The influence of hydrogeology and carbon sources on speleothem δ13C based on long-term monitoring in Furong Cave, southwest China
Journal
Chemical Geology
Journal Volume
662
Start Page
122210
ISSN
0009-2541
Date Issued
2024-09
Author(s)
Li, Jun-Yun
Li, Ting-Yong
Spötl, Christoph
Chen, Chao-Jun
Zhang, Jian
Wu, Yao
Li, Hua-Yan
Jin, Yue
Zhao, Min
Li, Hong-Kai
Dong, Yan-Min
Abstract
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 δ13C values of farmed calcite in Furong Cave, located in Chongqing, southwest China. Six drip sites (MP1-MP5) were monitored between 2009 and 2019, and Δ14C data (Δ14C is the difference in the 14C/12C 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 pCO2 in cave air and δ13CCc of the farmed calcite in “Great Hall” characterised by a relatively stable microenvironment. The growth rate and δ13CCc 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 δ13CCc values because of longer CO2 degassing. MP2 and MP9 show faster drip rates, higher δ13CDIC and lower Δ14C 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 δ13CDIC and δ13CCc, and the Δ14C 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 CO2 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 CO2 and CO32− and allowing more “old carbon” from the bedrock to dissolve leading to higher δ13CDIC. 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 δ13C values of drip water (and speleothem) than drip rate.
Subjects
Carbon sources
Cave monitoring
Hydrogeology
Karst
Radiocarbon
Stable carbon isotopes
SDGs
Publisher
Elsevier BV
Type
journal article