Middle Albian climate fluctuation recorded in the carbon isotope composition of terrestrial plant matter

초록

This study presents the carbon isotopic record for terrestrial plant matter (delta C-13(TPM)) in the Jinju Formation, Gyeongsang Basin, Korea, during the middle Albian. The measured delta C-13(TPM) provides continuous high-resolution temporal variations for reconstructing climate change during the middle Albian, which has previously been poorly understood. We found that the delta C-13(TPM) variation mostly exceeds the isotopic variation of the contemporaneous atmospheric CO2, indicating that the variation was primarily governed by climate change rather than atmospheric source. The delta C-13(TPM) values corrected to modern atmospheric CO2 show cyclic fluctuations (-27.8 parts per thousand to -23.3 parts per thousand), reflecting a temporal variation of water availability and/or a related taxonomic turnover of plant communities in the hinterland of Jinju Lake. Based on a transfer function for estimating mean annual rainfall (MAR) from the measured delta C-13(TPM) values, the middle Albian climate of the basin was found to vary from sub-humid to humid conditions (MAR: 500-1500 mm). This variability suggests that Albian climate change at middle latitudes occurred more frequently than previously interpreted. The temporal increase in aridity observed in the basin (35-38 degrees N) has not been detected in the isotopic records of the Cretaceous Hokkaido section (42-45 degrees N) in Japan. This difference implies the possibility of a periodic northward shift or expansion of the northern hemisphere subtropical high pressure belt.

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