HOLOCENE MEGA-DROUGHTS IN THE CENTRAL ATACAMA DESERT, CHILE

Mega-droughts can have a severe impact on water and environmental resources, biological communities, and human populations. The response of geomorphic systems to mega-droughts may be extreme, affecting such hazards as landslides, flooding, and erosion. The availability of water resources in the hyperarid Atacama Desert of Chile is particularly critical in sustaining human populations and supporting the enormous local mining industry, while hopefully not having severe impacts on biological communities. In many semi-arid environments, the frequency and magnitude of mega-droughts can be reconstructed with dendrochronology. In these regions, the history of mega-droughts is then used to assess the synoptic climatic controls leading to mega-droughts and predict future mega-droughts. In truly arid lands, however, it is generally not possible to use dendrochronology to reconstruct mega-drought frequency due to a lack of trees. In-stream wetland deposits may provide the necessary chronology to reconstruct past mega-droughts. This study has investigated the potential of using well preserved in-stream wetland deposits to record a history of Holocene mega-droughts in the central Atacama.

The Río San Salvador of the central Atacama is an atypical stream catchment, with nearly all streamwater sourced from groundwater recharge. In-stream wetland deposits are remarkably well preserved in this watershed due to the lack of large erosive flood events. The alluvial stratigraphy of the watershed was determined by radiocarbon dating organic plant fragments preserved in cut-and-fill sequences. The dates obtained from radiocarbon ages have been used to reconstruct past cut-and-fill cycles, which at other localities have been shown to correlate with past mega-droughts. The alluvial stratigraphy has been compared with existing paleoclimate studies concerning vegetation histories and spring discharge deposits not influenced by fluvial processes. The results from this study may be used to help predict geomorphic response to these extreme events and help manage water resources in the Atacama Desert with regard to future climate change.