Volcanic and environmental influences of Mt. Fuji on the δ13C of terrestrially-derived n-alkanoic acids in sediment from Lake Yamanaka, central Japan

Abstract The recognition of vegetation changes induced by volcanic eruption is particularly important for paleoenvironmental studies in volcanic regions. In this study, we examined the molecular and stable carbon isotopic compositions (δ 13 C) of sedimentary leaf wax n -alkanoic acids from Lake Yamanaka at the northeastern foot of Mt. Fuji, central Japan, to distinguish volcanic effects on biomarker δ 13 C proxies from other environmental influences over the past 15,000 years. The δ 13 C values of C 30 acids showed a significant positive correlation with average chain length (ACL 24–30 ), suggesting that δ 13 C reflects plant physiological responses to changes in water availability for C 3 plants. The δ 13 C values of C 30 acids showed patterns similar to those of Holocene stalagmite δ 18 O records in Chinese caves, indicating that variations in hydroclimate at the northeastern foot of Mt. Fuji are controlled by large-scale changes in Asian monsoon activity. In contrast, the δ 13 C values of C 24 –C 28 acids increased abruptly at ca. 1750 and 1100 cal yr BP, which coincide with eruptive events at the northeastern flank of Mt. Fuji. This suggests an increase in input from C 4 plants, likely reflecting an increase in C 4 Miscanthus grass, a pioneer species on volcanic deposits, following by the devastation of forest by the eruptions.