HR: 09:15h
AN: PP11C-06 INVITED     [Abstracts]
TI: Millennial Scale Variability in Tropical South American Vegetation During the Last Glaciation
AU: * Hughen, K
EM: khughen@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Drenzek, N
EM: ndrenzek@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Eglinton, T
EM: teglinton@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AU: Bice, M
EM: mbice@whoi.edu
AF: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd., Woods Hole, MA 02543 United States
AB: Millennial scale climate variability mirroring the Dansgaard-Oeschger events in Greenland ice cores has been recorded at locations around the globe. The forcing mechanisms responsible for these abrupt changes are hypothesized to originate at either high or low latitudes, but no evidence has yet confirmed either location. Detailed records of past shifts in the tropical hydrological cycle are needed to evaluate its potential role in causing abrupt global climate changes. The Cariaco Basin, off northern Venezuela, is situated along the northern margin of the seasonal range of the InterTropical Convergence Zone. Previously, vascular plant biomarkers have shown abrupt changes in terrestrial vegetation over northern South America, concurrent with rapid climate shifts of the last deglaciation. Carbon isotopes from long-chain n-alkanoic acids, a proxy for C3 versus C4 metabolic pathways, indicate that C3 plants predominated in the Cariaco watershed during warm/wet Bolling-Allerod and Holocene periods, and C4 plant biomass proliferated during cool/dry late Glacial and Younger Dryas intervals. The leaf wax data reveal that local vegetation biomass, although not necessarily entire biomes, shifted between arid grassland and wetter forest taxa on timescales of decades. Here we present new data from sediments of ODP Site 1002D in the Cariaco Basin that provide a record of terrestrial vegetation change and ITCZ variability over the past 60,000 years. Compound-specific carbon isotopes were measured on leaf waxes at about 500 year intervals, resolving millennial scale changes during Marine Isotope Stage 3. The complete record shows distinct isotopic shifts concurrent with D-O and Heinrich events in the high latitude N. Atlantic region. During D-O stadials and particularly Heinrich events, isotope ratios shift to enriched values, indicating increased C4 plant biomass and more arid conditions. The largest anomalies are seen during Heinrich events H0-H6, with isotopic shifts of up to 8 per mil. In addition, a strong orbital signal is present at the precessional time scale. Insolation during November at the end of the Cariaco rainy season appears to modulate the amplitude of ITCZ shift during D-O and Heinrich events. This may indicate that the ITCZ is responding to, rather than driving, rapid millennial scale climate changes during the last Glacial period.
DE: 1055 Organic and biogenic geochemistry
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005