MIDDLE EOCENE (~45 MA) PALEOCLIMATE INFERRED FROM FOSSIL TREE CELLULOSE

Paleoclimate interpretations using the established correlation between d¹⁸O and dD values in tree cellulose and environmental temperature have been restricted to recent and Quaternary application due to the lack of sufficiently preserved cellulose in older tree fossils. A striking exception to this is the middle Eocene (~45 Ma) fossil forest of Axel Heiberg Island, which contains abundant stumps, branches, twigs, cones and leaves of Metasequoia trees in exquisite preservational condition. These deciduous trees grew at a paleolatitude of 80 degrees North, and endured prolonged periods of continuous daylight in the summer and continuous darkness in the winter, making the ecosystem completely unlike any forest community existing today. Fossil wood samples from the site have been slightly compressed, but otherwise exhibit minimal alteration: %C and % cellulose (by mass) are similar to modern Metasequoia wood.

I report on d¹⁸O and dD values gained from unusually old tree fossils, collected on Axel Heiberg Island of the Canadian High Arctic. 16 Metasequoia individuals were analyzed in duplicate; mean d¹⁸O value=19.9 % (range=17.1 to 22.2 %; variability within an individual=0.5 %). Paleotemperature prediction based on Cellulose d¹⁸O value vs. MAT ( after the relationship in Epstein et al., 1977) yields a predicted MAT=-2.7 degrees C (+/- 2.5); the site's current MAT=-19.6 degrees C. A Latitude climate similarity estimate based on d¹⁸O of Environmental Water vs. Latitude (after the relationship in Rozanski et al., 1993) yields a predicted latitude similarity=71.4 degrees N (+/- 4.3), similar to the current position of Tromsø, Norway (MAT=2.9 degrees C). Both lines of reasoning lead to scenarios much warmer than current conditions at the site, but comparable to the coldest inhabited cities on the planet today -- considerably cooler climate than has been suggested for the middle Eocene. In presentation, we will complement these results with dD determinations on cellulose nitrate isolated from the same individuals, as well as d¹⁸O and dD values of small plants presently growing in the arctic.