PALEOWETLAND DEPOSITS AS PALEOCLIMATE RECORDERS GLOBALLY AND IN THE ATACAMA DESERT

Paleowetland deposits are generally under-recognized and under-utilized archives of climate change. In general, desert wetlands are supported by spring discharge more than surface run-off, and they tend to develop instead of lakes either because the climate is too dry or deep hydrographic closure is lacking. Paleowetland deposits can be very sensitive but sometimes discontinuous recorders of climate change and are highly amenable to carbon-14 dating using vascular plant material or terrestrial mollusks. Our recent studies from the Atacama Desert illustrate many of these general features of paleowetland deposits. Paleohydrologic response to climate change in the hyperarid Atacama Desert is conspicuous, resulting in widespread fine-grained deposits with diatomites and delicately preserved vascular plant fossils. Collectively these deposits record a major wet period in the late Quaternary, which we term the Central Andean Pluvial (or CAP) event. CAP lasted from 15.9 to 9.7 ka and was interrupted by a brief but clear drop in the water table between 13.8 and 12.7 ka. This matches very closely the chronology of water-level changes in mega-lakes in the nearby Bolivian Altiplano. We tie these dramatic changes in effective moisture in the region to modulation of the local South American Monsoon by fluctuations in sea-surface temperature gradients (ENSO) in the Pacific Ocean.