Climate variability in the Early Pliocene Arctic: Annually resolved evidence from stable isotope values of sub-fossil wood, Ellesmere Island, Canada

Abstract

Tree-ring analyses have contributed significantly to investigations of past climate. Stable isotope climate proxies (δ 18O, δD and δ 13C values) enhance traditional ring-width data, although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the Holocene and the Late Pleistocene. Here we apply stable isotope techniques to wood that represent the remains of Mixed-Coniferous Boreal Vegetation preserved in Early Pliocene (4–5 Ma) deposits at Strathcona Fiord, Ellesmere Island, Canada (ca. 78°N). Four well-preserved tree trunks, identified through wood anatomical characteristics as Larix (larch), from this high Arctic site provide annually resolved sequences of up to 250 years from which we developed a high-resolution record of Pliocene climate. Stable oxygen isotope values, in conjunction with ring-width measurements were used to derive annually resolved temperature records for this site. Our ring-width and isotope-based reconstructions provide an annually resolved record, up to 250 years, of temperature and indicate growing season (JJ) temperatures (15.8 ± 5.0 °C) 11.8 ± 5.1 °C, and mean annual temperatures (MAT) (− 1.4 ± 4.0 °C) 18.3 ± 4.1 °C warmer than present. Estimated isotope values of precipitation of − 16.3 ± 2‰ (δ 18O) and − 150.1 ± 8.9‰ (δD) were calculated from the isotopic values of wood cellulose. Relative humidity estimated from both δ 13C and δD records ranged from 60 to 80%. Paleotemperature, source water and humidity estimates are comparable to those of a modern Boreal Forest growing ca. 15–20° south of modern Ellesmere Island.