现代环境研究室知识库

In this paper, we present a delta C-13 record that covers the past 750 years at a resolution of 2 - 3 years which was preserved in a precisely dated stalagmite (DY-1) obtained from the Dayu Cave on the south flank of the Qinling Mountains in central China. Between 1249 AD and 1800 AD, climate-induced vegetation changes appear to have been the primary control on delta C-13 values at a centennial scale. Variations in precipitation amounts control the residence time of seepage water and may have affected the dissolution of bedrock, prior carbonate precipitation in the unsaturated zone above the cave, and the degassing of CO2 within the cave. These hydrogeochemical processes are likely to have been the most important controls on delta C-13 levels over annual to decadal scales, and may also have influenced centennial-scale variations. The reduced delta C-13 value of atmospheric CO2 since the Industrial Revolution may have caused the decreasing trend in delta C-13 values seen in stalagmite DY-1 after 1800 AD. Increased visitor numbers in the unventilated Dayu Cave over time produced a large amount of CO2, and maintained a raised level of pCO(2) in the cave air. This artificially enhanced pCO(2) may have decreased the fraction of CO2 degassing, and hence carbonate precipitation, which could partly cause the decreasing trend in the stalagmite delta C-13 seen over the past 200 years.