Hydroclimate variability during the last two millennia from the mudflats of Diu Island, Western India

Abstract

The climate variability over western India has been significantly influenced by the perturbations in the Indian summer monsoon (ISM) and thus, provides a crucial platform to investigate the paleomonsoon variations, weathering intensity, and sediment source. The mudflats of southern Saurashtra, western India are deprived of perennial rivers, but the region receives terrestrial contribution exclusively due to activation of seasonal rivers during the monsoon. In the present study, an attempt has been made to investigate the paleomonsoon and palaeoweathering using various geochemical proxies (detrital, productivity, redox, and weathering) on the mudflat sediment core of southern Saurashtra, western Gujarat. The core is chronologically constrained by 14C, 210Pb, and 137Cs dating techniques. The study suggests ISM strengthening during 2000–1800 cal yr BP with intermittent marginal ISM weakening during 1950–1970 cal yr BP and 1930–1890 cal yr BP associated with the reduced solar irradiance. Further, ISM weakening has been invoked during Dark Age Cold period (1800–1300 cal yr BP) and Little Ice Age (800–200 cal yr BP) interrupted by a marginal ISM strengthening during Medieval Warm period and the last two centuries witness climate warming. Based on historical rainfall data and Al2O3, an intermittent strengthening of ISM during 90–30 cal yr BP has been suggested while a gradual increase in the weathering intensity synchronous to the rise in sea surface temperature (SST) during the last 200 cal yr BP revealed the role of temperature on the intensity of chemical weathering in the study area. In spite of changes in the geochemical proxies as a function of ISM fluctuations, the palaeoweathering intensities has remained nearly consistent wherein the chemical weathering was less operative and accompanied by the deposition of texturally immature sediments. The sediments of Diu mudflat indicate mafic signatures thereby underscoring a major contribution of the Deccan basalts along with other variable sources.