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

Abstract

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.

Late-glacial to late-Holocene shifts in global precipitation δ<sup>18</sup>O

“…18 O late-glacial values across the majority of Europe. Measured 18 O late-glacial values are generally higher in western Europe (0.0 to −1.0 ‰ in Portugal, the United Kingdom and France) than in eastern Europe (−1.0 to −5.7 ‰ in Poland, Hungary and Turkey; Stute and Deak, 1989;Le Gal La Salle et al, 1996;Darling et al, 1997;Barbecot et al, 2000;Zuber et al, 2004;Galego Fernandes and Carreira, 2008;Celle-Jeanton et al, 2009;Varsányi et al, 2011;Samborska et al, 2013;Arslan et al, 2013). This spatial pattern of 18 O late-glacial values is consistent with enhanced isotopic distillation of westerlies during the late-glacial due to coolerthan-modern final condensation temperatures.…”

“…High magnitude, negative measured 18 O late-glacial values are located in Turkey and Georgia south and east of the Black Sea (−2.8 ± 1.0 to −5.7 ± 0.4 ‰; Fleitmann et al, 2009;Arslan et al, 2013;Melikadze et al, 2014). Westerly air mass trajectories distal to the Fennoscandian ice sheet topography may not have changed considerably since the lateglacial over western and central Europe (Rozanski, 1985;Loosli et al, 2001).…”

“…Speleothem records have 18 O late-glacial values close to +1 ‰ (Frumkin et al, 1999;Bar-Matthews et al, 2003). In northern Turkey, speleothem and groundwater separated by ∼ 150 km have measured 18 O late-glacial values that differ by ∼ 3 ‰ (speleothem 18 O late-glacial −5.7 ± 0.4 ‰ versus groundwater 18 O late-glacial of −2.8 ± 1.0 ‰; Fleitmann et al, 2009;Arslan et al, 2013Arslan et al, , 2015. While the locations of the groundwater and speleothem records differ, the compiled data suggest that groundwater and speleothem 18 O late-glacial values may capture different 18 O late-glacial values under similar climate conditions.…”

Global Isotope Hydrogeology―Review

“…In Europe, ∆δ 18 O late‐Pleistocene values are near zero along the Atlantic coast, as evidenced by ∆δ 18 O late‐Pleistocene records in Portugal's Sado Basin (Portugal; Fernandes & Carreira, ), and Aveiro Aquifer System (Portugal; Carreira et al, ), and in parts of the United Kingdom (Andrews, Edmunds, et al, ; Bath et al, ; Darling et al, ; Elliot et al, ). ∆δ 18 O late‐Pleistocene values decrease eastward to reach minimum values close to –3‰ in the Hungarian Great Plain (Stute & Deák, ), Pannonian Basin (Hungary; Varsányi et al, ), and northern Turkey (Arslan et al, ). The eastward decline in δ 18 O late‐Pleistocene values (Figure ) has been interpreted as an indication that mesoscale atmospheric circulation patterns remained largely unchanged between the late‐Pleistocene and late‐Holocene (Rozanski, ).…”

Analysis of groundwater dynamics in the complex aquifer system of Kazan Trona, Turkey, using environmental tracers and noble gases

“…These previous studies based on hydraulic and hydrochemical data have been unable to characterize the flow and mixing processes in detail. In a recent study, Arslan et al (2013) discussed climate change from the late Pleistocene to the Holocene by using environmental isotopes (δ 18 O, δ 2 H, δ 13 C, 14 C) and noble gas thermometry. They concentrated on the tracer data obtained from the deep groundwater system and used the data from the shallow aquifer only to compare modern recharge conditions to those in the past.…”