HR: 08:45h
AN: PP11C-04    [Abstracts]
TI: Glaciation and Hydrologic Variability in Tropical South America During the Last 400,000 Years
AU: * Fritz, S C
EM: sfritz2@unl.edu
AF: University of Nebraska, Department of Geosciences, Lincoln, NE 68588-0340 United States
AU: Baker, P A
EM: pbaker@duke.edu
AF: Duke University, Division of Earth and Ocean Sciences, Durham, NC 27708 United States
AU: Seltzer, G O
EM: goseltze@syr.edu
AF: Syracuse University, Department of Earth Sciences, Syracuse, NY 13244 United States
AU: Ekdahl, E J
EM: eekdahl2@unlnotes.unl.edu
AF: University of Nebraska, Department of Geosciences, Lincoln, NE 68588-0340 United States
AU: Ballantyne, A
EM: apb14@duke.edu
AF: Duke University, Division of Earth and Ocean Sciences, Durham, NC 27708 United States
AB: The expansion and contraction of northern continental ice sheets is a fundamental characteristic of the Quaternary. However, the extent of tropical glaciation is poorly constrained, particularly for periods prior to the Last Glacial Maximum (LGM). Similarly, the magnitude and timing of hydrologic variation in tropical South America is not clearly defined over multiple glacial cycles. Thus, the relative roles of global temperature change and insolation control of the South American Summer Monsoon (SASM) are unclear. We have reconstructed the timing of glaciation and precipitation variability in the tropical Andes of South America from drill cores from Lake Titicaca, Bolivia/Peru. The longest core (site LT01-2B, 235 m water depth) is 136 m and consists of four major silt-dominated units with high magnetic susceptibility, low organic carbon concentration, and no carbonate, which are indicative of extensive glacial activity in the cordillera surrounding the lake. These units alternate with laminated low-susceptibility units, with high carbonate and organic carbon concentrations, which reflect times when detrital input from the watershed was low and lake-level was lowered to below the outlet threshold, driving carbonate precipitation. Thus, the stratigraphy suggests that the core spans four major periods of glaciation and the subsequent interstadials. Core chronology is based on radiocarbon in the uppermost 25m, U-series dates on aragonite laminae, and tuning of the calcium carbonate stratigraphy in the lowermost sediments to the Vostok CO2 record. High-resolution (ca. 100 yr) sampling of sediments spanning the last glacial stage shows distinct millennial-scale variability from 20 - 65 kyr BP. This variability is evident in the periodic deposition of turbidites, which are characterized by low biogenic silica concentrations, elevated benthic diatom abundances, heavy carbon isotopic values, high C/N ratios, and an increase in mean grain size - a composite signal indicative of enhanced input to this deepwater site of material originally deposited in nearshore regions of the lake. U-series ages at the top of the penultimate (pre-Holocene) unit of laminated sediments suggest that the last major low stand of Lake Titicaca dates from MIS 5.5. Diatom data indicate that this was the most saline interval in the recovered sequence and thus suggest that MIS5.5 was the time of maximum aridity. The tuned drill-core magnetic susceptibility record suggests that glacial stages in the tropical Andes were approximately synchronous with high-latitude glacial stages and globally cold climate, with increased glacial activity in the periods 370-322, 300-238, 230-213, 188-139, and 65-15 kyr BP. Overall, the intervals of increased glaciation are periods when Lake Titicaca was deep, fresh, and overflowing, as inferred from calcium carbonate concentration, carbon isotopic values, and the diatom composition. The timing of lake-level change relative to high-latitude climate and insolation variation suggests that the water balance of the tropical Andes was at least as strongly influenced by global temperature change and global-scale boundary conditions as by insolation control of the SASM.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
DE: 4926 Glacial
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005