Climatic and Anthropogenic Impacts on δ13C Variations in a Stalagmite from Central China


In this paper, we present a δ13C 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 δ13C 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 δ13C levels over annual to decadal scales, and may also have influenced centennial-scale variations. The reduced δ13C value of atmospheric CO2 since the Industrial Revolution may have caused the decreasing trend in δ13C 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 pCO2 in the cave air. This artificially enhanced pCO2 may have decreased the fraction of CO2 degassing, and hence carbonate precipitation, which could partly cause the decreasing trend in the stalagmite δ13C seen over the past 200 years.

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