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

甲烷是一种重要的温室气体，在短期内比二氧化碳更重要。在北极被称为永久冻土的冻土中有很多二氧化碳，随着永久冻土的融化，这些二氧化碳会被释放出来，所以北极的变暖会导致更多的变暖，这是一种所谓的正反馈。了解这种反馈是了解北极系统如何运作的一个重要部分。这一过程大多发生在湖底，其中一些甲烷被冻结在湖底的湖泊沉积物中，但也有一些甲烷来自湖底深处的永久冻土。湖泊下的次永久冻土环境释放的甲烷将是对气候系统的一种新的、尚未得到充分理解的反馈。该项目是在水文-永久冻土-甲烷湖-流域系统中探索这些过程的第一步，为未来的甲烷释放生物地球化学模型提供信息。由于不连续永久冻土地区的湖泊很常见，因此拟议的研究领域将提供适用于整个北极地区的以过程为导向的见解。该项目还将培养博士后、研究生和本科生，并支持一名早期职业科学家。此外，科学教师和他们的学生还将参与湖泊实地考察和课堂活动，并通过国家地理学会的学习计划将结果整合到K-G12课程中，同时还将面向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。大气甲烷（CH4）是热岩溶湖释放的一种重要温室气体，其收支的不确定性限制了气候变化预估的准确性。这项资助的目的是通过整合跨尺度（热岩溶湖到流域）的永久冻土-水文-甲烷过程来完善气候反馈表征。热岩溶湖的甲烷释放通常被认为仅仅来自湖泊及其顶部（湖下的解冻球），而不考虑永久冻土下CH4的产生、储存和潜在逸出。崎岖的永久冻土底部有利于中空“口袋”中的气体储存，当一个开放的通道形成，将永久冻土下层与永久冻土上层连接起来时，可以迅速释放大量的永久冻土下层甲烷。地下水流动可以加速解冻，从而促进CH4的形成和释放。在阿拉斯加内陆的金溪谷，通过实地测量和实验室分析得出的模型实验将验证这样一个假设，即水文-永久冻土-甲烷耦合系统比静态水文和只有超永久冻土CH4源的情景释放更多的CH4。由此产生的辐射强迫将通过概念建模、实地测量和实验室分析进行量化，包括冻土和亚永久冻土层甲烷和二氧化碳的排放、亚永久冻土层甲烷的厌氧氧化以及湖泊沉积物形成泥炭时二氧化碳的吸收和封存。除了流域尺度的量化外，还将为yedoma（富有机物、更新世、以黄土为主的永久冻土带）的泛北极不连续永久冻土带提供次永久冻土带辐射强迫的一级估计。

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).