HOLOCENE MILLENNIAL-SCALE CLIMATE VARIABILITY IN WESTERN NORTH AMERICA

We compare several high-resolution paleoclimatic records from western North America that indicate near-synchronous millennial-scale climate variability through much of the Holocene. A Holocene pluvial lake system in northern Chihuahua, Mexico alternates between lake highstands representing cooler and wetter conditions and dry playa conditions representing warmer, drier climates. Alpine lakes and bogs from the Sangre de Cristo Mountains of northern New Mexico record a series of glacial and periglacial events (colder, effectively wetter climates) that alternate with warmer, drier climates over the late Pleistocene and the Holocene. Forest fire-related sedimentation and alluvial activity from northeast Yellowstone National Park also shows a clear response to millennial-scale climate change during the Holocene. Pulses of fire-related debris flow activity occur during warmer, drier periods that are more prone to droughts. These alternate with cooler, effectively wetter conditions that produce more river discharge and form broad flood plains later preserved as terraces.

Pluvial lake highstands in northern Mexico are centered at the following calendar ages: 230 ka, 4,250 ka, 7,400 ka, and 9,300 ka. The northern New Mexico chronology shows cold, effectively wetter climates at the following calendar age midpoints: 200 ka, 3,000 ka, 3,900 ka and 5,700 ka. The Yellowstone chronology shows cold, effectively wetter climates during the following age ranges: 300 to 600 ka, 1,400 to 1,600 ka, 2,800 to 3,100 ka, 3,900 to 4,300 ka, and 5,500 to 6,000 ka. In the Rocky Mountain records, the millennial-scale events are more prominent during the late Holocene Neoglacial interval than during the early to middle Holocene. These climate events in western North America reflect widespread temperature anomalies and to a lesser extent, precipitation anomalies. The cold phases of these events correlate with a North Atlantic record of ice-rafting and cool events (Bond et al., 2001) and suggest that millennial-scale climate changes are at least hemispheric in extent during much of the Holocene.