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This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be...
This is the publisher’s final pdf. The published article is copyrighted by The National Academy of Sciences of the USA and can be found at: http://www.pnas.org/.
To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.