Temperature dominates leaf wax n-alkane carbon isotope composition of terrestrial C3 angiosperms in humid zones

Abstract

The C3 plant leaf wax δ13C (δ13Calk) is commonly used to reconstruct past climates. However, our understanding of how precipitation and temperature influence terrestrial C3 δ13Calk is limited. To address this gap, we investigated the δ13C of n-C29 alkane (δ13C29) of C3 terrestrial angiosperms in subtropical humid regions in China and compiled a global dataset. Results show a strong correlation between C3 terrestrial angiosperms δ13C29 and mean annual temperature in both Chinese subtropical humid regions (r = −0.94, p < 0.001) and global humid zones (r = −0.78, p < 0.001). The linear fit lines of the regional and global datasets have similar slopes (−0.3129 vs −0.2896) and intercepts (−30.82 vs −31.41), indicating consistent responses to air temperature in global humid zones. When considering only sites with temperature data from meteorological stations, the correlation coefficient increases to −0.96 (p < 0.001) for the global dataset. In contrast to humid zones, mean annual precipitation significantly correlates with C3 terrestrial angiosperms δ13C29 in arid zones (r = −0.75, p < 0.001), supporting the main controls of precipitation in these areas. These findings emphasize the impact of temperature on C3 terrestrial δ13Calk, particularly in humid zones, and highlight caution when interpreting δ13Calk in geological records under changing hydroclimate conditions or unstable settings.