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

Abstract This study presents the carbon isotopic record for terrestrial plant matter (δ13CTPM) in the Jinju Formation, Gyeongsang Basin, Korea, during the middle Albian. The measured δ13CTPM provides continuous high-resolution temporal variations for reconstructing climate change during the middle Albian, which has previously been poorly understood. We found that the δ13CTPM variation mostly exceeds the isotopic variation of the contemporaneous atmospheric CO2, indicating that the variation was primarily governed by climate change rather than the atmospheric source. The δ13CTPM values corrected to modern atmospheric CO2 show cyclic fluctuations (-27.8‰ to -23.3‰), 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 measured δ13CTPM values, the climate of the basin was found to vary from sub-humid to humid conditions (MAR: 500 to 1500 mm) during the middle Albian. 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° N) has not been detected in the isotopic records of the Cretaceous Hokkaido section (42° - 45° N) in Japan. This implies the possibility of a periodic northward shift or expansion of the northern hemisphere subtropical high pressure belt.