(ESH) Paleoenvironmental Change in the Atacama Desert During the Late Quaternary: Evidence from Middens and Paleosprings

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Fossil rodent middens and paleospring deposits at key sites along a 1500-km transect in northem Chile/southern Peru will be used to reconstruct late Quaternary vegetation and climate histories in the Atacama Desert. There are several advantages to studying these deposits in the Atacama Desert: 1) unlike lake records, middens and spring deposits contain abundant vascular plants that suffer no "hard water" effects in 14 C dating; 2) rainfall seasonality can be inferred from midden occurrences of plant taxa tethered to either summer or winter precipitation; 3) the lower elevational limits of most Atacama plants reflect local precipitation (and not growing-season temperature), whereas water levels in springs reflect regional snowpack in the high Andes; 4) both middens and spring deposits are ubiquitous and preserve a regional history of vegetation and water levels along the upper margins of the Absolute Desert. Carbon isotopes in soil carbonates also will be analyzed and relict drainage networks in parts of the Absolute Desert that might have experienced periods of sustained rainfall and vegetation expansion will be mapped.Three key areas affected by different synoptic climatologies will be sampled, and asynchronous climate histories are expected. Middens and spring deposits near Arequipa, Peru (16.5 S) will allow the proponents to track changes in summer precipitation just 200 km west of Lake Titicaca. Sites near Copiapo, Chile (27 S), 600 km north of Santiago, should isolate variations in the strength of extratropical winter precipitation. The central sites near Calaina, Chile, straddle the Tropic of Capricorn (23.5 S) and will reveal the interplay between tropical and extratropical rainfall belts. The proposed research will help refine current understanding of the nature and timing of late Quaternary climate change, and its hydrological and ecological effects, in subtropical South America.