δ18O and δD suggest episodic Late Pleistocene ice wedge growth in Central Alaska

Stable isotopes in ancient buried ice wedges from the Cold Regions Research and Engineering Laboratory Permafrost Tunnel indicate growth occurred during three cold episodes during the Late Pleistocene in Central Alaska. Oxygen (δ¹⁸O) and hydrogen (δD) stable isotopes were analyzed at high resolution in seven ice wedges (1N, 14.9SWinze, 18N, 35S, 45S, 52.5S, and 58N). Three stratigraphically separate climatic events are apparent in the δ¹⁸O, δD, and deuterium excess (d_x) records of ice wedges, with δ¹⁸O values ranging from -29 to -20% (SMOW) and d_x values ranging from -6 to +9% (SMOW). Paleotemperatures during ice wedge formation were determined using the equation T(°C) = δ¹⁸O/0.80 derived from Alaskan stations within the Global Network of Isotopes in Precipitation (GNIP) database. Assuming no change in moisture source over time, the middle stratigraphic unit ice wedges formed when temperatures were the coldest, with the lower stratigraphic unit ice wedges forming when temperatures were 3 <u>+</u> 0.3°C higher, and the upper stratigraphic unit wedges forming when temperatures were 9 <u>+</u> 0.3°C higher. In wedge 58N, δ¹⁸O values of -24% at the outer edge of the wedge and δ¹⁸O values of -27% in the center of the wedge indicate formation began in warmer conditions, growth occurred during a cold period, and growth terminated abruptly during the onset of a warming event. Dissolved organic carbon (DOC) dates of 26,879 <u>+</u> 579 cal yr BP indicate the lower unit wedges began forming during Heinrich Event 2 (H2). Isotopic signatures of small wedges in the uppermost unit in the tunnel indicate formation occurred during later cold events in Central Alaska. These stable isotope data provide insight into the possible response of Central Alaska to North Atlantic Heinrich event forced climatic variability during the Late Pleistocene.