Past monsoon rainfall variations in peninsular India recorded in a 331-year-old speleothem M.G. Yadava, 1 * R. Ramesh 1 and G.B. Pant 2 ( 1 Physical Research Laboratory, Navrangpura, Ahmedabad-3800 09, India; 2 Indian Institute of Tropical Meteorology, Pune-411 008, India) Received 13 October 2002; revised manuscript accepted 12 June 2003 Abstract: An actively growing stalagmite collected from a cave located in the hills of the Western Ghats in the Uttar Kannada District of Karnataka, India, has been studied for stable isotope ratios of oxygen and carbon, width of growth layers and grey-level changes. Distinct carbonate layers, alternate coarse and compact, are seen in cross-section. Each couplet of compact and coarse layer is found to represent a single year. A total of 331 such couplets has been counted, indicating that the stalagmite started growing in AD 1666 and continued until it was sampled. Stable isotope ratios of oxygen (d 18 O) and carbon (d 13 C) show variations ranging from 13.6 to 7.9% and from 2.7 to 1.6%, respectively. We have reconstructed past rainfall changes of the cave site using the ‘amount effect’ in d 18 O of rain. Speleothem d 18 O and instrumen- tal rainfall data from the associated climate subdivision show a significant correlation (r ¼0.62, decadal average). Several sharp spikes of enrichment and depletion in 18 O are indicative of the past deficiency and excess in rainfall. Most of the severe drought years recorded independently by meteorological observations are found registered in the stalagmite layers. During the 331-year-period, rainfall was highest at AD  1666 and lowest around AD 1900. The stalagmite-generated past rainfall record can serve as a reason- able proxy for testing monsoon models. Key words: Speleothems, annual layers, stable isotopes, rainfall, climate reconstruction, southwest monsoon, Western Ghats, India. Introduction In regions such as tropical India, major growth of speleothems occurs during the wet season (  southwest monsoon: June to September) when water is abundant (Yadava, 2002). Spe- leothem d 18 O is related to the d 18 O of the local precipitation and is also affected by the temperature of a cave during carbonate precipitation (Gascoyne, 1992; Lauritzen, 1995; Bar-Matthews et al., 1996). In the tropics it is found that d 18 O content of precipitation is inversely related to the amount of rainfall (Dansgaard, 1964; Rozanski et al., 1993; Fricke and O’Neil, 1999). In tropical caves, d 18 O of freshly deposited calcite layers on a growing speleothem is depleted with increasing pre- cipitation and temperature (Neff et al., 2001; Burns et al., 2002). Therefore, d 18 O of the speleothem layers are a proxy for the past variations of d 18 O of meteoric water and mean annual surface air temperature. Speleothem d 13 C depends upon type of vegetation (C3 or C4), dripping rate of water, bedrock dissolu- tion rate and seasonal variations in the soil pCO 2 in a complex fashion (Lauritzen and Lundberg, 1999; Genty et al., 2001). Radiocarbon content of the freshly precipitated carbonate on the speleothem surface is diluted by dead carbon of the bedrock, affected by the degree of exchange of dissolved CO 2 with the soil atmosphere (Genty and Massault, 1999). These can be taken into account (Mook, 1980; Williams et al., 1999), and if the dead carbon content is assumed to be constant through time, and if actively growing speleothems are collected to enable the calculation of the dead carbon proportion, then the radiocarbon dating method can be applied to assign a basic chronology to the cave deposits. Akalagavi cave Karst formations are known to exist in the Uttar Kannada District of the Western Ghats of Karnataka, India (Figure 1). The Akalagavi cave is located in a village called Ulvi; a number of stalagmites and stalactites were found growing actively. One such stalagmite was collected and analysed in the present study. The cave has only one rectangular-shaped (approximately 12  4 m, poorly ventilated interior chamber. It occurs in a  40 m high hillock in a mountainous terrain and its entrance is located at  10 m height from the ground  Author for correspondence (e-mail: myadava@prl.ernet.in) The Holocene 14,4 (2004) pp. 517–524 # Arnold 2004 10.1191/0959683604hl728rp