Response of a modern cave system to large seasonal precipitation variability Jessica L. Oster a,⇑ , Isabel P. Montan ˜ez b , Neil P. Kelley b a Department of Earth and Environmental Sciences, Vanderbilt University, United States b Department of Geology, University of California, Davis, United States Received 17 October 2011; accepted in revised form 27 May 2012; available online 7 June 2012 Abstract Speleothems are capable of providing information on the response of middle and low-latitude terrestrial environments to global climate change during the Pleistocene and Holocene. Multiproxy speleothem studies, however, have demonstrated that complex interactions can occur in cave settings between processes that are directly and indirectly related to climate change. Thorough and extended monitoring of modern cave environments is necessary in order to fully understand how each cave responds to these processes on seasonal and interannual timescales, and how environmental signals are preserved in speleo- them carbonate. Regular environmental monitoring began at Black Chasm Cavern in the Sierra Nevada foothills, California, during the winter of 2006–2007. Monthly measurements of cave air temperature, humidity, and pCO 2 in Black Chasm demonstrate that the cave is ventilated in the winter months, when cold, dense surface air sinks into the cave. Cave drip-water flow nearly ceases during the late summer and autumn, increases substantially during the winter and spring, and responds within hours to storm events during the height of the rainy season. Rainwater and drip water d 18 O and d 2 H are controlled by variations in surface air temperature and moisture source. While rainfall source influences rainwater isotopes through individual storm events, it has less influence on drip water isotopic composition due to mixing of recharge waters delivered by different rainfall events in the epikarst. Variations in drip water chemistry (d 13 C, Mg/Ca, and Sr/Ca) indicate that the greatest level of calcite precipitation upflow from the drip water collection site (prior calcite precipitation) occurs during the autumn (October–November) when drip rates are slow and cave air pCO 2 is low. The least prior calcite precipitation occurs during the summer (July–August) when drip rates are slow but cave air pCO 2 is at a maximum. While pCO 2 is a primary control on prior calcite precipitation during all seasons, the predominant influence of drip rate variability on prior calcite precipitation is evident when considering only those seasons (winter, spring, and autumn) characterized by low cave air pCO 2 . Thus, drip rate variability, and in turn rainfall amount, should provide the primary control on trace element variations ultimately captured in speleothem calcite. The isotopic and chemical variability observed in Black Chasm drip waters supports previous interpretations of speleothem paleo- climate proxy records from a nearby cave where such monitoring is not feasible. Observations of the modern cave environ- ment at Black Chasm provide a reference point for the interpretation of stalagmite proxy records from similar seasonal (Mediterranean) climates. Ó 2012 Elsevier Ltd. All rights reserved. 1. INTRODUCTION Speleothem geochemical proxy records have the potential to provide valuable archives of rainfall variability, atmo- spheric circulation changes, and vegetation response in low and mid-latitude continental environments and have con- tributed significantly to our understanding of hemispheric 0016-7037/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.gca.2012.05.027 ⇑ Corresponding author. E-mail address: jessica.l.oster@vanderbilt.edu (J.L. Oster). www.elsevier.com/locate/gca Available online at www.sciencedirect.com Geochimica et Cosmochimica Acta 91 (2012) 92–108