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The influence of hydrogeology and carbon sources on speleothem δ13C based on long-term monitoring in Furong Cave, southwest China
Chemical Geology ( IF 3.6 ) Pub Date : 2024-06-07 , DOI: 10.1016/j.chemgeo.2024.122210 Jun-Yun Li , Ting-Yong Li , Hong-Chun Li , Christoph Spötl , Chao-Jun Chen , Jian Zhang , Yao Wu , Hua-Yan Li , Yue Jin , Min Zhao , Hong-Kai Li , Yan-Min Dong
Chemical Geology ( IF 3.6 ) Pub Date : 2024-06-07 , DOI: 10.1016/j.chemgeo.2024.122210 Jun-Yun Li , Ting-Yong Li , Hong-Chun Li , Christoph Spötl , Chao-Jun Chen , Jian Zhang , Yao Wu , Hua-Yan Li , Yue Jin , Min Zhao , Hong-Kai Li , Yan-Min Dong
The stable carbon isotopic composition of speleothems is an important but incompletely understood parameter in paleoclimatological and paleoenvironmental reconstruction, recording changes in vegetation and hydrology. This study systematically assesses the influences of karst hydrology, cave environment, and carbon sources on the δC values of farmed calcite in Furong Cave, located in Chongqing, southwest China. Six drip sites (MP1-MP5) were monitored between 2009 and 2019, and ΔC data (ΔC is the difference in the C/C ratio between a sample and a standard, expressed in permille, ‰) of soil organic matter, drip water and farmed calcite (calcite precipitated on a glass substrate) were obtained. A linear relationship was found between the seasonal variability of CO in cave air and δC of the farmed calcite in “Great Hall” characterised by a relatively stable microenvironment. The growth rate and δC values of the farmed calcite was not be affected by the drip rate unless the drip rate decreased to <1 drip/min for a long time, leading to a decrease in growth rate and higher δC values because of longer CO degassing. MP2 and MP9 show faster drip rates, higher δC and lower ΔC than MP1 and MP3, which suggests that the “old carbon” in MP9 is derived from the host rock. MP4 and MP5 are characterised by slower drip rates and lower δC and δC, and the ΔC values of the farmed calcite are lower than those of MP9. The slow drip rate indicates that less infiltration water reaches MP4 and MP5, and soil CO derived from the decomposition of “old” organic matter enters the fractures that lead to these drip sites. The fast drip rate of MP9 suggests that the fissures feeding this drip site are mostly water-saturated, limiting the exchange between soil CO and CO and allowing more “old carbon” from the bedrock to dissolve leading to higher δC. This study emphasizes that in addition to changes in the cave environment, the source(s) of the carbon may be a more important factor controlling the δC values of drip water (and speleothem) than drip rate.
更新日期：2024-06-07
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