HR: 0800h
AN: PP51F-1378    [Abstracts]
TI: The Terrestrial Paleoclimatic Record of the Late Quaternary as Revealed by Drilling Lake Titicaca, Peru/Bolivia
AU: * Baker, P A
EM: pbaker@duke.edu
AF: Duke University, Division of Earth and Ocean Sciences Box 90227, Durham, NC 27708-0227 United States
AU: Fritz, S C
EM: sfritz2@unl.edu
AF: University of Nebraska, Department of Geosciences, Lincoln, NE 68588 United States
AU: Seltzer, G O
EM: goseltze@mailbox.syr.edu
AF: Syracuse University, Department of Earth Sciences, Syracuse, NY 13244 United States
AU: Ballantyne, A P
EM: apb14@duke.edu
AF: Duke University, Division of Earth and Ocean Sciences Box 90227, Durham, NC 27708-0227 United States
AU: Rigsby, C A
EM: rigsbyc@mail.ecu.edu
AF: East Carolina University, Department of Geology, Greenville, NC 27858 United States
AB: Seven drill cores were recovered from Lake Titicaca during the NSF/ICDP/DOSECC drilling expedition of 2001; our most detailed multi-proxy analyses have been done on Core 2B raised from 232 m water depth in the central basin of the lake. This site was drilled to 139 mblf with 141 m of total sediment recovered (101%). The recovered sediments consist of two main lithologies, organic- and inorganic-carbon-rich (often-laminated) muds that alternate with detrital-rich muds. These lithologies represent respectively low and high lakestand deposits. Proxies for water level include planktic-to-benthic diatom ratio, sedimentary carbonate content, and stable isotopic ratio of organic carbon. There are six highstand intervals separated by five lowstand intervals indicating that the level and volume of Lake Titicaca underwent several large changes during the late Quaternary. We infer from high values of magnetic susceptibility in most highstand muds that glacial advances in the surrounding Andes coincided with periods of relative wetness. During the most recent lowstand, in the early and middle Holocene, Lake Titicaca fell to 85 m below its modern level, salinity increased several-fold, and the downstream Salar de Uyuni desiccated. By contrast, throughout the LGM from ca. 25,000 cal BP to 15,000 cal BP, Lake Titicaca was deep and fresh, and overflowed southward to the Salar de Uyuni. Prior to the LGM, back to ca. 53,000 BP, the lake was predominantly fresh and overflowing. Pulses of increased benthic diatom abundance and inorganic carbon concentration during that time were likely due to episodes of downslope transport. We believe (based on U-Th dates of authigenic carbonate layers) that the penultimate lowstand of Lake Titicaca (seismic evidence indicates a lake level 200 m lower than today) was coincident with MIS 5. We recovered sediments recording three older lowstands, each separated by periods in which the lake freshened dramatically and when glaciers apparently advanced in the Andes. We tentatively correlate these lowstands with MIS 7, 9, and 11. The high abundance of benthic diatoms in the lowermost 40 m of drill core may imply that the Altiplano was persistently drier than today, prior to and including MIS 9. Alternatively, basin morphometry may have been significantly different than today because of geomorphic or tectonic effects. This period apparently coincides with a period when the Salar de Uyuni was mostly dry and dominated by salt deposition.
DE: 9360 South America
DE: 9604 Cenozoic
DE: 3344 Paleoclimatology
DE: 1845 Limnology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting