NOAA/WDS Paleoclimatology - Yukon 17KYr Midge-Inferred July Temperature

The late Quaternary paleoclimate of eastern Beringia has primarily been studied by drawing qualitative inferences from vegetation shifts. To quantitatively reconstruct summer temperatures, we analyzed lake sediments for fossil chironomids, and additionally we analyzed the sediments for fossil pollen and organic carbon content. A comparison with the d18O record from Greenland indicates that the general climatic development of the region throughout the last glaciation–Holocene transition differed from that of the North Atlantic region. Between ~17 and 15 ka, mean July air temperature was on average 5°C colder than modern, albeit a period of near-modern temperature at ~16.5 ka. Total pollen accumulation rates ranged between ~180 and 1200 grains cm-2 yr-1. At ~15 ka, approximately coeval with the Bølling interstadial, temperatures again reached modern values. At ~14 ka, nearly 1000 yr after warming began, Betula pollen percentages increased substantially and mark the transition to shrub-dominated pollen contributors. Chironomid-based inferences suggest no evidence of the Younger Dryas stade and only subtle evidence of an early Holocene thermal maximum, as temperatures from ~15 ka to the late Holocene were relatively stable. The most recognizable climatic oscillation of the Holocene occurred from ~4.5 to 2 ka.