A 2500 YEAR LAKE SEDIMENT RECORD OF DROUGHT AND HUMAN ACTIVITY FROM SOUTHWESTERN CHINA

Southwestern China is dominated by monsoon precipitation patterns that have profound implications for modern climate change. Monsoon strength and timing will likely change as a result of changing climate, affecting roughly a billion people who depend on this water source for agriculture. Additionally, this region of China has a long history of human activity including mining, metallurgy, agriculture, and consequent pollution. Here, high-resolution sampling (0.5 cm intervals) of a sediment core from the Yunnan province at Xing Yun Hu (24°10’N, 102°46’E), a drought sensitive lake that behaves as a closed-basin, provides a sub-decadal record of changing climate and human activity in the late Holocene. Specifically, we use bulk sediment carbonate δ¹⁸O and δ¹³C values to document the timing, direction, and magnitude of moisture changes associated with variations in monsoon strength.

On the basis of 6 AMS C¹⁴ dates and Pb²¹⁰ and Cs¹³⁷ dating, the entire core spans 2500 years BP. δ¹⁸O values of authigenic carbonate indicate a wet period persisting from 500 BC to 300 AD. The Medieval Climate Anomaly (MCA) is expressed as a gradual drying period from 300-1200 AD with a brief wet period from 1200-1400 AD. Thereafter, values indicate a rapid transition to a substantially drier climate that takes place over 80 years and persists from 1480-1880 AD as an expression of the Little Ice Age (LIA). δ¹⁸O values return to a slightly wetter climate that continues to present day. Our δ¹⁸O record matches other climate reconstructions that have been performed in the area through speleothem and lacustrine records.

δ¹³C values closely track δ¹⁸O as a good indicator of covariance and closed-basin state until 1600 AD. δ¹³C values then show rapid flux toward a more negative trend into present day. As 1600 AD is the time frame in which many Han immigrants from the north settled and worked land in the Yunnan province, this record has the potential to illuminate the extent of human activity. Combined with other proxies such as C:N ratio and heavy trace metals, we can develop a better understanding of the human and climate interactions in Chinese history.