Late Glacial to Early Holocene Climate Oscillations
in the American Southwest
Kenneth Cole, USGS Southwest Biological Science Center
Flagstaff, AZ; ken_cole@usgs.gov
View of the Grand Canyon North Rim (2500 m) from a mid elevation (1500 m) on the South Rim.
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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.
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Lower Colorado River Elevational Zonation
Treeline
Snowline
3000
Spruce Forest
Treeline
Modified From:
Spruce Forest
2000
Elevation (m)
Cole, K. L. 1990. Reconstruction
of past desert vegetation along the
Colorado River using packrat
middens. Palaeogeography,
Palaeoclimatology, and
Palaeoecology 76: 349-366.
Ponderosa Pine Fir Forest
Pinyon-Juniper
Woodland
Limber Pine, Fir Forest
Blackbrush Sagebrush
Desert
Juniper - Sagebrush
Woodland
1000
Brittle Bush Creosote Bush
Desert
Juniper - Ash
Woodland
Juniper - Blackbrush
Woodland
Joshua Tree - Brittle Bush Creosote Bush Desert
Sea Level
Brittle Bush - Creosote Bush - Catclaw
0
5000
10000
15000
Radiocarbon age (yr B.P.)
20000
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. Geology 33: 713-716.
More recent data is coming from archives of previously collected midden assemblages that can now be used in the
application of new techniques providing that there has been adequate funding for storage and curation of older
collections (an unusual occurrence).
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Holocene
YD B/A
Holocene YD
B/A
Adapted From: Cole and Arundel, 2005, Geology 33: 713-716.
This diagram shows the late Pleistocene climate oscillations from the warm Bolling/Allerod to the cold Younger Dryas,
followed by the rapid temperature increase as the Holocene started. These changes are shown in the shifts of carbon
isotopes and well as the upper elevational limit of Utah Agave. This limit (blue line) is controlled by winter minimum
temperature which was 8 degrees colder than today during the Younger Dryas. These rapid shifts were invisible until
new AMS Radiocarbon analyses made possible better dating control.
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Eastern Grand Canyon
Potato Lake
7
Heinrich Event 0
= Younger Dryas
Allerod?
Plant macrofossil analysis from Potato Lake also suggests a warm Allerod Period.
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ODP Core 1019
Data from ocean cores are in agrement with the terrestrial data and far more detailed.
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Adapted From:
Barron, J.A., Huesser, L., Herbert, T., and Lyle, M., 2003, High-resolution climatic evolution of
coastal northern California during the past 16,000 years: Paleoceanography, v. 18, p. 1020–1035.
Grootes, P.M., and Stuiver, M., 1997, Oxygen 18/16 variability in Greenland snow and ice with 103to 105-year time resolution: Journal of Geophysical Research, v. 102, p. 26,455–26,470.
This ocean core (top) suggests a 4 degree (C) cooling of mean annual temperature in the Younger Dryas. If winter
temperatures were 8 degrees colder, yet annual only 4 degrees, then summer temperatures were only a degree or two
colder as shown in some pollen studies.
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Full Glacial
Bolling/ Younger Early
Allerod Dryas Holocene
The disparity in summer versus winter solar insolation caused this difference between summer and winter temperatures
in the Younger Dryas.
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Carbon 13 in
Grand Canyon
Packrat Pellets
Concentration of
fossil Agave in
Grand Canyon
Packrat Middens
ODP1019
Barron et al. 2003
GISP2
Stuiver et al. 1997
Alkenone derived
mean annual sea
surface temperature
from CA / OR border.
Oxygen 18 from
Greenland Ice Core
All of these data show a rapid warming of at least 4 degrees C around 11,600 years ago at the end of the Younger
Dryas. This is similar in rate and magnitude to the change expected to starting now due to global warming.
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YD
Modified from:
Cole, K., 1985, Past rates of change,
species richness, and a model of
Vegetational Inertia in the Grand
Canyon, Arizona. American
Naturalist 125:289-303.
The previous shifts in climate caused lower species diversity of trees and shrubs as shown in these older poorly dated
middens. Current analyses are underway to improve these data.
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Global Warming and the rapid invasions of weedy species are related to the relatively slow response of trees and shrubs
to warming as seen at the end of the Younger Dryas.
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The end.
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