Equilibrator-based measurements of dissolved methane in the surface ocean using an integrated cavity output laser absorption spectrometer

• Published in: Acta oceanologica Sinica 2015-06, Vol.34 (6), p.34-41
• Main Authors: Li, Yuhong, Zhan, Liyang, Zhang, Jiexia, Chen, Liqi
• Format: Article
• Language: English
• Subjects: Analytical methods; Balancing; Climatology; Earth and Environmental Science; Earth Sciences; Ecology; Engineering Fluid Dynamics; Environmental Chemistry; Freshwater; Inland water environment; Marine & Freshwater Sciences; Methane; Oceanography; Room temperature; Spatial distribution; Spectroscopy; Surface water; Time constant; Water masses; 吸收光谱仪; 平衡器; 海洋表面; 溶解; 甲烷测量; 积分; 输出光谱; 输出激光
• ISSN: 0253-505X; 1869-1099
• DOI: 10.1007/s13131-015-0685-9

A new off-axis integrated cavity output spectroscopy （ICOS） is coupled to Weiss equilibrator for continuous high- resolution dissolved methane measurement in the surface ocean. The time constant for the equilibrator in freshwater at room temperature is determined via dis-equilibration and re-equilibration experiments. The constant for methane is about 40 min. The system is calibrated using a standard gas of 3.980×10-6, and the precision of the ICOS for methane is 0.07%. This system is equipped onboard to measure the spatial distribution in methane concentrations of South Yellow Sea （SYS） along the cruise track from Shanghai to Qingdao. Result shows that the methane concentration varies from 2.79 to 36.36 nmol/L, reveals a significant pattern of methane source in SYS, and a distinct decreasing trend from south to north. The peak value occurs at the coast area outside mouth of the Changjiang River, likely to be affected by the Changjiang diluted water mass dissolving a large amount of rich in methane. Moreover, all the surface waters are oversaturated, air-to-sea fluxes range from 98.59 to 5 485.35 μmol/（m2·d） （average value （1 169.74±1 398.46） μmol/（m2·d））, indicating a source region for methane to the atmosphere. Key words： methane, equilibrator, off-axis integrated cavity output spectroscopy （ICOS）, South Yellow Sea