Rapid temperature change fractionates gas isotopes in unconsolidated snow, producing a signal that is preserved in trapped air bubbles as the snow forms ice. The fractionation of nitrogen and argon isotopes at the end of the Younger Dryas cold interval, recorded in Greenland ice, demonstrates that warming at this time was abrupt. This warming coincides with the onset of a prominent rise in atmospheric methane concentration, indicating that the climate change was synchronous (within a few decades) over a region of at least hemispheric extent, and providing constraints on previously proposed mechanisms of climate change at this time. The depth of the nitrogen-isotope signal relative to the depth of the climate change recorded in the ice matrix indicates that, during the Younger Dryas, the summit of Greenland was 15 ± 3 °C colder than today.
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We thank W. Broecker for discussions; R. Keeling for prompting our study of thermal diffusion; J. Schwander and R. Francey for reviews; B. Luz for developing the method for analysis of Ar isotopes in air; M. Swanson for the CH4 analyses; J. Orchardo for laboratory assistance; K. Cuffey, G. Clow and J. Schwander for providing pre-publication manuscripts; and the staff of the National Ice Core Laboratory for assistance in ice handling. J.P.S. was supported by a NOAA Climate and Global Change postdoctoral fellowship. We thank US NSF and US DOE (National Institutes of Global Environmental Change) for grant support.
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Severinghaus, J., Sowers, T., Brook, E. et al. Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice. Nature 391, 141–146 (1998). https://doi.org/10.1038/34346
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