Orbital forcing signal in sediments of two Amazonianlakes |
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| Authors: | MB Bush MC Miller PE De Oliveira PA Colinvaux |
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| Institution: | (1) Department of Biological Sciences, Florida Institute of Technology, 32901 Melbourne, USA;(2) Department of Biological Sciences, University of Cincinnati, 54221 Cincinnati, USA;(3) Department of Botany, The Field Museum of Natural History, 60605 Chicago, USA;(4) Marine Biological Laboratory, 02543 Woods Hole, USA |
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| Abstract: | Paleolimnological data from two ancient lakes at 0° latitudein Amazonia indicate that past lake level changes reflect precessional (19,000to 22,000 years) variations in insolation over the last 170,000 years. Waterlevel in Lakes Pata and Verde, Brazil, is determined by the ratio ofprecipitation:leakage. Times of low lake level are indicated in sediments byoxidized clays, evidence of algal blooms and high K+ concentrations.Peak K+ values are attributed to biogenic concentration when thelake was reduced to a shallow, productive pool. Low lake phases correlate withmaximum insolation during the dry season (June–July–August). Thusthe last glacial maximum 18,000 to 22,000 yr BP was a wet time in northernAmazonia, and the driest period of the last 170,000 years was from 35,000 to27,000 yr BP. These results from near the equator do not imply thatprecipitation changed synchronously across Amazonia, because geographiclocations throughout the vast watershed were undoubtedly influenced by localmoisture sources. |
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| Keywords: | Amazon Cation Ice age ITCZ Lake level Milankovitch Orbital forcing Precipitation |
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