Paleoclimatology of the Paleocene/Eocene using kimberlite-hosted mummified wood from the Canadian Subarctic.

摘要

By the end of this century, if fossil fuel emissions are not reduced atmospheric CO2 will increase to levels that have not existed for tens of millions of years. During the Paleocene/Eocene (P/E) transition (ca. 56--52 Ma), high atmospheric CO2 levels (680--1030 ppmV) caused steeply elevated global temperatures (8 °C higher than modern mean annual temperatures). Arctic and Subarctic regions were warm and humid, supporting a temperate rainforest biome rather than tundra. Although this period has been studied using ocean sediment cores with low temporal resolution, high-resolution proxies (e.g., tree rings) offer the possibility of understanding fine-scale climate variability during the P/E.;Recently, mummified (non-petrified) wood (Taxodioxylon Hartig 1848, and Piceoxylon Gothan 1905) was discovered in Canadian Arctic diamondiferous kimberlites near Lac de Gras, in the Northwest Territories. Wood samples within individual kimberlites were crossdated, to produce some of the oldest floating tree-ring width (RWI) chronologies (up to 417 years in length) in history. Using the oldest verified tree-ring alpha-cellulose ever found (ca. 53.3 Ma), I constructed stable isotope records (d13C and d18O) from samples of Piceoxylon including an 86-year-long record at annual resolution, and a subannual-scale record spanning four tree rings.;Mean temperatures were estimated at 11.4 °C (std. dev. = 1.8 °C), which is an average of 16°C warmer than the modern Subarctic (-4.6 °C). Subannual temperature variation ranged from 3.5--16.4 °C, with a mean of 10.9 °C (std. dev. = 3.0 °C). Spectral analysis of annual records (stable isotope and RWI) exhibited strong bidecadal oscillations (20--30 years/cycle) along with marginally significant interannual, pentadecadal, and centennial oscillations. This oscillatory pattern is similar to the modern Pacific Decadal Oscillation (PDO), suggesting that a PDO-like phenomenon existed in the early Eocene, causing a bidecadal cloudiness regime at our study site, whereby periods of greater cloudiness and increased precipitation caused increased tree growth, alternating with decades of less moisture and decreased tree-ring growth. Results presented here will offer insights into patterns of tree growth and physiological responses to high-CO2 greenhouse climates, providing data with which paleoclimate models of the P/E may be validated.