Late Glacial to Early Holocene Climate Oscillations in the American Southwest Kenneth Cole, USGS Southwest Biological Science Center Flagstaff, AZ;
[email protected] View of the Grand Canyon North Rim (2500 m) from a mid elevation (1500 m) on the South Rim. 1 Most of the earliest conceptions of the Pleistocene versus Holocene plant zonation consisted of lower Pleistocene zones and higher Holocene zones without much information on how they shifted from one to the other. 2 15,000 year-old packrat midden in a Grand Canyon cave. Steven’s Woodrat (Neotoma stevensii) poses with Kirsten Ironside. 3 Lower Colorado River Elevational Zonation Treeline Snowline 3000 Spruce Forest Treeline Modified From: Ponderosa Pine - Fir Forest Cole, K. L. 1990. Reconstruction Spruce Forest of past desert vegetation along the Colorado River using packrat 2000 middens. Palaeogeography, Palaeoclimatology, and Pinyon-Juniper Woodland Limber Pine, Fir Forest Palaeoecology 76: 349-366. Blackbrush - Sagebrush Juniper - Sagebrush Elevation (m) Desert Woodland 1000 Juniper - Ash Juniper - Blackbrush Brittle Bush - Woodland Woodland Creosote Bush Desert Joshua Tree - Brittle Bush - Creosote Bush Desert Sea Level Brittle Bush - Creosote Bush - Catclaw 0 5000 10000 15000 20000 Radiocarbon age (yr B.P.) K. Cole, 1995 This diagram shows a species individualistic approach made possible from plant macrofossils in packrat middens. There was still little information on the rapid Pleistocene to Holocene shift although intermediate plant assemblages were identified. 4 Carbon 13 values of packrat pellets from 92 fossil middens from the Grand Canyon, AZ Adapted From: Cole, K. L. and S. T. Arundel, 2005. Carbon 13 isotopes from fossil packrat pellets and elevational movements of Utah Agave reveal Younger Dryas cold period in Grand Canyon, Arizona.