Seeing a Deep Ocean CO2 Enrichment Experiment in a New Light: Laser Raman Detection of Dissolved CO2 in Seawater

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• 作者：Rachel M. Dunk ; Edward T. Peltzer ; Peter M. Walz ; and Peter G. Brewer
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：December 15, 2005
• 年：2005
• 卷：39
• 期：24
• 页码：9630 - 9636
• 全文大小：385K
• 年卷期：v.39,no.24(December 15, 2005)
• ISSN：1520-5851

文摘

We used a newly developed in situ laser Ramanspectrometer (LRS) for detection of elevated levels ofdissolved CO₂ in seawater. The experiment was carriedout at 500 m depth, 6 mages/entities/deg.gif">C, to examine new protocols fordetection of CO₂-enriched seawater emanating from a liquidCO₂ source in the ocean, and to determine currentdetection limits under field conditions. A system of twointerconnected 5 L chambers was built, with flow betweenthem controlled by a valve and pump system, and thisunit was mounted on an ROV. The first chamber was fittedwith a pH electrode and the optical probe of the LRS. Inthe second chamber ~580 mL of liquid CO₂ was introduced.Dissolution of CO₂ across the CO₂-seawater interfacethen occurred, the valves were opened, and a fixed volumeof low-pH/CO₂-enriched seawater was transferred to thefirst chamber for combined pH/Raman sensing, where weestimate a mean dissolution rate of ~0.5 (mages/entities/mgr.gif">mol/cm²)/s.This sequence was repeated, resulting in measurement ofa progressively CO₂ enriched seawater sample. Therapid in-growth of CO₂ was readily detected as the Fermidyad of the dissolved state with a detection limit of~10 mM with spectral acquisition times of 150 s. Thedetection of background levels of CO₂ species in seawater(~2.2 mM, dominantly HCO₃^-) will require an improvementin instrument sensitivity by a factor of 5-10, whichcould be obtained by the use of a liquid core waveguide.