A biogenic-silica δ18O record of climatic change during the last glacial-interglacial transition in southwestern Alaska

Despite growing evidence for environmental oscillations during the last glacial-interglacial transition from high latitude, terrestrial sites of the North Pacific rim, oxygen-isotopic records of these oscillations remain sparse. The lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen-isotopic analysis. We report here the first record of oxygen-isotopic composition in diatom silica (delta(18)O(Si)) from a lake in that region. delta(18)O(Si) increases gradually from 19.0 to 23.5parts per thousand between 12,340 and 11,000 C-14 yr B.P., reflecting marked climatic warming at the end of the last glaciation. Around 11,000 C-14 yr B.P., delta(18)O(Si) decreases by 1.7parts per thousand, suggesting a temperature decrease of 3.5-8.9 degreesC at the onset of the Younger Dryas (YD) in southwestern Alaska. Climatic recovery began ca. 10,740 C-14 yr B.P., as inferred from the increase of delta(18)O(Si) to a maximum of 23.9parts per thousand near the end of the YD. Our data reveal that a YD climatic reversal in southwestern coastal areas of Alaska occurred, but the YD climate did not return to full-glacial conditions. (C) 2003 Elsevier Science (USA). All rights reserved.