HR: 1340h
AN: U13B-1157    [Abstracts]
TI: A Speleothem Record of Tropical Moisture Transport
AU: * Johnson, L R
EM: lrj80@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, MSC03-2040 1 University of New Mexico, Albuquerque, NM 87131, United States
AU: Asmerom, Y
EM: asmerom@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, MSC03-2040 1 University of New Mexico, Albuquerque, NM 87131, United States
AU: Lachniet, M S
EM: Matthew.Lachniet@unlv.edu
AF: University of Nevada Las Vegas, Department of Geoscience, 4505 Maryland Pkwy, Las Vegas, NV 89154, United States
AU: Burns, S J
EM: sburns@geo.umass.edu
AF: University of Massachusetts Amherst, Department of Geosciences, 611 North Pleasant St 233 Morrill Science Center, Amherst, MA 01003, United States
AU: Patterson, W P
EM: Bill.Patterson@usask.ca
AF: University of Saskatchewan, Department of Geological Sciences, 114 Science Place, Saskatoon, SK S7N 5E2, Canada
AB: It has been suggested that the tropics may modulate changes in climate normally associated with high latitude forcing. One suggested mechanism is moisture transport from the Atlantic to the Pacific across Central America. We present a long-term, high- resolution speleothem record from western Costa Rica that documents change in local precipitation in the tropics during the Late Pleistocene (96.9 to 44.4 ka) and has important implications for moisture transport. Oxygen isotope signatures preserved in tropical speleothem calcite, precisely dated using uranium-series, provide a direct record of local moisture variability. The δ¹⁸O values in our speleothem range from -10.0‰ to -5.2‰ VPDB. The δ¹⁸O values and amount of precipitation are inversely correlated in the tropics due to the amount effect. Essentially, progressive rainout of a given air mass drives the δ¹⁸O value of the water to increasingly negative values due to localized convection. High precipitation intervals at the study site are due to either 1) an increase in Atlantic-sourced moisture transported across the isthmus, or 2) increased evaporation and convection of local Pacific waters. Progressive rainout from the Atlantic to the Pacific is documented in modern surface waters and speleothems, so excursions toward lower δ¹⁸O values may correspond to enhanced moisture transport from the Atlantic. Paleosalinity data are consistent with this inference. However, the stable isotope data from this study also correspond with sea surface temperature (SST) anomalies in the tropical Atlantic, as well as changes in the SST gradient of the two ocean basins. These temperature patterns and the corresponding precipitation record from the study area are analogous to the modern response to ENSO. Although our paleoprecipitation data do not distinguish between the above two scenarios as of yet, with additional analysis they may provide important constraints for models that invoke tropical moisture transport as a climate modulator.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1620 Climate dynamics (0429, 3309)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Union [U]
MN: 2007 Fall Meeting