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The Atacama Desert During the Medieval Warm Period
Nester, P.L., Gayo, E., Latorre, C., Jordan, T.E. and Blanco, N. 2007. Perennial stream discharge in the hyper-arid Atacama Desert of northern Chile during the latest Pleistocene. Proceedings of the National Academy of Sciences, USA 104: 19,724-19,729.

What was done
The authors studied fluvial terraces in the Pampa del Tamarugal (PdT) basin of the Atacama Desert of northern Chile, which contains widespread fossil wood, in situ roots, and well preserved leaf litter deposits indicative of perennial surface flow in now-dry channels, where streams once cut canyons in the desert's currently hyper-arid core.

What was learned
Based on radiocarbon dating, Nester et al. determined the approximate dates of the most important recharge events of these channels of the last 18,000 years, demonstrating that "there was enhanced stream discharge into the PdT during the time intervals of ˜17,750-13,750, ˜11,750, and ˜1,100-700 cal yr BP," noting that "groundwater must have been near the surface (<10 m) for Prosopis stands to have lived [there] between ˜1,100-700 cal yr BP." This latter "Medieval Climatic Anomaly (MCA)," as they go on to describe it, "is of opposite hydrological impact (wet) to that of coastal Peru (dry), where lithic concentrations in a marine core document diminished strength of El Niño events during the MCA (Rein et al., 2004)."

What it means
The wettest interval of the past 11,000-plus years in the hyper-arid core of the Atacama Desert (~AD 900-1300) coincides nicely with central portion of the mean timeframe of the global Medieval Warm Period, as can be seen by visiting the Interactive Map and Time Domain Plot of our Medieval Warm Period Project. This unique set of regional circumstances -- wet in the Atacama Desert of Chile and dry along coastal Peru -- is a strong indication of the dramatic but varied hydrological effects of the global Medieval Warm Period in this particular part of the world.

Rein, B., Luckge, A. and Sirocko, F. 2004. A major Holocene ENSO anomaly during the Medieval period. Geophysical Research Letters 31: 10.1029/2004GL020161.

Reviewed 22 October 2008