Possible Solar Forcing of Late Holocene Mega-Droughts in India

Ashish Sinha [asinha@usc.edu], California State University, Dominguez Hills; K. G. Cannariato and L. D. Stott, University of Southern California; H. Cheng, University of Minnesota; M. G. Yadava, Physical Research Laboratory, India; R. L. Edwards, University of Minnesota; R. Ramesh, Physical Research Laboratory, India; I-B. Singh, Lucknow University, India; and H-C. Li, University of Southern California.

            Nearly one-quarter of the world’s population is affected by the seasonal rainfall brought by the Southwest Indian Summer Monsoon. As recently as the late 1960s, 1.5 million people in India died when the monsoon failed for three consecutive years. Climate model simulations indicate that multi-decadal monsoon failures are possible. Unfortunately, the instrumental record of Indian rainfall is too short to accurately characterize the frequency and length of monsoon failures for predictive purposes. To overcome this, we are using the oxygen isotope composition of growth layers in a suite of stalagmites collected from caves throughout India to reconstruct monsoon rainfall variability before the instrumental record began. Here we present an oxygen isotope record (δ18O) from a stalagmite collected from Dandak Cave located in central-eastern India. A preliminary chronology based on 230Th dates indicates that the high-resolution (~1 to 10 yr) δ18O record extends from the late Holocene to close to the present day. Century-scale intervals of heavy δ18O values indicate extended periods of reduced rainfall or mega-droughts in India. Furthermore, our δ18O record exhibits a striking resemblance to the Δ14C production rate record. Assuming century-scale variations in the Δ14C record are related to changes in solar luminosity, our record implies a possible causal link between reduced (enhanced) monsoon precipitation and lower (higher) solar luminosity. Our results from a core monsoon region of India appear to corroborate studies from other regions suggesting solar forcing of Indian/Asian Monsoon variability on decadal to centennial time scales through feedbacks associated with the global hydrologic cycle.