報告書番号

U01029

タイトル（和文）

SF6を用いた大気－海洋間のCO2気体交換過程の推定

タイトル（英文）

Estimation of the CO2 exchange process at the Air-Sea interface using SF6

概要 （図表や脚注は「報告書全文」に掲載しております）

温暖化防止のため海洋に隔離したCO2は、いずれ大気へ還流することが想定される。しかし、海洋中のCO2濃度の経年変化は微小であり、また生物活動・化学反応が関わるため、気体交換過程の正確な把握は困難であった。一方、大気・海洋中に存在する人工合成気体の六フッ化硫黄(SF6)は、生物に吸収されずかつ化学的にも安定なため、それを活用したCO2の気体交換過程の解明が期待されていた。 そこで、SF6の高精度測定手法を確立し、太平洋西部赤道海域においてSF6の測定を行ったところ、表層混合層(0～120m)と密度躍層(120～300m)においてSF6の存在が確認された。従来の気体交換係数の時間スケールは数時間～数週間であったが、さらに長い時間スケール(約1年)の気体交換係数の知見がないことから、SF6の経年変化より検討した。

概要 （英文）

The sequestration of CO2 in the middle layer of the ocean is one of the promising measures to prevent global warming in the future. In such the measure, injected CO2 in the ocean would return to the atmosphere after a certain elapsed time. As the long-term air-sea gas exchange process of CO2 is affected by the biological and chemical processes in the ocean, it is difficult to exactly estimate the gas exchange rate of injected CO2. On the other hand, the sulfur hexafluoride (SF6) is an industrial gas and discharged in the atmosphere, and it is biologically and chemically stable in the ocean. If we would observe a low concentration of SF6 dissolved in the ocean, it may be possible for us to elucidate the CO2 gas exchange process. In this report, the measurement system of SF6 was newly developed with a high accuracy. The sea water contained SF6 was sampled in the Western Equatorial Pacific Ocean(WEPO). The concentrations of SF6 in the sample water were analyzed by the new measurement system. As a result, SF6 was detected both in the mixing layer and the pycnocline. In the WEPO, the mixing layer ranges from the sea surface to 120m depths and the pycnocline ranges from 120m to 300m depths, because they are affected by equatorial upwelling. Previously the gas exchange coefficients of CO2 have been studied only in the short time scale, which order is from hours to weeks. In this report, the inter-annual change of SF6 in the ocean was estimated and the long term air-sea gas exchange of CO2 was evaluated by the result of SF6.

報告者

キーワード