Evidence for millennial-scale climate change during marine isotope stages 2 and 3 at Little Lake, western Oregon, USA

Pollen and geochemical data from Little Lake, western Oregon, suggest sever al patterns of millennial-scale environmental change during marine isotope stage (MIS)2 (14,100-27,600 cal yr B.P.) and the latter part of MIS 3 (27,6 00-42,500 cal yr B.P.). During MIS 3, a series of transitions between warm- and cold-adapted taxa indicate that temperatures oscillated by ca, 2 degre es -4 degreesC every 1000-3000 yr. Highs and lows in summer insolation duri ng MIS 3 are generally associated with the warmest and coldest intervals. W arm periods at Little Lake correlate with warm sea-surface temperatures in the Santa Barbara Basin. Changes in the strength of the subtropical high an d the jet stream may account for synchronous changes at the two sites. Duri ng MIS 2, shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000-3000 yr. Increases in Tsuga heterophylla pollen at 25,000 and 22,000 cal yr B.P. imply brief warmings, Minimum summer inso lation and maximum global ice-volumes during MIS 2 correspond to cold and d ry conditions. Fluctuations in precipitation at Little Lake do not correlat e with changes in the Santa Barbara Basin and may be explained by variation s in the strength of the glacial anticyclone and the position of the jet st ream. (C) 2001 University of Washington.