Middle to late Holocene initiation of the annual flood pulse in Tonle Sap Lake, Cambodia

Tonle Sap Lake, Cambodia, possesses one of the most productive inland fisheries in the world and is a vital natural resource for the country. The lake is connected to the Mekong River via the Tonle Sap River. Flow in the Tonle Sap River reverses seasonally, with water exiting the lake in the dry season and entering the lake during the summer monsoon. This flood pulse drives the lake’s biological productivity. We used Sr, Nd, and Pb isotopes and elemental concentrations in lake sediment cores to track changes in the provenance of deposits in Tonle Sap Lake. We sought to determine when the lake first began to receive water and sediment input via the Mekong River, which initiated flood pulse processes. The transition from a non-pulsing lake to the Mekong-connected system is marked by shifts to values of Sr/Sr, eNd, and Pb/Pb that are characteristic of Mekong River sediments. In addition, magnetic susceptibility increased and sediment elemental composition changed. Elemental (P) measures point to enhanced phosphorus loading and C/N and isotope ratios of bulk organic matter indicate a shift to greater relative contribution of organic material from aquatic versus terrestrial environments, coinciding with the initiation of flood pulse processes. On the basis of radiocarbon dating in two cores, we estimate the initiation of the annual flood pulse occurred between *4,450 and 3,910 cal year BP. Electronic supplementary material The online version of this article (doi:10.1007/s10933-010-9482-9) contains supplementary material, which is available to authorized users. M. B. Day J. H. Curtis G. D. Kamenov Department of Geological Sciences, University of Florida, Gainesville, FL 32611-2120, USA D. A. Hodell Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK M. Brenner W. F. Kenney Department of Geological Sciences and Land Use and Environmental Change Institute, University of Florida, Gainesville, FL 32611-2120, USA T. P. Guilderson Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, CA, USA L. C. Peterson Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA A. L. Kolata Department of Anthropology, University of Chicago, Chicago, IL, USA Present Address: M. B. Day (&) Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK e-mail: [email protected] 123 J Paleolimnol (2011) 45:85–99 DOI 10.1007/s10933-010-9482-9