Long‐term monitoring of carbon and oxygen isotope ratios of stratospheric CO₂ over Japan

Abstract

We have been measuring stable isotopic ratios of carbon (δ 13 C) and oxygen (δ 18 O) of carbon dioxide in the stratosphere (18–35 km altitudes) over Japan since 1985, presenting here the first temporal δ 13 C and δ 18 O records between 1985 and 1991. The stratospheric δ 13 C is gradually decreasing due to anthropogenic effects with a rate of approximately −0.03‰ y −1 , which is similar to the tropospheric value. The previously found 18 O enrichment in stratospheric CO 2 has been maintained almost steadily during the 6 years, with a monotonous δ 18 O increase with increasing altitude up to 35 km over Japan.