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

We present a palaeoclimate record for northern South America, extending fro m the latest Pleistocene (similar to 12600 C-14 yr BP) to present. Climate reconstruction for the Valencia Basin, Venezuela, was based on sediment geo chemistry and delta(18)O records from ostracod and gastropod shells in a 56 8 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, permanentl y 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. Durin g 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 mois ture availability at this time may have been caused by increased intensity of the annual cycle (with wetter wet seasons and drier dry seasons), a resu lt 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 y r BP, are indicated in the oxygen isotope and calcium carbonate records. Si nce similar to 3000 C-14 yr BP, water level in Lake Valencia has been dropp ing.