ELLESMERE ISLAND AS AN ARCTIC COUNTERPOINT TO THE MID-LATITUDES: ISOTOPIC SIMILARITIES, DIFFERENCES, AND THEIR RELEVANCE TO PALEOENVIRONMENTAL RESEARCH

Paleogene deposits are relatively common in mid-latitudes of western North America, but are less common in other regions, particularly above the Arctic Circle. Nevertheless such deposits can provide important points of comparison with mid-latitude sites, both for the study of environmental and ecological gradients and possible changes in these gradients over time. Here, we review stable isotope results obtained from vertebrates from Early Eocene (late Wasatchian) strata on central Ellesmere Island (~79˚N). These include the pantodont Coryphodon and the perissodactyls Thuliadanta (tapiroid) and cf. Eotitanops (brontothere), as well as fish. These data are compared to isotopic data from approximately coeval representatives of the same (or similar) taxa – Coryphodon, Heptodon (tapiroid), Eotitanops, Lambdotherium (brontotheres) and gar from mid-latitude sites in Wyoming and Colorado.

In the case of stable carbon isotopes, lower d¹³C values of Arctic Coryphodon (-10.8 to -12.8 ‰), compared to Arctic tapir and brontothere (-7.8 to -9.4 ‰), reflect dietary and habitat differences that are consistent with a preference by Coryphodon for a more closed-canopy, riparian environment. Similar offsets in carbon values were observed between mid-latitude Coryphodon (~ -11 to -14 ‰) and the perissodactyls Heptodon, Eotitanops, and Lambdotherium (~ -9 to -12 ‰), suggesting that similar habitat differences among taxa existed regardless of latitude. Documentation of behavioral consistency such as this helps constrain interpretations of mammalian carbon isotope data from all Paleogene deposits. Higher carbon isotope ratios for all high-latitude mammals compared to mid-latitudes likely reflects differences in vegetation and seems consistent with prevalence of conifer forests in the Eocene High Arctic.

In the case of oxygen isotope ratios, paired data from fish and mammals (Coryphodon and Thuliadanta) indicate that MAT was ~9 to 12 ºC for the Early Eocene High Arctic. Isotope ratios for Arctic mammalian taxa are ~9 to 11 ‰ lower than those from mid latitudes, indicating shallower temperature gradients and increased water vapor transport to high latitudes at this time compared to today. Both of these paleoclimatic features probably facilitated dispersal of plants and animals over North America during the Early Eocene.