HR: 10:50h
AN: PP21D-03    [PDF]
TI: 500,000-year History of Fluvial Discharge into the Caribbean Sea as Revealed by Elemental Geochemical Analysis of ODP Site 999A
AU: * Mora, G
EM: gmora@iastate.edu
AF: Department of Geological and Atmospheric Sciences Iowa State University, 253 Science I, Ames, IA 50011-3212 United States
AU: Martinez, I
EM: jimartin@eafit.edu.co
AF: Departamento de Geologia Universidad EAFIT, A.A. 3300, Medellin, 50011 Colombia
AB: Records spanning the last glacial/interglacial interval indicate significant changes in the moisture balance of the neotropics. Because the Intertropical Convergence Zone (ITCZ) plays a critical role in controlling the hydrological balance of the tropics, past changes in rainfall patterns have been interpreted as resulting from long-term fluctuations in the zonality and/or intensity of the ITCZ. To evaluate glacial/interglacial changes in the ITCZ beyond the last glaciation, we are studying a marine core from the Caribbean Sea. Our goal is to reconstruct changes in the hydrological balance of northern South America, which are chiefly driven by fluctuations in the ITCZ. For this purpose, we study the upper 20 m of ODP Site 999A from the Colombia Basin. The chronology of the record is based on the oxygen-isotopic composition of specimens of planktonic foraminefera (G. sacculifer and Neogloboquadrina dutertrei) that were manually picked out of sediment samples. The obtained isotopic record indicates that the studied interval encompasses the last ~500,000 years, which is also supported by chronostratigraphic control provided by the relative abundance of Globorotalia menardii, G. inflata, and G. truncatulinoides. Detrital material accumulating in the Colombia Basin mainly comes from the Colombian Andes via the Magdalena River. Because measurements of detrital load in the river show a strong relationship with rainfall in the northern Andes, we use titanium and aluminum concentrations in the sediment samples as proxies for detrital material influx from the northern Andes. Our results show that while high aluminum/titanium ratios occur in interglacial intervals, low ratios typically occur in glacial intervals. Time-series analysis indicates a cyclic distribution of titanium and aluminum concentrations, showing periodicities closely related to Earth's orbital variations. We interpret these cyclic distributions of titanium and aluminum as evidence for glacial/interglacial fluctuations in the dynamics of the ITCZ that were forced by orbital-induced changes in insolation.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 3022 Marine sediments--processes and transport
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting