Tracing paleo-permafrost with meteoric 10Be and in-situ 26Al/10Be - A proof of concept

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Determining the past thermal regime of thick carbon-bearing permafrost soil blanketing northeastern Siberia is critical for understanding Plio-Pleistocene carbon sequestration, longterm climate cooling and constraining the potential for release of this pool of stored carbon in the future. This project will develop and apply a novel meteoric Beryllium-10 (10Be) technique in concert with the in-situ Aluminum-26/Beryllium-10 (26Al/10Be) chronometer in order to determine the thermal history of permafrost within the El’gygytgyn impact crater in the Siberian Arctic from time of the mid-Pliocene impact to today. The results will provide not only a chronology within the lower parts of the 141 m core drilled in 2008 where no other age control exists, but will also allow a better understanding of the rate and style of frozen ground build-up by using a recently developed isochron method for interpreting 26Al/10Be ratios in sediments. Here, we attempt to use a known geochemical tracer in a new way, which provides a record of the thermal regime of the soil from precipitation-derived (meteoric) 10Be. When frozen, soil does not build up meteoric 10Be; when thawed, 10Be migrates through the active layer. Our research will investigate the use of this isotope tracer for determining the relative duration soils have experienced thawed conditions since deposition. This information, when linked with climate proxies from the Lake El’gygytgyn cores, will yield key connections between past temperatures and depth of permafrost thaw and to provide realistic constraints on the impact of past warm and cold episodes on permafrost generation and maintenance in the context of anticipated global warming. The method can be extended to other Arctic terrains to determine the history and fate of other carbon reservoirs.