A Multi-Decadal Rock Magnetic Record of Monsoonal Variations during the Past 3,700 Years from a Tropical Indian Tank

We have explored the potentia1 of using magnetic susceptibility( χ_if) as a proxy for past rainfall variations in a tropical region, and also the potentia1 of tank-bed sediments from Southern India as a paleoarchive The 3,700-year rock magnetic record from Thimmannanayakanakere (14°12 N, 76°24 E), a smaH tank near Chitradurga town, Karnataka, exhibits considerable fluctudtions in χ_if Discountlng the possibilitestres of magnetite from biogenic and anthropogenic sources and of dissolutio of magnetic minerals, the χ_if signal must be related principally to rainfall in the tank-catchment There is a good correlation of χ_if with instrumental rainfall data (r = 0 65 for Peninsular India, r = 0 45 for Chitradurga Stationa)n d histoncally recorded rainfall events Presuming that χ_if variations are produced mainly by rainfall variations and that there was no signtficant human impact in the catchment and no slumping or bioturbatio of sediments we have reconstructed the paleorainfall profile for thc last 3,700 years for Chitradurga region The profile is chronologically constrained by two I4c dates Several events of drought and high rainfall, and onset of aridity are corretatable with similar events documented in speleothems from chfferent parts of india, a tree-ring from western India and lake sediments from Rajasthan We have thus shown that χ_if 1s a proxy for rainfall in tropical regions and that tank-bed sediments from tropical lndia are an important archive of paleorainfall/paleoclimate data.