The proposed work will test whether the onset of the Younger Dryas (about 12,900 years ago) was caused by a cometary impact over the Laurentide Ice Sheet. In particular, the team will seek to determine 1) whether the magnetic properties of iron spherules found at the based of the Younger Dryas at many sites are consistent with formation from a cometary impact, 2) whether evidence for ejecta from the impact event can be found in lacustrine sequences in the western United States where the Younger Dryas boundary is already known to be present but where evidence for an impact has not yet been sought, and 3) whether a dark layer at the base of unit in Europe that has correlated with the Younger Dryas contains material that would be consistent with the hypothesis.
Scientific Merit: There is enough physical evidence for an impact at the onset of the Younger Dryas that careful additional work seems warranted. If the hypothesis is correct, it will produce such a fundamental change in our understanding of the causes of abrupt climate change.
Broader Implications: The causes and consequences of large-scale, global climatic change are still not well-understood. Finding a new mechanism for an important, recent, global climate event will significantly advance our knowledge of the processes that drive climatic variations. It will also provide fundamental insights into how modern climatic variations will be affected by similar processes.
