| Summary: | Cellulose is resistant to degradation on geologic timescales and provides a reliable record of the oxygen isotope composition of meteoric water (δ18OMW). A strong empirical relationship between the δ18OMW value and temperature has been observed in modern settings, allowing researchers to reconstruct mean annual temperature via measurements of the δ18O value of cellulose (δ18Ocell). I present high-resolution intra-annual δ18Ocell measurements across fossil growth rings in mummified wood collected from late Pleistocene sediments (∼50,000 to 44,000 14C BP) within the Yedoma Silt Ice Complex at Duvanny Yar in far northeastern Siberia. These data are used to quantify year-to-year changes in seasonal temperatures at the site, including warm and cold month mean temperatures (Tmax and Tmin, respectively). Results suggest Tmax = 6.4 ± 3.0 °C (average ± 1σ) and Tmin = -37.7 ± 2.9 °C during the late Pleistocene, which is significantly (Tmax p = 0.0005, Tmin p = 0.05) colder than today’s values (modern: Tmax = 13.2 ± 2.1 °C, Tmin = -34.8 ± 2.6 °C). Assuming a normal distribution for monthly temperatures similar to modern continental climates, I calculate that above-freezing mean monthly temperatures occurred in ~1.6 fewer months during the late Pleistocene than today. These cold conditions allowed for the Arctic to act as a significant carbon sink during the late Pleistocene, despite shorter growing seasons as compared to today. Extrapolation to current Arctic warming suggests that increased temperatures will allow for longer periods of net carbon release from Arctic soils each summer, despite increased photosynthesis.
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