Patterns and causes of millennial-scale climate change in the Pacific Northwest during Marine Isotope Stages 2 and 3

Abstract

A high-resolution pollen record from Fargher Lake, Washington shows a series of millennial-scale changes in vegetation and climate during marine isotope stages (MIS) 3 and 2. A comparison of Fargher Lake with pollen records from Little Lake, Oregon and Carp Lake, Washington, reveals regional patterns of change. During the early part of MIS 3 (ca 60,000–45,000 cal yr BP), Fargher and Carp lakes indicate transitions between open and closed vegetation and cold dry and warm wet conditions. Between 45,000 and 27,500 cal yr BP, all three records show shifts between low- and high-elevation taxa that indicate a series of temperature changes. These temperature changes are similar to those in the Santa Barbara Basin and may be explained by changes in the strength of the Aleutian low. During MIS 2 (27,500–14,000 cal yr BP), shifts between wet- and dry-adapted taxa were most prominent at Little Lake. There is also evidence for two minor warmings. MIS 2 climate variations do not correlate well with those in the Santa Barbara Basin. However, precipitation changes in the Pacific Northwest during MIS 2 correlate with evidence of ice-sheet surges into the North Atlantic and were probably related to variations in the strength and position of the glacial anticyclone and the jet stream.