A 10,000 YEAR RECORD OF ARCTIC TEMPERATURE VARIABILITY DURING THE HOLOCENE INFERRED FROM LIPID BIOMARKERS IN LACUSTRINE SEDIMENTS FROM NORTHERN ALASKA

Current paleoclimate reconstructions from northern Alaska are few in number and do not present a unified pattern of temperature change during the Holocene. Because arctic environments are particularly sensitive to climate forcings and feedbacks, it is necessary to elucidate the effects of past climate forcings in order to fully grasp the implications of rapid anthropogenic climate change in the region. Here we employ two emerging lacustrine organic geochemical proxies (brGDGTs and alkenones) in order to reconstruct a 10,000 year lake surface temperature record using a 3.6m piston core from Lake Fog 2 in northern Alaska. Branched glycerol dialkyl glycerol tetraether lipids (brGDGTs) and long chain alkenones (LCAs) are lipid biomarkers produced by bacteria and haptophyte algae, respectively, and can be used as temperature proxies in lacustrine environments. Because the two proxies record seasonally distinct temperatures, they are sensitive to different climate forcings and when considered together, may present a more comprehensive record of Holocene temperature variability. Our alkenone-based temperature reconstruction indicates that spring lake surface temperatures were warmest in the middle to late Holocene (5.3 to 1.6 Kyr BP), while our summer-biased brGDGT-based temperature record demonstrates that air temperatures were greatest in the early Holocene with a general cooling trend beginning 8 Kyr BP lasting throughout the remainder of the Holocene. Together, the records suggest that while northern Alaska experienced insolation-driven summer cooling, spring/early summer lake temperatures actually warmed into the late Holocene, likely because of changes in atmospheric circulation.