OXYGEN ISOTOPE ESTIMATES OF MEAN ANNUAL TEMPERATURE FOR AN EARLY EOCENE, TERRESTRIAL ENVIRONMENT IN THE CANADIAN HIGH ARCTIC

Paleontologic discoveries in the Canadian High Arctic, including fossils of alligators, turtles, and a diversity of mammals, have long implied a mild, temperate Arctic climate during the Eocene. While there are numerous, isotope-based, quantitative data for Tertiary high-latitude marine sediments, data points for high-latitude Arctic terrestrial environments are sparse.  Here we provide quantitative climate estimates for an early Eocene (i.e., late Wasatchian) terrestrial locality on central Ellesmere Island (~79˚N), based upon d¹⁸O_(PO4) analyses of biogenic phosphate in vertebrate teeth and bones. Our climate estimates rely upon an oxygen isotope paleothermometer, developed by others, that utilizes d¹⁸O values of co-occurring mammalian and fish taxa.  The d¹⁸O_(PO4) values from the tooth enamel of two large herbivorous mammals, the hippo-like pantodont, Coryphodon and the tapir Thuliadanta, used with d¹⁸O_(PO4) values from the jaw bone of an Esocid fish (pike), result in estimates of Mean Annual Temperature (MAT) ranging from 9.6 to 12˚ C. Our estimates are several degrees higher than previous estimates by others for early Eocene High Arctic terrestrial environments, and are more compatible with the implied warm-weather vertebrate fauna that inhabited Ellesmere Island at the time.  Furthermore, our MAT estimates compare favorably with recently published Sea Surface Temperatures (SSTs) for the late early Eocene Arctic Ocean.