Philippe Mourguiart

Climate Changes in the Lake Titicaca Area: Evidence from Ostracod Ecology

The field of lake and wetland paleoecology has undergone recently significant changes. Quantitative statistical methods (transfer functions) have been developed to infer past limnological conditions. The large number of altiplanean lakes in the Central Andes, distributed over a hydrologically and climatically diverse area between 14 and 22° south, provide an ideal natural laboratory for this kind of approach. Changes in the water volume and chemistry of these aquatic environments, which result from their hydrological response to seasonal and long-term trends in the regional evaporation-precipitation balance are archived in the sediment records as characteristic biological signatures. The taxonomy and biogeography of several different groups of organisms have been studied in some detail, but relevant ecological studies have been done only on ostracods. This study attempts to reconstruct past environments of Lake Titicaca and adjacent lacustrine systems by using quantitative information about the response of ostracod communities to habitat heterogeneity and environmental variability, especially lake-level and water chemistry. The high-amplitude paleoenvironmental variations indicated by the transfer function developed have important implications for regional climate dynamics. In particular, the inferred high-amplitude lake-level fluctuations are attributed primarily to drastic changes in ITCZ displacements during the last 10,000 years.

Late Quaternary palaeohydrology of Lake Huinaymarca (Bolivia)

In lake Titicaca, the distribution of the modern ostracod fauna appears to be controlled by a combination of two factors: a) the equilibrium between carbonates and organic matter, b) the ionic composition of the lake water and its tributaries. Therefore, the Limnocythere-Pampacythere group generally predominates on an alkaline-carbonate lake floor. In parts of the lake receiving an NaCl input from tributaries, Cyprideis and Cyprinotus occur. These are generally absent elsewhere. The Candonopsis group is found in the deepest part of the lake.