天池火山口湖温室气体释放的规模与成因

Caldera lakes of active volcanoes must be regarded as high risk systems that are strongly influenced by volcanic activities such as gas emission, hydrothermal water inflow and rising magma. Quantitative and qualitative study on fluxes and origin of greenhouse gases emitting from caldera lakes has become one of the most effective proxies for monitoring activities of deep-seated magma chamber and forecasting potential future eruptions of active volcanoes, which could also server as important method for evaluating to what extent greenhouse gases released by volcanoes contribute to the atmosphere. The Tianchi caldera lake is the largest caldera lake in China and the deepest mountain lake in the world. Tianchi volcano, although quiescent at present, is undoubtedly the largest and most dangerous active volcano with potential threat of future eruption in China as indicated by the magma chamber beneath the Tianchi volcanic cone and intensive degassing. The exsoluted volcanic gases from the magma chamber can release into the caldera lake, which makes the caldera lake a potential important degassing area for greenhouse gases emission and high risk systems. This proposal will focus on continuous study on fluxes, compositions and origin of greenhouse gases released by Tianchi caldera lake, aiming to quantitatively calculate fluxes of greenhouse at Tianchi caldera lake and reveal genesis of volcanic degassing. Furthermore, the potential links between activities of deep-seated magma chamber and temporal variation of greenhouse gas fluxes and gas compositions will be investigated, which could provide scientific evidence for effectively evaluating activities of deep-seated magma chamber and quantitatively estimating scale of greenhouse gases emitting from Tianchi caldera lake. Our results would be of significant help both for the study of deep carbon cycles and monitoring of volcanic activities.

火山口湖是连接地球深部岩浆和地表水热系统的纽带。对火山口湖温室气体释放通量的测量及其成因的研究已成为当今国际火山学界进行火山活动性监测的有效方法之一，同时也是研究火山区向大气圈释放温室气体规模、进行深部碳循环研究的重要手段。天池是我国最大的火山口湖，火山地下深部存在岩浆囊，湖中存在持续、大量、形式多样的温室气体释放，是潜在的温室气体释放区，也是受火山活动强烈影响的高风险系统。本项目拟综合气体地球化学和水化学的研究方法，在天池火山口湖开展连续的温室气体释放通量测量，进行气体样品和水样品的取样和测试，定量估算天池火山口湖不同类型温室气体释放规模、研究温室气体的来源与成因、探讨火山口湖深部气体的脱气过程，为深部碳循环研究以及火山活动性监测提供科学依据。

火山口湖是连接地表系统和地球深部岩浆‒水热系统的纽带，是探索火山系统内部地质作用的重要窗口，也是地球深部碳循环的重要环节。对火山口湖温室气体（主要是CO2）释放通量的测量及其成因的研究已成为当今国际火山学界进行火山活动性监测的有效方法之一，同时也是研究火山区向大气圈释放温室气体规模、进行深部碳循环研究的重要手段。天池是我国最大的火山口湖，火山深部存在岩浆房，湖中存在持续、大量、形式多样的温室气体释放，是潜在的温室气体释放区，也是受火山活动强烈影响的高风险系统。本项目综合气体地球化学和水化学的研究方法，定量估算了天池火山口湖不同类型温室气体释放规模，对气体的来源与成因以及深部气体的脱气过程进行了系统研究。研究结果表明，1）长白山天池通过水‒气界面扩散向大气中输送的CO2量为3.44×104 t a-1。大量CO2（1.96×105 t）以HCO3-的形式溶解于湖水中，是天池火山口湖中CO2的主要赋存状态。结合火山区干脱气系统温室气体释放通量，初步估算整个长白山天池火山区向大气中输送的CO2量为1.1×106 t a-1，其中，约有28%的CO2来自火山湿脱气系统，火山口湖在深部碳循环研究中具有不可忽视的重要作用；2）He-C同位素示踪结果表明，天池火山气体以幔源为主，表现出壳、幔物质混合的特征。火山区深部岩浆房释放出的深部流体在向上运移过程中与围岩发生相互作用，改变了火山气体的成分以及流体的特征。项目研究获得的上述认识不仅对于准确估算火山来源温室气体的释放规模、进行深部碳循环研究具有重要意义，而且对于深入理解火山口湖气体状态和脱气过程、建立火山口湖未来喷发预测-预警体系以及进行火山活动性监测具有重要的现实意义和科学价值。