Studies of Pliocene climate have in recent years begun to gain more prominence in scientific circles. This is because the Pliocene represents the last period when global temperatures were as warm as future projections predict they will be. One of the most intriguing facets of the Pliocene are the vast numbers of forest sites that have been discovered well north of the modern boreal tree-line. These forest sites contain numerous fossils of flora and fauna with remarkable preservation, affording the opportunity to use multiple proxies to reconstruct climate for this time. This study presents paleotemperature reconstructions using tree-rings and isotopes of fossil wood and mollusks from a well known fossil forest site at Strathcona Fiord on Ellesmere Island. δ¹⁸O, δD, and δ¹³C values of fossil wood indicate a variable climate with alternating intervals of cool/wet to warm/dry weather. These fluctuations may be attributable to phase changes in climate modes. Paleoclimatic modeling of tree isotope values implies growing season temperatures of 11-15 °C (warm month mean), and estimated isotope values of precipitation of –18.3 ‰ (δ¹⁸O) and –228 ‰ (δD). Paleotemperatre estimates derived from δ¹⁸O values from fossil mollusks show comparable temperatures on the order of 12-14 °C (warm month mean) and δ¹⁸O values of peat provide source water estimates of –21 ‰. Both paleotemperature estimates and source water calculations are comparable to those found in a modern Boreal Forest. Time-series spectral analysis was applied to the data, revealing prominent short (<10 years), intermediate (16-35 years) and long-term (~45-50 years) cyclicity, providing evidence for decadal and inter-decadal periodicity in the Pliocene. Preliminary investigations of similar but younger sites from Alaska and Bylot Island indicate similar periodicities suggesting that this is not simply a regional phenomenon.