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Simultaneous measurement of concentration and isotope ratio of dissolved gases by using a continuous flow isotope ratio mass spectrometry and its application to oceanography

连续流同位素比质谱同时测量溶解气体浓度和同位素比及其在海洋学中的应用

基本信息

批准号：
16204045
负责人：
GAMO Toshitaka
金额：
$ 32.86万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

项目摘要

We have constructed a continuous flow isotope ratio mass spectrometric system by combining a gas chromatograph and an isotope ratio mass spectrometer equipped with differential pumping, in order to measure concentration and stable isotope ratio of dissolved gases simultaneously. The main targets are dissolved oxygen and hydrogen in seawater. The system was connected with vacuum lines which were prepared for extraction of these gases from water samples and their purification and pre-concentration. Seawater samples were taken with a CTD-Carousel water sampling system during the R/V Hakuho Maru KH-04-5, KH-05-2, KH-06-2 cruises in the western Pacific Ocean and the RAT Hansei Maru KT-05-11 cruise in the Japan Sea. We successfully estimated both the rate of O_2 consumption by bacterial organic matter decomposition (1.2 μmol kg^<-1> y^<-1> in the Japan Sea bottom water and 0.11 μmol kg^<-1> y<-1> in the Philippine Sea deep water) and isotopic fractionation factor of dissolved O_2 consumption (0.988 to 0.990). These values will be important standards to compare with those of future measurements for global change monitoring. As for dissolved hydrogen, we are in progress to achieve analytical precision high enough to analyze dissolved H_2 in natural seawater. Alternatively, we have measured dissolved H_2 and its δD values for submarine hydrothermal fluids from the Indian Ridge and back arc basins in the western Pacific for the first time. We have found uniquely deuterium depleted H_2 (δD: -800 to -700‰) for high temperature fluids from Southern Mariana Trough, in contrast with those (δD: -400 to -300‰) observed at Central Indian Ridge and Okinawa Trough, which are consistent with isotope fractionation equilibrium between H_2 and H_2O at high temperatures (300-400℃). The discovery of the low δD in the Southern Mariana Trough demonstrates other H_2 sources such as chemical reaction between H_2O and crushed rocks.

我们将气相色谱仪和同位素比质谱仪结合起来，采用差动抽气技术，建立了一套连续流动同位素比质谱系统，可同时测量溶解气体的浓度和稳定同位素比。主要目标是海水中的溶解氧和氢。该系统与真空管线连接，真空管线用于从水样中提取这些气体并对其进行纯化和预浓缩。在“Hakuho Maru KH-04-5”、“KH-05-2”、“KH-06-2”号考察船在西太平洋巡航和“RAT Hansei Maru KT-05-11”号考察船在日本海巡航期间，用CTD-Carnival水取样系统采集了海水样品。我们成功地估算了细菌分解有机物消耗O_2的速率（日本海底层水为1.2 μmol kg^<-1>y^<-1>，菲律宾海深层水为0.11 μmol kg^<-1>y <-1>^）和溶解O_2消耗的同位素分馏因子（0.988 ~ 0.990）。这些数值将成为与未来全球变化监测测量值进行比较的重要标准。对于溶解氢，我们正在努力使分析精度达到足以分析天然海水中溶解H_2的水平。此外，我们还首次测量了西太平洋印度洋脊和弧后盆地海底热液的溶解H_2及其δD值。我们在南马里亚纳海槽的高温流体中发现了独特的贫氘H_2（δD：-800 ~-700‰），而在中印度洋脊和冲绳海槽的高温流体中发现了贫氘H_2（δD：-400 ~-300‰），这与高温（300-400℃）下H_2和H_2O的同位素分馏平衡相一致。南马里亚纳海槽低δD的发现表明H_2还有其它来源，如H_2O与岩石之间的化学反应。