Methane release from thermokarst lakes: Thresholds and feedbacks in the lake to watershed hydrology-permafrost system

热岩溶湖泊的甲烷释放：湖泊对流域水文-永久冻土系统的阈值和反馈

• 批准号: 1500931
• 负责人: Anna Liljedahl
• 金额: $ 208.68万
• 依托单位: University of Alaska Fairbanks Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1500931&HistoricalAwards=false
• 关键词: Methane; release; thermokarst; lakes; Thresholds

NontechnicalMethane is an important greenhouse gas, much more so than carbon dioxide over the short term. There is a lot of it in frozen ground, called permafrost, in the Arctic that can be released as the permafrost thaws, so warming in the Arctic can lead to more warming, a so-called positive feedback. Understanding such feedbacks is an important part of understanding how the arctic system works. Much of this process occurs at the bottoms of lakes, where some of the methane is frozen in lake sediments beneath the lake, but some also comes from under the permafrost deep under the lake. Methane release from the sub-permafrost environment under lakes would be a new and poorly understood feedback to the climate system.This project is a first step in exploring these processes within the hydrology-permafrost-methane lake-to-watershed system to inform future biogeochemical models for methane release. Since lakes in areas of discontinuous permafrost are common, the proposed study domain will offer process-oriented insights that are applicable across the Arctic.The project will also train postdocs, graduate and undergraduate students and support an early-career scientist. In addition there will be outreach to science teachers and their students in fieldwork and classroom activities on lakes and integration of results into K-G12 curriculum through the National Geographic Society's Learning program, and to millions of National Geographic magazine readers, television viewers and K- G12 students. Further, the efforts will contribute to the Alaska Geological and Hydrological Survey program to develop a detailed understanding of Alaska's groundwater systems via the central involvement of the Alaska Geological and Geophysical Survey.TechnicalUncertainties in the budget of atmospheric methane (CH4), an important greenhouse gas released by thermokarst lakes, limit the accuracy of climate change projections. The objective of this grant is to refine climate feedback representations by integrating permafrost-hydrology-methane processes across scales (thermokarst-lake to watershed). Methane release from thermokarst lakes is typically considered to be solely derived from the lake and its talik (thaw bulb beneath the lake), while not accounting for the production, storage, and potential escape of CH4 beneath the permafrost. A rugged permafrost bottom is proposed to favor gas storage in hollow "pockets", which can rapidly release large sub(below)- permafrost CH4 stores when an open-talik forms that connects the sub-permafrost to the supra(above)- permafrost environment. Groundwater flow could accelerate thaw and therefore enhance CH4 formation and release. Model experiments informed by field measurements and laboratory analyses at Goldstream Valley, Interior Alaska, will test the hypothesis that the coupled hydrology-permafrost-methane system releases more CH4 than a scenario with static hydrology and only supra-permafrost CH4 sources. The resulting radiative forcing will be quantified via conceptual modeling, also informed by field measurements and laboratory analyses, to include talik and sub-permafrost CH4 and CO2 emissions, anaerobic oxidation of sub-permafrost CH4, and CO2 uptake and sequestration as lake sediments form peat. In addition to a watershed-scale quantification, a first order estimation of the sub-permafrost derived radiative forcing will be provided for the pan-arctic discontinuous permafrost domain of yedoma (organic-rich, Pleistocene-aged, loess-dominated permafrost).

甲烷是一种重要的温室气体，在短期内比二氧化碳更重要。在北极的冻土层中有很多二氧化碳，这些二氧化碳可以随着冻土层的融化而释放出来，所以北极的变暖会导致更多的变暖，这就是所谓的正反馈。了解这种反馈是了解北极系统如何运作的重要组成部分。这一过程大部分发生在湖底，其中一些甲烷被冻结在湖底的沉积物中，但也有一些来自湖底深处的永久冻土。湖泊下的亚冻土环境中的甲烷释放将是一个新的和知之甚少的气候系统的反馈。该项目是在水文-冻土-甲烷湖泊-流域系统中探索这些过程的第一步，为未来的甲烷释放地球化学模型提供信息。由于不连续永久冻土区的湖泊很常见，因此拟议的研究领域将提供适用于整个北极的过程导向的见解。该项目还将培训博士后，研究生和本科生，并支持早期职业科学家。此外，还将通过国家地理学会的学习计划，向科学教师及其学生提供关于湖泊的实地考察和课堂活动，并将结果纳入K-G12课程，并向数百万国家地理杂志读者，电视观众和K-G12学生提供服务。此外，这些努力将有助于阿拉斯加地质和水文调查计划，通过阿拉斯加地质和地球物理调查的主要参与，详细了解阿拉斯加的地下水系统。该赠款的目的是通过整合不同尺度（热岩溶湖到流域）的冻土-水文-甲烷过程来完善气候反馈表示。热岩溶湖泊的甲烷释放通常被认为是完全来自湖泊及其talik（湖下的解冻球），而不考虑永久冻土下CH 4的生产，储存和潜在的逃逸。一个崎岖的永久冻土底部，建议有利于气体存储在中空的“口袋”，它可以迅速释放大的子（下）-永久冻土CH 4商店时，一个开放的talik的形式，连接子永久冻土上（上）-永久冻土环境。地下水流动可以加速解冻，从而增加CH 4的形成和释放。在Goldstream山谷，阿拉斯加内陆的实地测量和实验室分析的模型实验，将测试的假设，耦合水文永久冻土甲烷系统释放更多的甲烷比静态水文和只有超永久冻土甲烷源的情况。由此产生的辐射强迫将通过概念模型进行量化，也通过实地测量和实验室分析，包括talik和亚永冻土甲烷和二氧化碳排放量，亚永冻土甲烷的厌氧氧化，以及二氧化碳吸收和封存湖泊沉积物形成泥炭。除了一个流域尺度的量化，一阶估计的亚永久冻土衍生辐射强迫将提供泛北极不连续的永久冻土域的yedoma（有机丰富，更新世年龄，黄土为主的永久冻土）。