Abstract

Many different proxy records including paleowetland deposits, lakeshore terraces, glacial features, rodent middens and plant macrofossil deposits have been used to reconstruct paleoclimate in the world’s arid regions. These records have provided important qualitative information on the extent, timing, and intensity of past climate events (such as major pluvial events) but quantitative records are much more difficult to obtain. The Atacama Desert is an extreme, hyperarid environment in the Southern Hemisphere that extends over most of northern Chile and southern Peru. The Atacama spans summer rainfall regimes in the north to winter rainfall regimes south of 26-28°S. Thus, the Atacama Desert is an ideal region for studying past shifts and intensities of both tropical (summer) and subtropical (winter) rainfall belts. In this poster, we advance the use of ashy chinchilla rat (Abrocoma cinerea) fecal pellets from rodent middens collected in the central Atacama Desert of northern Chile as a quantitative proxy of rainfall. We subsampled a set of seven modern middens from 18–25° S and 1540–3755 masl. Modern A. cinerea middens (defined as being either active or with 14C dates <100 BP) were used for calibration. They had to be collected away from present or past sources of water, ensuring that local rainfall was the only source of water in the vicinity. The diameter of the largest pellets (upper 20%) was measured and statistics were calculated. These results were compared to interpolated values of Mean Annual Temperature (MAT) and Mean Annual Rainfall (MAR) estimated at each midden site from both: (1) local climatic station records stored in the database of the Chilean Dirección General de Aguas and (2) a regional circulation model using PRECIS simulations. Our results indicate that the largest 20% of modern A. cinerea pellet diameters have a significant positive relationship (R2= 0.84, p<0.05) with MAR, whereas an inverse but non-significant relation is observed with MAT (R2= 0.38, p>0.05). Although precipitation clearly seems to be the most important factor behind variations in the largest pellet sizes, an inverse correlation with temperature is to be expected if pellet size is indeed a proxy for body size (Bergmann’s Rule). We apply these calibrations to a new quantitative paleoclimate record of past changes in rainfall in the central Atacama using A. cinerea pellet diameters and discuss the many caveats associated with such a record. The results of this research highlight the need for more research on the ecology and biogeography of these elusive, nocturnal rodents which could prove to be very sensitive to past climate change.