[M-IS08] Paleoclimatology and paleoceanography

[MIS08-05] Reconstruction of paleoclimatic signals from groundwater in large aquifers-a case study in Leizhou peninsula, Southern China

*Shaoheng Li¹, Jianyao Chen¹, Dioni Cendon², Florian Freundt³, Zongyu Chen⁴, Guomin Yang⁵, Shuang Xiao² (1.School of Geography and Planning, Sun Yat-sen University, Guangzhou, China, 2.Australian Nuclear Science and Technology Organisation, Kirrawee, Australia, 3.Institute of Environmental Physics, Heidelberg University, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany, 4.Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang, China, 5.Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, China)

Keywords:Paleoclimate reconstruction, Groundwater , Multiple tracers, Noble gases, Stable isotopes

The past is the key to the future, Knowledge of the paleoclimate is essential to understand the present climate and project potential future climate scenarios. Groundwater in aquifers, though as a low time-resolution archive, can provide valuable information regarding past climate change. In this study, 13 deep monitoring wells were chosen for water sampling during our first fieldwork in Leizhou peninsula, a (sub)tropical area in southern China. Multiple tracers (³H, ⁴He, ¹⁴C, ⁸¹Kr, ⁸⁵Kr) were applied for accurate groundwater dating and the concentration of noble gases dissolved in groundwater was measured for paleotemperature reconstruction. Stable isotopes (²H, ¹³C, ¹⁸O), major ions and other geochemical properties were also analyzed for these samples. According to the preliminary results, most groundwater samples’ age is located in the dating range of ¹⁴C and shows a relatively continuous record through the past 30,000 years. A possible recharge gap during LGM (Last Glacial Maximum) is identified and may indicate a quite cold and dry environment during this period in Leizhou peninsula. Paleotemperature revealed by the physically-based NGT (Noble Gas Thermometer) method shows that at least an environment temperature difference of 3.4 ℃ exists between the cold period and the present. A detailed comparison between NGTs, excess air (represented by ΔNe) and ¹⁸O indicates that the major controlling factor of stable isotopes (²H and ¹⁸O) in local groundwater might be the amount of precipitation rather than temperature, therefore the signals of ¹⁸O in groundwater can be interpreted as the change of moisture. Together with the NGTs, it is possible to reconstruct the paleoclimate information (including the climate state of warm/cold and wet/dry) through the groundwater archive in this study area. In addition, the groundwater dating results and recharge history revealed by this study can assist in local groundwater resource management and exploitation.