ALPINE LAKE RECORDS OF VENEZUELAN CLIMATE DURING THE LAST 1,000 YEARS

Tropical regions (30N-30S) are a substantial component of the climate system, covering 50% of the globe. They are an influential factor in both the global energy balance and hydrologic cycle, therefore climatic changes in the tropics can have global climate effects. Here we present preliminary results from a project which aims to reconstruct the Holocene climate history of the Venezuelan Andes on century to millennial timescales using multi-proxy analyses of lake sediment cores.

Evidence from three lakes with in the Cordillera de Merida, Venezuela constrains the timing of neo-glacial conditions in northern South America. Sediments from Laguna Mucubaji, located at 3500m a.s.l., record changes in clastic sediment input reflecting the establishment and fluctuations of glaciers in the watershed. The Mucubaji watershed has maximum elevations around 5000m while the existing glacial limit in the Cordillera is approximately 5200m. Although currently devoid of glaciers, the high elevations in the watershed suggest that small fluctuations in moisture and temperature could lead to the establishment of glaciers. Beginning around 700 BP, clastic sediment flux into L. Mucubaji increases 3-fold suggesting increased glacial activity, likely corresponding to a set of young moraines present in the watershed.

Sediment records from Laguna Blanca and Laguna Verdes Baja reflect changes in lake hydrology highlighting fluctuations of the regional moisture balance. Sedimentologic evidence from Laguna Blanca, a lower elevation lake, indicates relatively dryer conditions at the site during the middle-Holocene and a transition to wetter conditions from 900-600 BP. Older Laguna Blanca sediments are dominated by twigs and leaf litter while younger sediments are devoid of this material and are predominantly fine-grained laminated lake sediments. Sediment geochemistry and diatom species abundance from Laguna Verdes Baja, a periodically closed basin lake located at 4200m a.s.l., suggest changes in the hydrologic status of the lake beginning around 750 BP.

Sediment evidence from these lakes, along with other lake records from the Cordillera de Merida suggest that cooler and wetter conditions were responsible for glacial expansion during the last 1000 years.