Studying imprints of climatic and environmental change in a regional aquifer system in an arid part of India using noble gases and other environmental tracers

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Temperatures estimated using dissolved noble gases in groundwater have played a major role in determining continental climate during the last glacial maximum, particularly for the tropics. Such tropical paleotemperature records are available from South America, Africa, and the Arabian Peninsula, but not from Asia. A major goal of the proposed study of an aquifer system in the North Gujarat - Cambay (NGC) region in a semi-arid part of western India is therefore to provide high-quality paleotemperature information from an area that has not been well studied so far.Recent research has shown that noble gas temperatures (NGTs) in semi-arid tropical regions may in part reflect the influence of changing humidity and vegetation conditions on soil temperature, and the ‘excess air’ component in groundwater may be a potential indicator of past changes of humidity. These important research issues shall be addressed in more detail in the proposed study. A major goal will be to see how the known changes of humidity in the NGC region are reflected in the excess air and NGT records.Together with supporting investigations using water isotopes and environmental dating tracers (14C, 3H-3He, CFCs, SF6), the study is also expected to provide information useful to sustainable exploitation of the regional aquifer system, in particular with respect to the recently discovered problem of fluoride contamination in the NGC region. The hypothesis that high fluoride concentrations are linked to arid climatic phases shall be tested by looking for corresponding variations of the excess air component. Furthermore, a possible connection between natural SF6 and high groundwater fluoride shall be investigated.