Geochemical processes in a Mediterranean Lake: a high-resolution study of the last 4,000 years in Zoar Lake, southern Spain

High-resolution geochemical analysis of a 6-m-long sediment core from Zoar Lake, southern Spain, provides a detailed characterization of major changes in lake and watershed processes during the last 4,000 years. Geochemical variables were used as paleolimnological indicators and complement Zoar Lakes's paleoenvironmental reconstruction based on sedimentological and biological proxies, which define periods of increasing allochthonous input to the lake and periods of dominant autochthonous sedimentation. Chemical ratios identify periods of endogenic carbonate formation (higher Ca/Al, Sr/Al and Ba/Al ratios), evaporite precipitation (higher S/Al, Sr/Al ratios), and anoxic conditions (higher Mo/Al, U/Th ratios and Eu anomaly). Higher productivity is marked by elevated organic carbon content and carbonate precipitation (Mg/Ca). Hydrological reconstruction for Zoar Lake was based on sedimentological, mineralogical and biological proxies, and shows that lower lake levels are characterized by Sr-rich sediments (a brackish lake with aragonite) and S-rich sediments (a saline lake with gypsum), while higher lake levels are characterized by sediments enriched in elements associated with alumino-silicates (Al, K, Ti, Fe, trace and rare earth elements), reflecting fresher conditions. Geochemical indicators also mark periods of higher detrital input to the lake related to human activity in the watershed: (1) during the Iberian Roman Humid Period (650 BC-AD 300), around the onset of the Little Ice Age (AD 1400), during the relatively drier Post-Roman and Middle Ages (AD 800-1400), and over the last 50 years, due to mechanized farming practices. Heavy metal enrichment in the sediments (Cu and Ni) suggests intensification of human activities during the Iberian Roman Period, and the use of fertilizers during the last 50 years.Financial support for this study was provided by the Spanish Ministry of Science and Education (Projects GRACCIE CSD2007-00067, IBERLIMNO CGL2004-20236-E, CALIBRE CGL2006-13327-C04/CLI, Ministerio MARM 200800050084447 and CGL-2006-2956-BOS), an Andalusian Government Predoctoral Fellowship, and the Andalusian Government (PAI groups RNM-328 and RNM-179). We thank the LRC (University of Minnesota, USA), particularly Doug Schnurrenberger, Mark Shapley and Anders Noren, for making possible the 2004 expedition. Karin Koinig, Achim Brauer and Bernd Zolitschka provided constructive criticisms and suggestions. We also thank Mark Brenner for language editing. A. Moreno acknowledges funding from the European Commission’s Sixth Framework Program (Marie Curie Outgoing International Fellowships, proposal 021673-IBERABRUPT). F. Jiménez-Espejo acknowledges the Japan Society for the Promotion of Science (JSPS).Peer Reviewe