| 英文摘要: | Nontechnical
Methane 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.
Technical
Uncertainties 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). |