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 (similar to 12600 C-14 yr BP) to present. Climate reconstruction for the Valencia Basin, Venezuela, was based on sediment geochemistry and delta(18)O records from ostracod and gastropod shells in a 568 cm sediment core. Sediment chronology was established by AMS C-14 dating of terrestrial wood fragments. From similar to 12600 to similar to 10000 C-14 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 similar to 10000 C-14 yr BP, moisture availability increased and lake level rose, permanently covering the core site. From similar to 10000 to similar to 8200 C-14 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 (similar to 8200 to similar to 3000 C-14 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 similar to 7000 and similar to 3300 C-14 yr BP, are indicated in the oxygen isotope and calcium carbonate records. Since similar to 3000 C-14 yr BP, water level in Lake Valencia has been dropping.