Cosmogenic nuclide enhancement via deposition from long-period comets as a test of the Younger Dryas impact hypothesis

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We explore the idea that detectable excursions in 26Al may arise from direct deposition by any bolide, and excursions in 14C and 10Be abundances in the atmosphere may result from long-period comet impacts. This is very different from the usual processes of production by cosmic rays within Earthʼs atmosphere. Long-period comets experience greatly increased cosmic ray flux beyond the protection of the sunʼs magnetic field. We report the computed amount of 14C, 10Be, and 26Al present on long-period comets as a function of comet mass. We find that the amount of nuclide mass on large long-period comets entering the Earthʼs atmosphere may be sufficient for creating anomalies in the records of 14C and 10Be from past impacts. In particular, the estimated mass of the proposed Younger Dryas comet is consistent with its having deposited sufficient isotopes to account for recorded 14C and 10Be increases at that time. The 26Al/10Be ratio is much larger in extraterrestrial objects than in the atmosphere, and so, we note that measuring this ratio in ice cores is a suitable definitive test for the Younger Dryas impact hypothesis, even if the hypothetical bolide is not a long-period comet and/or did not contribute to the 14C and 10Be increases.