Climate change in the Lake Valencia Basin, Venezuela, ~12600 yr BP to present

We present a palaeoclimate record for northern South America, extending from the latest Pleistocene (~12600 14 C yr BP) to present. Climate reconstruction for the Valencia Basin, Venezuela, was based on sediment geochemistry and δ 18 O records from ostracod and gastropod shells in a 568 cm sediment core. Sediment chronology was established by AMS 14 C dating of terrestrial wood fragments. From ~12600 to ~10000 14 C yr BP the Valencia basin was drier than present and the coring site, now under 9.4 m of water, was only intermittently wet. After ~10000 14 C yr BP, moisture availability increased and lake level rose, permanently covering the core site. From ~10000 to ~8200 14 C yr BP, Lake Valencia was hydrologically closed and the isotope records reflect pronounced variability in the ratio of evaporation to precipitation. During the wetter early to middle Holocene (~8200 to ~3000 14 C yr BP), lake level was high and water was lost to outflow. Greater moisture availability at this time may have been caused by increased intensity of the annual cycle (with wetter wet seasons and drier dry seasons), a result of large, orbitally driven differences in seasonal insolation. Two brief periods of lower lake level, at ~7000 and ~3300 14 C yr BP, are indicated in the oxygen isotope and calcium carbonate records. Since ~3000 14 C yr BP, water level in Lake Valencia has been dropping.