Elucidation of global carbon cycle by measuring atmospheric oxygen concentration and carbon isotoptic ratio of carbon dioxide

为了定量地评估人类活动排放到大气中的二氧化碳（CO2）有多少被陆地生物圈和海洋吸收，人们采用了两种方法。第一种方法是通过测量二氧化碳浓度和碳同位素比（d13C），第二种方法是通过测量氧气（O2）和二氧化碳浓度。1984 ~ 2000年陆地生物圈和海洋对人为CO2的吸收分别为1.21和1.59 GtC/yr。因此，陆地生物圈和海洋是人为二氧化碳的汇。这些CO2汇的强度每年都在变化，并且很明显生物圈CO2汇的变化是对厄尔尼诺事件和皮纳图博火山爆发引起的异常天气的响应。另一方面，1999 - 2003年陆地生物圈和海洋生物圈的CO2汇分别为1.1±1.0和2.0±0.6 GtC/yr。我们比较了从这些独立的方法中获得的结果，这些结果大多是相互重叠的。1994 ~ 2000年CO2浓度和d13C值为0.90 GtC/yr， O2和CO2浓度值为1.1±1.0 GtC/yr。1994 ~ 2000年CO2浓度和d13C值为1.73 GtC/yr， O2和CO2浓度值为2.0±0.6 GtC/yr。由于用两种不同的方法得到的结果相当一致，因此认为可以得到可靠的结果。

In order to evaluate quantitatively how much carbon dioxide (CO2) emitted to the atmosphere by human activities is absorbed by the land biosphere and the ocean, two kinds of approaches have been made. The first approach was made by using measurements of CO2 concentration and the carbon isotopic ratio (d13C), and second was made by using measurements of oxygen (O2) and CO2 concentrations. Absorption of anthropogenic CO2 by the land biosphere and the ocean for the period of 1984 to 2000 were 1.21 and 1.59 GtC/yr, respectively by analyzing CO2 concentration and d13C. As a result, the land biosphere and the ocean were the sink of anthropogenic CO2. The strengths of these CO2 sinks were changed year by year, and it became clear that the biospheric CO2 sink changed in response to El Nino event and abnormal weather caused by the Pinatubo eruption. On the other hand, these CO2 sinks for the period of 1999 to 2003 evaluated by O2 and CO2 concentrations were estimated to be 1.1±1.0 and 2.0±0.6 GtC/yr for the land biosphere and the ocean, respectively. We compared the results obtained from these independent approaches for the period that has overlapped each other mostly. As for the biospheric CO2 sink, the value obtained from CO2 concentration and d13C for the period of 1994 to 2000 was 0.90 GtC/yr, and that obtained from O2 and CO2 concentrations was 1.1±1.0 GtC/yr. As for the oceanic CO2 sink, the value obtained from CO2 concentration and d13C for the period of 1994 to 2000 was 1.73 GtC/yr, and that obtained from O2 and CO2 concentrations was 2.0±0.6 GtC/yr. Since the results obtained by two different approaches agreed quite well, it is thought that reliable results could be obtained.