Sedimentary metal ratios in the Colombia Basin as indicators for water balance change in northern South America during the past 400,000 years
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2005-11-15
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AMER GEOPHYSICAL UNION
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Recent paleoclimate reconstructions for northern South America suggest changes in moisture balance interpreted to result from shifts in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). Because most of these records only extend back to the last glacial interval, we measured metal abundances in sediments from Ocean Drilling Program Core 999A in the Caribbean Sea spanning the last 400 kyr to evaluate glacial/interglacial fluctuations in the water balance of northern South America. Variations in sedimentary Al/Ti, K/Ti, Fe/Ti, and Fe/Al ratios are interpreted to reflect changes in riverine input through the Magdalena River. The measured metal ratios show a strong 100-kyr cyclicity, which could reflect changes in sedimentation related to sea level fluctuations or to climate. Although the variability in Fe/ Ti and Fe/Al ratios points to rainfall-induced changes in the mineralogy of the terrigenous fraction, shelf erosion induced by sea level fluctuations cannot completely be ruled out. If climate accounted for changes in the nature of the terrigenous components, then the strong 100-kyr fluctuations in the measured metal ratios would point to the influence of high-latitude climate on the local hydrological balance of northern South America with ice volume growth forcing a southward displacement of the ITCZ. Copyright 2005 by the American Geophysical Union.