Millennial-scale vegetation and climate variations in the Pacific Northwest during the last glacial period (60,000--16,000 cal yr B.P.)

Pollen, lithologic, and geochemical records from three sites in the Pacific Northwest document millennial-scale paleoenvironmental variations during marine isotope stages (MIS) 3 and 2. Fargher and Little lakes are low-elevation lakes in western Oregon and Washington and Carp Lake is a mid-elevation lake in central Washington. During the early part of MIS 3 (ca. 60,000--45,000 cal yr B.P.), Fargher and Carp lakes show a series of changes in vegetation that reflect shifts in climate, occurring every 1000--3000 years. Periods of open vegetation indicate cold and/or dry conditions, while those of closed vegetation suggest warm and/or wet conditions. Between 45,000 and 27,500 cal. yr B.P., transitions between low- and high-elevation forest taxa at all three sites imply a series of temperature oscillations also occurring every 1000--3000 years. Variations in organic carbon percentages at Fargher and Little lakes indicate increased lake productivity during warm periods. During MIS 2 (27,500--14,000 cal yr B.P.), the Little Lake record shows shifts between wet- and dry-adapted subalpine taxa at a similar frequency as climate variations during MIS 3. Small changes in the abundance of wet-adapted subalpine taxa at Fargher and Carp lakes indicate similar changes in precipitation. Fargher and Little lakes also contain evidence of two warm periods.; Temperature fluctuations in the Pacific Northwest during MIS 3 are similar in frequency and often in timing to those evident in records from the Santa Barbara Basin and Greenland. Concurrent fluctuations in the Pacific Northwest and Santa Barbara Basin may be explained by changes in the strength of the Aleutian low and/or the East Pacific subtropical high. During MIS 2, fluctuations in precipitation and less frequent changes in temperature in the Pacific Northwest do not correlate well with those in other regions. However, precipitation changes correlate with evidence for ice sheet surges into the North Atlantic. Fluctuations in precipitation during MIS 2 were probably related to variations in the strength of the glacial anticyclone and the position of the jet stream, which resulted from changes in the height of the Laurentide Ice Sheet.; This dissertation includes material that is in review for publication and has been co-authored.