High-Resolution Record of Water-Level Changes in Lake Titicaca, Bolivia/Peru

temporal resolution must be both sufficiently extensive and Sediment cores collected from the southern basin of Lake Titifine-scaled to describe patterns that appear at the scale of caca (Bolivia/Peru) on a transect from 4.6 m above overflow level the processes of interest. When the affected processes are to 15.1 m below overflow level are used to identify a new centurycertain human activities, this criterion for fine-scale resoluscale chronology of Holocene lake-level variations. The results tion can be achieved by spatially defining the unit of study indicate that lithologic and geochemical analyses on a transect of as a lake and its drainage basin and temporally as the period cores can be used to identify and date century-scale lake-level of habitation by humans. Furthermore, the measurement and changes. Detailed sedimentary analyses of subfacies and radiocardescription of paleoclimate at a lake basin point will be even bon dating were conducted on four representative cores. A chronolmore valuable if it is imbedded in a spatially extensive web ogy based on 60 accelerator mass spectrometer radiocarbon meaof other point descriptions. surements constrains the timing of water-level fluctuations. Two methods were used to estimate the C reservoir age. Both indicate South America has a scarcity of sites with century-scale that it has remained nearly constant at Ç250 C yr during the paleoclimate data sets, yet is extremely important because late Holocene. Core studies based on lithology and geochemistry El Niño/Southern Oscillation events (ENSO) cause major establish the timing and magnitude of five periods of low lake economic hardships, the intertropical convergence zone level, implying negative moisture balance for the northern Andean (ITCZ) migrates over two-thirds of the surface area annualtiplano over the last 3500 cal yr. Between 3500 and 3350 cal yr ally, the vast Amazon basin is the largest remaining forB.P., a transition from massive, inorganic-clay facies to laminated ested area in the world (with important climatic and paorganic-matter-rich silts in each of the four cores signals a waterleoclimatic implications), and several civilizations have level rise after a prolonged mid-Holocene dry phase. Evidence of developed and collapsed on the continent. The Lake Titiother significant low lake levels occurs 2900–2800, 2400–2200, 2000–1700, and 900–500 cal yr B.P. Several of the low lake levels caca drainage basin and associated altiplano in the Perucoincided with cultural changes in the region, including the colvian and Bolivian Andes is an endorheic system that was lapse of the Tiwanaku civilization. q 1997 University of Washington. also the site of the Tiwanaku civilization. Nearby alpine glaciers, and the lake itself, contain paleoclimate records. Several previous studies have been done in the Titicaca INTRODUCTION watershed (Thompson et al., 1985; Wirrmann and Mourguiart, 1995; Abbott et al., 1997). In this paper we describe a finely resolved record of lake-level change driven by Highly resolved lacustrine records are useful for studying the mechanisms and effects of climate change. Spatial and climatic variability over the past 3500 yr, and in a compan-