Geology

Eocene Arctic Climate

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Science  30 May 2003:
Vol. 300, Issue 5624, pp. 1343
DOI: 10.1126/science.300.5624.1343d

The climate of the Eocene (57.8 to 36.6 million years ago) was so warm that deciduous conifers lived in the Arctic. Despite this warmth, it is unclear what other environmental conditions prevailed to allow coniferous forests to survive through 4 months of continuous daylight during the summer and 4 months of uninterrupted darkness during the winter. Jahren and Sternberg measured the oxygen and hydrogen isotopic compositions of the cellulose from a suite of astoundingly well-preserved fossilized Metasequoia trees that grew 45 million years ago at latitudes of 80°N, near what is now Nunavit, Canada. This allowed them to determine local Eocene atmospheric moisture levels. They also estimated mean annual surface air temperatures by determining the oxygen isotopic composition of secondary carbonates in the fossilized wood. Eocene atmospheric moisture levels were 20 to 120% higher than modern Arctic values, and the mean annual temperature was more than 13°C. These warm temperatures could have increased moisture delivery to high latitudes, and high water vapor levels would have helped to maintain the warmth, particularly through the dark polar winters. These paleotemperatures and relative humidity values are like those of the spring climate of the seasonal rainforests of the North American Pacific Northwest, where relatives of these ancient Metasequoia now grow.—HJS

Geology 31, 463 (2003).

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