Climatic and anthropogenic influence on vegetation in southeastern China during the past 120 years inferred from speleothem

Speleothem isotope records have been widely used in the forefront of paleoclimate researches. Although the oxygen isotope (δ¹⁸O) records of speleothems remain the most commonly used hydroclimate proxy, the carbon isotope (δ¹³C) and trace element records of speleothem have also shown their unique advantages in charactering regional-local hydroclimate variations. In this study, we present two high-resolution (seasonal-monthly) and precisely dated speleothem δ¹³C records (NB2 and NB3) over the past 120 years from Niubi cave in Southeast China. Our analyses show that hydroclimate-induced changes in the regional vegetation coverage appear to be the primary control on the speleothem δ¹³C values over the past 120 years. However, during the late 1950s to early 1960s, a large high δ¹³C excursion is observed in the NB record, which is apparently linked to a special human activity in China's modern history, the so-called “Great Leap Forward in Iron and Steel”. We suggest that the large degree of damages to regional vegetation occurred during the time period resulted in the observed high speleothem δ¹³C values, as the local precipitation remained in an ordinary state inferred from δ¹⁸O and trace element data. The persistent decreasing trend in the NB δ¹³C record during the 1980–2018 CE may be attributed to the increased vegetation effect via increases in precipitation, temperature and atmosphere CO₂, as well as the decrease of δ¹³C of atmospheric CO₂.