ALKENONES AND POLYCYCLIC AROMATIC HYDROCARBONS RECORD TEMPERATURE AND FIRE IN NORTHEASTERN ALASKAN LAKES

The Arctic is warming twice as fast as the rest of the globe and undergoing shifts in ecological disturbance regimes. These changes threaten to destabilize vast permafrost carbon reservoirs and are potential positive feedbacks to global climate change. To predict the consequences of continued arctic warming we must develop a baseline for past climate variability and its associated feedbacks using proxy records from geological archives. The goal of this research was to develop and apply two lacustrine organic geochemical proxies (alkenones and polycyclic aromatic hydrocarbons) in northeastern Alaska (NE AK) to better understand the region’s climate and fire history.

To develop alkenone paleothermometry in NE AK we applied our new method for alkenone analysis which uses a poly(trifluoropropylmethylsiloxane) stationary phase with gas chromatography-flame ionization detection (GC-FID). The method separated 16 alkenones from NE AK lakes and revealed 4 novel alkenones that went undetected with traditional methods. Analysis of water column particulates revealed that several indices of alkenone unsaturation were well correlated with in situ lake water temperature, allowing for a robust U^K₃₇ temperature calibration (U^K₃₇ = 0.022T-0.764; R² = 0.86; p < 0.01; n = 60). Our application of the calibration to a sediment core from Lake E5, AK (68.38 ^oN, 149.37 ^oE), yielded a 5 kyr early summer water temperature record that shows 2-3 ^oC of variability, slight warming in the last century and general agreement with other arctic records including a recent 2,000 year temperature synthesis [Kaufman, D. S. et al. Recent warming reverses long-term arctic cooling. Science 325,1236–9 (2009)].

Fire records from NE AK are sparse, however recent studies suggest summer temperature is a dominant variable controlling the occurrence and severity of fire in the region. The Anaktuvuk River Fire (68.99 ^oN, 150.28 ^oE) occurred in 2007 and doubled the area burned in the Alaskan arctic tundra for the last 50 years. This major event was recorded by polycyclic aromatic hydrocarbons (PAHs) in the sedimentary record of Dimple Lake, motivating further investigation of the PAH fire proxy in NE AK. Together, alkenones and PAHs compliment traditional proxy records from the region and enhance our understanding of the region’s fire and climate history.