Influences of air CO2 on hydrochemistry of drip water and implications for paleoclimate study in a stream-developed cave, SW China  

作　　者：Xiaoxiao Wang Yanhong Wu Licheng Shen 

机构地区：[1]Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China [2]University of Chinese Academy of Sciences, Beijing 100049,China [3]School of Geographical Sciences, Southwest University,Chongqing 400715, China

出　　处：《Acta Geochimica》2016年第2期172-183,共12页地球化学学报（英文）

基　　金：supported by the National Natural Science Foundation of China (NO.41072192);Academician Foundation of Chongqing Science & Technology Commission (CSTC,2010BC7004;CSTC,2013JCYIYS20001)

摘　　要：Cave air CO_2 is a vital part of the cave environment. Most studies about cave air CO_2 variations are performed in caves with no streams; there are few studies to date regarding the relationship of cave air CO_2 variations and drip water hydrochemistry in underground stream–developed caves. To study the relationship of underground stream, drip water, and cave air CO_2, monthly and daily monitoring of air CO_2 and of underground stream and drip water was performed in Xueyu Cave from 2012 to 2013.The results revealed that there was marked seasonal variation of air CO_2 and stream hydrochemistry in the cave. Daily variations of cave air CO_2, and of stream and drip water hydrochemistry, were notable during continuous monitoring.A dilution effect was observed by analyzing hydrochemical variations in underground stream and drip water after rainfall. High cave air CO_2 along with low p H and low δ^(13)C DIC in stream and drip water indicated that air CO_2 was one of the dominant factors controlling stream and drip water hydrochemistry on a daily scale. On a seasonal scale, stream flows may promote increased cave air CO_2 in summer; in turn, the higher cave air CO_2 could inhibit degassing of drip water and make calcite δ^(13)C more negative. Variation of calcite δ^(13)C(precipitated from drip water) was in reverse of monthly temperature, soil CO_2, and cave air CO_2. Therefore,calcite δ^(13)C in Xueyu Cave could be used to determine monthly changes outside the cave. However, considering the different precipitation rate of sediment in different seasons,it was difficult to use stalagmites to reconstruct environmental change on a seasonal scale.Cave air CO2 is a vital part of the cave envi- ronment. Most studies about cave air CO2 variations are performed in caves with no streams; there are few studies to date regarding the relationship of cave air CO2 variations and drip water hydrochemistry in underground stream-de- veloped caves. To study the relationship of underground stream, drip water, and cave air CO2, monthly and daily monitoring of air CO2 and of underground stream and drip water was performed in Xueyu Cave from 2012 to 2013. The results revealed that there was marked seasonal varia- tion of air CO2 and stream hydrochemistry in the cave. Daily variations of cave air CO2, and of stream and drip water hydrochemistry, were notable during continuous monitoring. A dilution effect was observed by analyzing hydrochemical variations in underground stream and drip water after rain- fall. High cave air CO2 along with low pH and low δ13CDIc in stream and drip water indicated that air CO2 was one of the dominant factors controlling stream and drip water hydrochemistry on a daily scale. On a seasonal scale, stream flows may promote increased cave air CO2 in summer; in turn, the higher cave air CO2 could inhibit degassing of drip water and make calcite δ13C more negative. Variation of calcite δ13C （precipitated from drip water） was in reverse of monthly temperature, soil CO2, and cave air CO2. Therefore, calcite δ13C in Xueyu Cave could be used to determine monthly changes outside the cave. However, considering the different precipitation rate of sediment in different seasons, it was difficult to use stalagmites to reconstruct environ- mental change on a seasonal scale.

关 键 词：Carbon dioxide - Underground stream Dripwater Paleoclimate reconstruction Xueyu Cave 

分 类 号：P592[天文地球—地球化学] P532[天文地球—地质学]