青藏高原北部典型冰川流域化学风化研究

Chemical weathering in a typical glacier catchment in the northern Qinghai-Tibet Plateau

青藏高原生态环境对气候变化的响应是全球变化研究关注的重点问题。地表风化与气候变化之间具有紧密的联系,因此对冰川流域硅酸盐岩风化以及黄铁矿氧化进行定量研究可为理解高原气候变化提供关键性认识。本文以青藏高原北部祁连山典型冰川流域—老虎沟流域为研究对象,通过分析流域河水及降水的水化学和氢氧同位素,研究了冰川径流来源,河流溶质来源以及水文条件对溶质的影响,流域化学风化速率以及黄铁矿氧化对化学风化碳汇效应的影响。利用同位素径流分割得到地下水、冰川融水以及大气降水对冰川径流的贡献分别为18.2%、58.3%和23.5%,并进一步通过溶质产生模型讨论了冰川河流量对溶质的影响。通过反演模型计算得到碳酸盐岩、硅酸盐岩、蒸发岩和降水对河水阳离子的贡献分别为59.1%、20.1%、8.3%和12.5%,蒸发岩、降水和融雪、黄铁矿对SO^(2-)_(4)的贡献分别为14.4%、8.0%、77.6%。最终估算得到碳酸盐岩和硅酸盐岩的风化通量分别为50.8 g/s和7.8 g/s,相应的CO_(2)吸收速率分别为24.4 t/(km^(2) a)和5.9 t/(km^(2) a)。考虑黄铁矿氧化的影响后,短时间尺度(<106 a)老虎沟流域总CO_(2)吸收速率为8.3 t/(km^(2) a),在长时间尺度(>106 a)则会释放CO_(2),总CO_(2)释放速率为16.2 t/(km^(2) a)。总体来说,本文对老虎沟冰川流域的硅酸盐岩风化以及黄铁矿氧化对气候变化的响应进行了评估,明确了黄铁矿氧化对碳循环的影响,丰富了青藏高原流域风化和碳循环理论研究。

The response of the ecological environment on the Qinghai-Tibet Plateau to global climate change is a crucial topic in global change research.Given the close relationship between surface weathering and climate change,conducting quantitative research on silicate weathering and pyrite oxidation in glacial catchments can provide valuable insights into understanding climate change on the plateau.In this study,we focused on a typical glacial catchment,the Laohugou glacier catchment,located in the Qilian Mountains,north of the Qinghai-Tibet Plateau.Through the analysis of hydrochemistry,water isotopes of the river and precipitation,we explored the sources of glacier runoff,the origin of river solutes,the influence of hydrological conditions on solutes,the rate of chemical weathering in the catchment,and the impact of pyrite oxidation on the carbon sink effect of chemical weathering.Using isotopic hydrograph separation,we found that groundwater,glacial meltwater,and atmospheric precipitation contributed 18.2%,58.3%,and 23.5%,respectively to glacial runoff.By employing a solute production modeling framework,we further examined the influence of discharge changes on the solutes.Additionally,utilizing an inverse model,we estimated the average mass contributions of carbonate,silicate,evaporite,and precipitation to the cations as 59.1%,20.1%,8.3%,and 12.5%,respectively.For SO^(2-)_(4),the contributions of evaporite,precipitation and meltwater,and pyrite were 14.4%,8.0%,and 77.6%,respectively.Finally,we estimated that the weathering fluxes of carbonate rock and silicate rock were 50.8 g/s and 7.8 g/s,respectively,with relative CO_(2) consumption rates of 24.4 t/(km^(2) a)and 5.9 t/(km^(2) a),respectively.As for the impact of pyrite oxidation,the total CO_(2) consumption rate of the Laohugou basin was estimated at 8.3 t/(km^(2) a)in the short term(<106 a),while the total CO_(2) release rate was 16.2 t/(km^(2) a)in the long term(>106 a).Overall,this study provides an evaluation of silicate weathering and pyrite oxidation in the Laohugou glacier catchment under the influence of current climate change.It also sheds light on the impact of pyrite oxidation on the carbon cycle,thereby enhancing our understanding of the weathering and carbon cycle processes on the Qinghai-Tibet Plateau.