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Annual patterns within tree rings of the Arctic middle Eocene (ca. 45 Ma): Isotopic signatures of precipitation, relative humidity, and deciduousness

¹ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
² Department of Biology, University of Miami, Coral Gables, Florida 33124, USA

The spectacular preservation of middle Eocene (ca. 45 Ma) wood allows for intraseason sampling of stable carbon, oxygen, and hydrogen in order to reconstruct the paleoseasonal environment of this Arctic forest (paleolatitude 78.6° ± 1.6° N; present latitude 80° N). Carbon isotopes in bulk organics and cellulose reveal striking annual patterns interpreted as the seasonal switchover from stored to actively acquired carbon associated with deciduous growth in these unusual conifers. Oxygen and hydrogen stable isotopes of cellulose and cellulose nitrate allow for the calculation of changes in relative humidity and in the isotopic value of plant-available water. Clear annual patterns of increasing relative humidity resulting from tissue growth and concomitant transpiration are apparent, as is the systematic increase in the reconstructed oxygen isotope value of environmental water, reflecting progressively increasing temperatures during the growing season.

Key Words: Eocene • Arctic • Metasequoia • relative humidity • deciduousness • tree ring

This article has been cited by other articles:

				J. Eberle, H. Fricke, and J. Humphrey Lower-latitude mammals as year-round residents in Eocene Arctic forests Geology, June 1, 2009; 37(6): 499 - 502. [Abstract] [Full Text] [PDF]