Annually resolved temperature reconstructions from a late Pliocene-early Pleistocene polar forest on Bylot Island, Canada

Here we use δ¹⁸O ratios measured in tree rings of crossdated sub-fossil wood to reconstruct an annually resolved record of temperature and δ¹⁸O of meteoric water for an interglacial late Pliocene-early Pleistocene fossil forest found on Bylot Island, Nunavut, Canada. Our record represents the first crossdated record of Pliocene wood. Mean annual temperatures determined in this study average -3.4±3.8°C, which is 11.4±4.4°C warmer than present-day Bylot Island (-14.8±2.2°C). June-July temperatures average 13.5±1.1°C, approximately 12.6±1.6°C warmer than present-day. Meteoric water δ¹⁸O values average -15.5±2.9‰, ~2-6‰ more enriched than present values of precipitation δ¹⁸O. Our temperatures are comparable to mid-Pliocene modeled temperatures for the Arctic (3-5°C warmer than present), suggesting that interglacial warm periods in the late Pliocene-early Pleistocene may have been as warm as the mid-Pliocene warm period. That both the Bylot Island forest deposit and the Kap København deposit represent the remains of northern tree-line vegetation that lived during warm interglacial periods within the overall cool Plio-Pleistocene suggests that forest deposits in the Arctic capture a snapshot of interglacial conditions during the Plio-Pleistocene rather than the average Pliocene climate and may not be suitable records to study Pliocene cooling.