Environmental isotopes and noble gases in the deep aquifer system of Kazan Trona Ore Field, Ankara, central Turkey and links to paleoclimate

Environmental isotopes and noble gases in groundwater samples from the Kazan Trona Ore Field are studied to establish the temperature change between the Holocene and the late Pleistocene. Noble gas temperatures (NGTs) presented in this study add an important facet to the global paleotemperature map in the region between Europe and North Africa. The groundwater system under investigation consists of three different aquifers named shallow, middle and deep in which δ¹⁸O and δ²H vary from -8.10% to -12.80% and from -60.89% to -92.60% VSMOW, respectively. The average isotopic depletion between unconfined and confined parts of the system is -2.5% in δ¹⁸O and -20% in δ²H. It is not possible to explain this depletion solely with the elevation effect. Recharge temperatures derived from dissolved atmospheric noble gases reflect the current average yearly ground temperatures (13°C) for samples collected near the recharge area but are 3 to 8°C lower than today's temperatures in the deep aquifer system. Low ¹⁴C activities and high He excesses in the confined parts of the aquifer system suggest that the water in the deep aquifer was recharged during the last Pleistocene under considerably cooler climatic conditions.