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 grou ndwaters show distinct excursions inferred to be related to climatic variat ions. 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. 12,000-80 00 yr B.P. is shown by a decreasing trend in the delta(13)C (-9.5 to -17 pa rts 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 th ousand). Similar variation between delta(18)O and chloride values in confin ed groundwaters further demonstrates two distinct climatic excursions (arid and humid) governed by the "amount effect." This is the first time that is otopic and geochemical signatures related to changing paleoclimates have be en identified in the confined groundwaters of the southern Indian landmass. (C) 1998 University of Washington.