Pleistocene Precipitation Balance in the Amazon Basin Recorded in Deep Sea Sediments

m a r Terrigenous sediments from Ceara Rise in the western ropical Atlantic Ocean record Pleistocene Amazon Basin cliate variability. Iron oxides and oxyhydroxides in this region riginate mainly from chemically leached Amazon lowland oils. Concentrations of goethite and hematite in the terrignous fraction consistently peak during transitions from lacial to interglacial periods, suggesting an increased proporion of erosive products derived from the Amazon lowlands ompared to the physically weathered highlands. Lowland Amzon Basin precipitation changes, monitored by the percentage f goethite relative to total iron oxides, lead ice age extremes ith maximum aridity during ice growth and maximum preipitation during ice melt. Rapid climate changes over the mazon Basin may reflect shifts in the position of the Interropical Convergence Zone forced by northern hemisphere inolation at precessional (1/23,000 yr) and obliquity (1/41,000 r) frequencies. Variance in the orbital eccentricity bands 1/100,000 and 1/413,000 yr) may be explained by nonlinear mplification of insolation forcing at precessional frequencies. he early response of Amazon precipitation to insolation, head of high-latitude ice volume (dO) at all orbital freuencies, suggests that tropical aridity is part of the chain of vents leading to ice ages, rather than a response to glacier scillations. © 1999 University of Washington.