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

利用地下水中溶解惰性气体估算的温度在决定末次极大期大陆气候方面发挥了重要作用，特别是在热带地区。这样的热带古温度记录在南美洲、非洲和阿拉伯半岛都有，但在亚洲没有。因此，对印度西部半干旱地区北古吉拉特邦-坎贝（NGC）地区含水层系统进行拟议研究的一个主要目标是，从一个迄今尚未得到充分研究的地区提供高质量的古温度信息。最近的研究表明，半干旱热带地区的惰性气体温度（NGTs）可能在一定程度上反映了湿度和植被条件变化对土壤温度的影响，地下水中的“过量空气”成分可能是过去湿度变化的潜在指标。这些重要的研究问题将在拟议的研究中更详细地讨论。一个主要的目标是观察NGC区域已知的湿度变化如何反映在过量空气和NGT记录中。与使用水同位素和环境测年示踪剂（14C、3H-3He、CFCs、SF6）的辅助调查一起，该研究预计还将为区域含水层系统的可持续开发提供有用的信息，特别是关于最近在NGC区域发现的氟化物污染问题。应通过寻找过量空气成分的相应变化来检验高氟化物浓度与干旱气候阶段有关的假设。此外，还应调查天然SF6与地下水高氟化物之间的可能联系。

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.