Sr isotope and geochemical studies on Kaveri, Palar and Ponnaiyar rivers, southern India and 10Be isotope studies on Quaternary sediments of Kaluveli Lake, near Pondicherry, India

Abstract

The intensity of weathering is controlled by several parameters, such as, climate, lithology, hydrology, topography, physico-chemical and biological aspects. Deriving functional relationships between chemical weathering rates and their controlling parameters in present-day environments will help in correctly interpreting paleo-climate proxies. Globally, CO2, a greenhouse gas that exerts strong influence on climate, is consumed through photosynthesis and chemical weathering of silicate and carbonate rocks. The net global weathering process, atmospheric CO2 is converted to bicarbonate and balanced by a dissolved cation from the weathered bedrock, transported to the oceans by rivers. Over million-year timescales, the process of chemical weathering of the continents may shift considerable amounts of CO2 from the atmosphere to carbonate sediments via river runoff. Geochemical and Sr isotopic studies on river water will help to understand the chemical weathering, net CO2 consumption and Sr flux to the oceans. Such studies have been carried out on Ganga-Brahmaputra and Indus river systems draining Himalayas and Peninsular rivers, such as, Krishna and Narmada. Whereas, Peninsular rivers are not studied in detail. The conclusion drawn for the Himalayan river systems can not be generalized, because, of different controlling parameters. This study is focused on understanding the chemical weathering of southern granulites, Peninsular gneisses and other rock types that are exposed in the drainage basins of Kaveri, Palar and Ponnaiyar rivers. Sr isotope ratios and major ion abundance were determined on water samples of Kaveri, Palar and Ponnaiyar rivers, collected during NE monsoon of 2005 when there was unusually heavy rainfall and during pre-monsoon period, May-June 2006. As these rivers drain diverse Precambrian terrains, this study will help to understand chemical weatheringof various types of silicate rocks, their contribution to dissolve fluxes of elements to the ocean and net CO2 drawdown from atmosphere.