mental water was strikingly depleted in heavy O isotopes. In modern ecosystems, such ratios would indicate annual average temperatures below 0 C. However, the authors reject such cold paleotemperatures to explain the data because the lush forests could not have grown at these temperatures. Instead, they suggest that global-scale weather patterns were different: Moisture was progressively depleted in heavy oxygen isotopes as it traveled from low latitudes in the Pacific ocean across North America. These air circulation patterns delivered both warm air and isotopically depleted moisture to the Arctic during the summer months of continuous sunlight and explosive growth. Such a weather pattern, with no Arctic Front as we have today, is radically different from weather patterns thought to be in place before and after the Eocene and may partially account for the abundance of vegetation at high latitudes during the Eocene relative to any other period in Earths history.

* A. Hope Jahren, Assistant Professor of Geobiology and Climatology at the Department of Earth and Planetary Sciences, Johns Hopkins University, was awarded the GSA Young Scientist Award (Donath Medal) for 2001. The Young Scientist Award was established in 1988 to be awarded to a young scientist (35 or younger during the year in which the award is to be presented) for outstanding achievement in contributing to geologic knowledge through original research that marks a major advance in the earth sciences. The award, consisting of a gold medal and a cash prize, was endowed by Dr. and Mrs. Fred A. Donath.

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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
4-Jan-2002

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