ARCTIC CLIMATIC RECONSTRUCTION USING A PLIOCENE FOREST DEPOSIT, ELLESMERE ISLAND, CANADA

The Pliocene epoch is the most recent geologic epoch that provides a strong analog for climate that is anticipated for the end of this century. The main driver of contemporary climate warming is increased CO₂ in the atmosphere. We have reached levels of pCO₂ that existed in the Pliocene and are thus likely to reach temperatures similar to that epoch soon. Pliocene aged sediment deposits can be used as proxies for environmental conditions that are anticipated for our near future.

The most northerly known mummified forest in North America was discovered next to the Ad Astra ice cap, Ellesmere Island, Canada (81.7° N) in 2009. Materials were recovered from this site during 2009, 2010, and 2016. We have assigned a Pliocene age for these remains based on the macrofossil assemblage that is present, ¹⁴C dating, and the absence of diagnostic fossils that would indicate an older age for the deposit. A comparison of the fossil assemblages from this site to other circumpolar fossil forest sites indicates that the greatest similarity is to the Fyles Leaf Bed and Beaver Pond sites (Ellesmere Island), that have been determined to be Pliocene in age.

The forest remains at this site have not been lithified, which permits high resolution dendrochronolic analysis. The ring widths of 17 tree trunks collected during 2010 and 2016 were measured, producing a mean ring width of 461.97 μm (range: 86.86 μm to 837 μm). Temperature estimates were made by measuring the δ¹⁸O of α-cellulose that was extracted at annual and decadal time intervals from mummified tree trunks. The δ¹⁸O suggests mean annual temperature of -10.82°C, approximately 8.0°C warmer than near this deposit in present day and 4.3°C cooler than the mean annual temperature at the current tree line south of the site. The results presented here add to the existing database for Pliocene Arctic climate and extends late-Pliocene treeline 365km north from Beaver Pond and 2630km north of current tree line. The temperature reconstruction suggests that this deposit is mid to late Pliocene in age and indicates that climate was likely entering Plio-Pleistocene cooling.