Mora, German; Hinnov, Linda (2005): Orbital forcing of tropical water balance inferred from sulfur speciation in lake sediments. Geological Society of America (GSA), Boulder, CO, United States, In: Mora, German (editor), Surge, Donna (editor), Isotopic and elemental tracers of Cenozoic climate change, 395, 33-42, georefid:2006-011047

Although water balance in terrestrial settings is an important climate parameter, relatively few proxies are available for reconstructing effective moisture. Here, we investigate the possibility of using sulfur speciation as a proxy for paleorainfall in sediments recovered from a large paleolake in the Bogota Basin, Colombia and spanning the past 660 k.y. Samples were digested with a mild acidic solution to extract acid-soluble sulfur minerals. Sulfur species extracted through this procedure included monosulfides, whereas sulfur in the remaining acid-insoluble fraction was found to be bound to organosulfur compounds. Monosulfide/total sulfur ratios range from 0.2 to 0.9 in the studied sediments and exhibit a cyclic distribution with depth. Low (<0.4) monosulfide/total sulfur ratios are characteristic of glacial intervals, whereas interglacial intervals exhibit both low and high ratios. Because partitioning of sulfur between monosulfides and organosulfur compounds depends on iron availability, we interpret that elevated iron delivery to the paleolake occurs at relatively high precipitation rates and results in the sequestration of sulfur in monosulfide minerals. Conversely, incorporation of sulfur into organic matter occurs at low precipitation rates when iron supply is low. Time-series analysis of sulfur ratios reveals the influence of orbital parameters (i.e., eccentricity, obliquity, and precession). Given that rainfall in the tropics is primarily associated with the passage of the Intertropical Convergence Zone, we conclude that orbital forcing exerts a significant control on the intensity or zonality of the Intertropical Convergence Zone that ultimately affects rainfall patterns in the Colombian Andes.
West: -83.4414 East: -74.0500 North: 4.3800 South: 1.1203
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