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

非技术性甲烷是一种重要的温室气体，在短期内比二氧化碳更重要。在北极的冻土中，有大量的二氧化碳可以随着永久冻土的融化而释放，所以北极变暖可能会导致更多的气候变暖，这就是所谓的积极反馈。理解这样的反馈是理解北极系统如何工作的重要部分。这一过程大部分发生在湖底，一些甲烷冻结在湖下的湖泊沉积物中，但也有一些来自湖下深处的永久冻土之下。从湖泊下的亚多年冻土环境释放甲烷将是对气候系统的一种新的、鲜为人知的反馈。该项目是在水文-多年冻土-甲烷湖-流域系统内探索这些过程的第一步，为未来甲烷释放的生物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，拟议的研究领域将提供适用于整个北极的面向过程的见解。该项目还将培训博士后、研究生和本科生，并支持一名职业生涯早期的科学家。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，并将成果纳入K-G12课程，以及数百万《国家地理》杂志读者、电视观众和K-G12学生。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中心参与，详细了解阿拉斯加的地下水系统。技术上，大气甲烷(CH4)预算的不确定性限制了气候变化预测的准确性。大气甲烷(CH4)是热岩溶湖泊释放的一种重要温室气体。这笔赠款的目的是通过整合不同尺度(从热岩溶-湖泊到分水岭)的永久冻土-水文-甲烷过程来完善气候反馈表述。热岩溶湖泊释放的甲烷通常被认为完全来自湖泊及其塔里克(湖底解冻球茎)，而不考虑永久冻土下甲烷的产生、储存和潜在的逃逸。凹凸不平的永久冻土层底部有利于天然气储存在中空的“口袋”中，当连接次永久冻土和上(上)永久冻土环境的开放的塔利克形成时，可以迅速释放大量次(下)永久冻土CH4储藏。地下水流可以加速融化，从而促进CH4的形成和释放。在阿拉斯加州内陆的Goldstream山谷进行的现场测量和实验室分析提供的模型实验将检验这样一个假设，即耦合的水文-永久冻土-甲烷系统比静态水文和只有超永久冻土CH4来源的情景释放更多的CH4。由此产生的辐射强迫将通过概念模型进行量化，也将由现场测量和实验室分析提供信息，以包括塔里克和亚永久冻土CH4和二氧化碳的排放、亚永久冻土CH4的厌氧氧化，以及随着湖泊沉积物形成泥炭而吸收和封存二氧化碳。除了流域尺度的量化外，还将为泛北极不连续的伊多玛永久冻土区(富含有机质、更新世时代、以黄土为主的永久冻土区)提供次永久冻土层辐射强迫的一阶估计。

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).