A NEW HIGH-RESOLUTION STABLE ISOTOPE RECORD FROM PLIOCENE WOOD, ELLESMERE ISLAND, NUNAVUT, CANADA

The Canadian Arctic is a region known to be highly sensitive to changes in climate. The Cenozoic fossil record documents evolution of polar vegetation in response to global climate deterioration, with continuous forest cover and an absence of a northern treeline until the close of the Tertiary. Terrestrial climate records for the region have most commonly been based on NLR (nearest living relative) and physiognomic studies of the flora and fauna. These methods provide low-resolution records over broad regions, leaving unresolved certain key questions.

Strathcona Fiord, at 79°N on Ellesmere Island, Canadian High Arctic, is the source of a rich Pliocene (4-2.5 Ma) biota.  A mixed coniferous-deciduous vegetation, with a diverse mammal fauna including beavers, shrews, badgers and bears, resembles the extant cool-temperate boreal forests of Canada. The excellent preservation of wood recovered from the Strathcona Fiord site provides an opportunity to obtain a quantitative secular record of Arctic climate from stable isotope studies of tree-rings.

Extraction of d¹⁸O, d¹³C and dD isotope ratios from wood cellulose has proven to be a valuable method for the interpretation of palaeoclimate; however, sample preservation has generally limited these methods to Holocene woods. This study represents the first high-resolution secular isotope study of Pliocene wood, with a consecutive annual record of climate over a period of more than 100 years. Data obtained from the oxygen and carbon isotopes show highly variable climate with long periods of cool dry conditions and shorter periods of warm wet conditions and a brief 4 year cyclicity early in the record. Ongoing analysis of the hydrogen isotopes will provide us with additional information about precipitation as well as the possibility of discerning precise annual temperatures. Our study will provide insight into the changes that brought an end to the vast forests that once covered the polar regions.