HR: 1330h
AN: PP32B-0300    [PDF]
TI: Historic Carbon Isotopic Shifts in Pinyon Pines and Woodland Junipers are Unprecedented During the Quaternary History of These Taxa
AU: * Van de Water, P K
EM: pvandewater@usgs.gov
AF: U.S. Geological Survey, c/o U.S. EPA 200 SW 35th St., Corvallis, OR 97333 United States
AU: Leavitt, S W
EM: sleavitt@ltrr.arizona.edu
AF: Laboratory of Tree-ring Research, University of Arizona, Tucson, AZ 85721 United States
AU: Betancourt, J L
EM: jlbetanc@usgs.gov
AF: U.S. Geological Survey, Desert Laboratory 1675 W. Anklam Road, Tucson, AZ 85745 United States
AB: Packrat ({\it Neotoma}) midden macrofossil records from arid and semiarid western North America provide evidence that pinyon pines and woodland junipers have grown together for at least the past 50,000 radiocarbon years. The midden records show that this association was sustained despite large-scale changes in climate and atmospheric CO$_{2}$ concentrations over the past 50 millenia. Reconstruction of physiological parameters, using $^{13}$C analysis of a select sample of pinyon pine and juniper macrofossils from radiocarbon-dated ancient packrat middens, shows distinct physical responses to these changes despite a offset between the carbon isotopic values of the two genera, with pinyon pines having consistently lower $^{13}$C values than junipers. Remarkably, analysis of historic (from herbarium sheets) and present-day (from field collections) materials from northern Arizona and the Four-Corners region indicates that the long-term offset between the carbon isotopic values of pinyon pines and woodland junipers has inverted; with the junipers now providing isotopically lighter values than the pinyon pines. This reversal began in the late 1800's to early 1900's and has widened over the past century. The inverted isotopic offsets in the historic period may be due to the unprecedented levels of carbon dioxide and other trace gases in the atmosphere.
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting