable isotope ratio , isotope , flux (metallurgy) , chemistry , spectroscopy , environmental science , atmospheric sciences , environmental chemistry , meteorology , oceanography , geology , physics , total organic carbon , organic chemistry , quantum mechanics
The role of the global surface ocean as a source and sink for atmospheric carbon dioxide and the flux strengths between the ocean and the atmosphere can be quantified by measuring the fugacity of CO 2 (ƒCO 2 ) as well as the dissolved inorganic carbon (DIC) concentration and its isotopic composition in surface seawater. In this work, the potential of continuous wave cavity ringdown spectroscopy ( cw ‐CRDS) for autonomous underway measurements of ƒCO 2 and the stable carbon isotope ratio of DIC [δ 13 C(DIC)] is explored. For the first time, by using a conventional air‐sea equilibrator setup, both quantities were continuously and simultaneously recorded during a field deployment on two research cruises following meridional transects across the Atlantic Ocean (Bremerhaven, Germany—Punta Arenas, Chile). Data are compared against reference measurements by an established underway CO 2 monitoring system and isotope ratio mass spectrometric analysis of individual water samples. Agreement within ΔƒCO 2 = 0.35 µatm for atmospheric and ΔƒCO 2 = 2.5 µatm and Δδ 13 C(DIC) = 0.33‰ for seawater measurements have been achieved. Whereas “calibration‐free” ƒCO 2 monitoring is feasible, the measurement of accurate isotope ratios relies on running reference standards on a daily basis. Overall, the installed CRDS/equilibrator system was shown to be capable of reliable online monitoring of ƒCO 2 , equilibrium δ 13 C(CO 2 ), δ 13 C(DIC), and p O 2 aboard moving research vessels, thus making possible corresponding measurements with high spatial and temporal resolution.