A 50,000-YEAR-LONG ARCTIC PALEOCLIMATE RECORD FROM A LOESS-PALEOSOL SEQUENCE, KOTZEBUE, ALASKA, USA

One of the most remarkable findings of the past two decades has been the discovery of multiple periods of interstadial warming alternating with stadial cooling in Greenland. These events occurred between the time of the last interglacial period (~120 ka) and the last glacial maximum (~20 ka). The interstadial warming and stadial cooling cycles have estimated temperature amplitudes that are roughly half that of a full interglacial-glacial cycle in Greenland. If the warm interstadial periods were of pan-Arctic extent, there should be geologic records of them in other parts of the Northern Hemisphere. This hypothesis was tested by examination of loess records in Arctic Alaska. Near Kotzebue, 8.5 m of loess deposits overlie ~2 m of lacustrine sediments. Optically stimulated luminescence (OSL) geochronology indicates ~50,000 years of periods of loess accretion (glacial periods) alternating with times of landscape stability and soil formation (interstadial periods), between ~39 ka and ~90 ka. Mineralogy and trace element geochemistry permit an interpretation that during cold stadials, silts could have been derived from expanded glacial sources in the Brooks Range and the Delong and Schwatka Mountains, subsequently transported via tributaries to the Noatak and Kobuk Rivers and finally entrained by wind and transported to Kotzebue to accumulate as loess. Six paleosols are identified by darker colors, higher organic matter content, higher clay content, and higher values of both total and plant-available phosphorus. Although unaltered loess contains calcite, this mineral has been leached from the paleosols. Thus, during warm interstadials, the landscape around Kotzebue was likely stabilized by an acidic vegetation (moist, shrub tundra?) and soil formation occurred. Five of the loess-paleosol couplets formed between 66 ± 8 ka and 90 ± 11 ka, based on OSL ages. These loess-paleosol couplets could therefore correlate with the earliest part of the interstadial-stadial record of Greenland and imply that rapid warming-cooling episodes were widespread across the Arctic.