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A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

机译：全新世时期热喀斯特湖从碳源到汇的转变

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摘要

随着全新世时期气候开始变暖,永久冻土退化在西伯利亚、阿拉斯加和加拿大北部大面积地区产生了无数的热喀斯特湖(当融水在消融的永久冻土上的表面凹陷中积累时所形成的湖泊)。由于有机物降解,这些湖泊被普遍认为是大气甲烷和二氧化碳的一个净来源。但问题是,这些湖泊以有机物积累的形式所吸收的碳是否能抵消温室气体排放？这项研究发现,深层热喀斯特湖沉积物中的碳积累使对永久冻土地区的环北极泥炭碳储量的估计值增加一半以上,大于当这些湖泊首次形成时由更新世时期的永久冻土作为温室气体所释放出的碳的量。作者提出,热喀斯特盆地在距今大约5,000年前从净辐射变暖气候效应变成了净变冷气候效应。%Thermokarst lakes formed across vast regions ot Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 peta-grams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.
机译：随着全新世时期气候开始变暖,永久冻土退化在西伯利亚、阿拉斯加和加拿大北部大面积地区产生了无数的热喀斯特湖(当融水在消融的永久冻土上的表面凹陷中积累时所形成的湖泊)。由于有机物降解,这些湖泊被普遍认为是大气甲烷和二氧化碳的一个净来源。但问题是,这些湖泊以有机物积累的形式所吸收的碳是否能抵消温室气体排放？这项研究发现,深层热喀斯特湖沉积物中的碳积累使对永久冻土地区的环北极泥炭碳储量的估计值增加一半以上,大于当这些湖泊首次形成时由更新世时期的永久冻土作为温室气体所释放出的碳的量。作者提出,热喀斯特盆地在距今大约5,000年前从净辐射变暖气候效应变成了净变冷气候效应。%Thermokarst lakes formed across vast regions ot Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene carbon accumulation in 20 lake sediments (47 ± 10 grams of carbon per square metre per year; mean ± standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 peta-grams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.

著录项

  • 来源
    《Nature》 |2014年第7510期|452-456b1|共6页
  • 作者

    K. M. Walter Anthony; S. A. Zimov; G. Grosse; M. C. Jones; P. M. Anthony; F. S. Chapin Ⅲ; J. C. Finlay; M. C. Mack; S. Davydov; P. Frenzel; S. Frolking;

  • 作者单位

    Water and Environmental Research Center, University of Alaska, Fairbanks, Alaska 99775-5860, USA;

    Northeast Scientific Station, Pacific Institute for Geography, Far-East Branch, Russian Academy of Sciences, Cherskii 678830, Russia;

    Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775-7320, USA,Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam 14473, Germany;

    Water and Environmental Research Center, University of Alaska, Fairbanks, Alaska 99775-5860, USA,US Geological Survey, Reston, Virginia 20192, USA;

    Water and Environmental Research Center, University of Alaska, Fairbanks, Alaska 99775-5860, USA;

    Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775-7000, USA;

    Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, Minnesota 55108, USA;

    Departmentof Biology, University of Florida, Gainesville, Florida 32611, USA;

    Northeast Scientific Station, Pacific Institute for Geography, Far-East Branch, Russian Academy of Sciences, Cherskii 678830, Russia;

    Max Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany;

    Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824-3525, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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