HR: 15:30h
AN: GC53A-12    [Abstracts]
TI: A comparison of speleothem and lake sediment core \delta$^{18}$O records from the north-central Yucatan Peninsula, Mexico
AU: * Hodell, D A
EM: dhodell@geology.ufl.edu
AF: University of Florida, Department of Geological Sciences, PO Box 12120, Gainesville, FL 32611 United States
AU: Brenner, M
EM: brenner@ufl.edu
AF: University of Florida, Department of Geological Sciences, PO Box 12120, Gainesville, FL 32611 United States
AU: Curtis, J H
EM: curtisj@ufl.edu
AF: University of Florida, Department of Geological Sciences, PO Box 12120, Gainesville, FL 32611 United States
AU: Gallup, C C
EM: cgallup@d.umn.edu
AF: University of Minnesota Duluth, Dept. of Geological Sciences 229 Heller Hall 1114 Kirby Drive , Duluth, MN 55812
AB: Paleoclimate studies in the Maya lowlands of Mesoamerica using lake sediment cores revealed relationships between times of drought and Maya cultural change. Here we test lake-based climatic inferences using oxygen isotopes of calcite from a stalagmite collected in a cave near Hobonil, Mexico, on the northern-central Yucatan Peninsula. The 30-cm stalagmite (Hobo-2) yielded a basal U/Th age of 1746\pm123 years ($\sim$250 AD.). This suggests that it grew throughout the Early and Late Classic Periods (250 - 800 AD.) when the Maya reached their cultural apex, and during the terminal Classic Period ($\sim$800-1000 AD.) when the civilization declined. Samples were drilled every 0.5 mm along the speleothem growth axis, yielding a mean temporal sampling resolution of 2.5 years, assuming a constant growth rate of $\sim$0.2 mm per year. The mean \delta$^{18}$O value over the stalagmite's length is -3.3\permil with a range of $\sim$2\permil (from -2.3 to -4.3\permil). Oxygen isotope variation in Hobo-2 is interpreted to reflect the \delta$^{18}$O of weighted mean annual precipitation, which is correlated with rainfall amount in the region. Evaporation effects on \delta$^{18}$O are also possible because the stalagmite was collected relatively near the cave entrance. We define dry conditions as periods when \delta$^{18}$O values exceed 1-standard deviation of the mean. The longest duration of dry climate for the last 1750 yrs occurred during the Terminal Classic period between ~800 and 1000 AD, confirming previous paleolimnological evidence for a protracted drought at that time. Dry events of shorter duration are centered at $\sim$620, 1410, and 1620 AD. The speleothem chronology is preliminary and based on the assumption of constant growth rate. Nonetheless, the oxygen isotope record of Hobo-2 is very similar to the \delta$^{18}$O records from shell carbonate in nearby Lakes Chichancanab and Punta Laguna, providing independent evidence of the climate history of the north-central part of the Yucatan Peninsula. Additional U/Th dates on speleothems will provide more accurate ages for climate events than has been possible with radiocarbon dating of lake sediment cores. Even AMS $^{14}$C dates on definitively terrestrial organic matter have calibrated age errors of +/-100 years. Because the karsted Yucatan Peninsula has abundant caves, speleothems hold much promise for reconstructing past climate and assessing its role in Maya cultural transformation.
DE: 3344 Paleoclimatology
DE: 1040 Isotopic composition/chemistry
SC: Global Climate Change [GC]
MN: 2004 AGU Fall Meeting