長鎖脂肪酸の炭素同位体比を用いて過去の大気中二酸化炭素濃度を復元する試み

抄録

Atmospheric carbon dioxide (CO₂) is an essential factor in determining the Earth's climate. In predicting future warming, it is necessary to understand how atmospheric CO2 has affected past climate change. Past atmosphericCO₂ concentrations have been determined by analyzing gases in ice cores drilled through the Antarctic ice. In this study, we show that the carbon isotope ratios of plant-derived fatty acids in the Bay of Bengal sediments represent past atmospheric CO₂ concentration changes by comparing them with those in ice cores. Using this relationship, we have shown for the first time that atmospheric CO₂ concentration changes before ca 800,000 years ago can be determined with high precision and high temporal resolution. The results show that even before ca 800,000 years ago, the CO₂ concentration fluctuated almost synchronously with the volume of continental ice sheets. However, the CO₂ concentrations were unexpectedly not high during the warm period prior to 1 million years ago. It was also found that the CO₂ concentrations fluctuated earlier than the volumes of continental ice sheets before 1 million years ago but later than the ice volumes after ca 800,000 years ago.