Isotopic fingerprints of paleoclimates during the last 30,000 years in deep confined groundwaters of southern India

Isotopic and geochemical evidence of paleoclimates, especially for the last glaciation, has been obtained from deep confined groundwaters of southern India. The delta(13)C, delta(18)O, chloride, and deuterium analyses of groundwaters show distinct excursions inferred to be related to climatic variations. The arid climatic episode associated with the last glaciation (18,000 +/- 2000 yr B.P.) is conspicuously identified by signatures of relatively enriched delta(13)C (-10 to -12 parts per thousand PDB) and delta(18)O (-5.3 to -4.8 parts per thousand SMOW) values, and high chloride concentration (80 to 160 mg/l). The transition from an arid to humid period ca. 12,000-8000 yr B.P. is shown by a decreasing trend in the delta(13)C (-9.5 to -17 parts per thousand) and delta(18)O (-4.5 to -6.3 parts per thousand) contents of groundwaters. The late Holocene (since 4000 yr B.P.), marked by a more humid but unstable climate, is identified by further depletion of delta(13)C (-13 to -20 parts per thousand) and delta(18)O (-5.2 to -6.3 parts per thousand). Similar variation between delta(18)O and chloride values in confined groundwaters further demonstrates two distinct climatic excursions (arid and humid) governed by the "amount effect." This is the first time that isotopic and geochemical signatures related to changing paleoclimates have been identified in the confined groundwaters of the southern Indian landmass. (C) 1998 University of Washington.