Origin and formation of methane in groundwater of glacial origin from the Cambrian-Vendian aquifer system in Estonia

Late Pleistocene and Holocene groundwater flow history in the Baltic Artesian Basin: a synthesis of numerical models and hydrogeochemical data

“…Raidla et al ( 2012) used 14 C to date the meltwater intrusion to 14-27 ka ago, which is coeval with the advance and maximum extent of the Weichselian glaciation in the area (Kalm 2012). In addition, the isotopic composition of methane in the Cm-V aquifer system indicates that the annual air temperature when the methane formed was about -2 to -8 °C (Raidla et al 2019a). It supports the understanding that Pleistocene ice sheets advanced over areas where terrestrial vegetation had been only recently active and the infiltration of glacial meltwater happened mainly during the phase of ice sheet advance.…”

“…Our previous work on the Cambrian-Vendian aquifer system (CVAS), an important source of public water supply in northern Estonia, has provided compelling evidence that the aquifer has been strongly impacted by glaciations and recharged by glacial meltwater. The evidence can be summarized as follows: the groundwater has the lightest known oxygen isotopic composition in Europe (δ 18 O values as low as -23‰; Raidla et al 2019a), unexpectedly high gas concentrations, absence of 3 H and a low radiocarbon concentration (Vaikmäe et al 2001a;Raidla et al 2012;Vallner & Porman 2016;Pärn et al 2019;Vallner et al 2020). Our first noble gas analyses suggest that palaeorecharge took place at temperatures around the freezing point (Vaikmäe et al 2001a).…”

“…The results of the studies on the origin, geochemical evolution and age of groundwater in the aquifer systems of the northern BAB have been published in recent decades in a number of papers and dissertations (Mokrik 1997;Vaikmäe et al 2001aVaikmäe et al , 2001bVaikmäe et al , 2008Karro et al 2004;Marandi 2007;Raidla et al 2009Raidla et al , 2012Raidla et al , 2014Raidla et al , 2016Raidla et al , 2019aRaidla et al , 2019bRaidla 2010;Pärn et al 2016Pärn et al , 2018Pärn et al , 2019Gerber et al 2017;Suursoo et al 2017;Pärn 2018;Vallner et al 2020). However, several recent studies on the palaeowaters in the BAB have employed other meth odologies besides geochemistry and 14 C dating, which have been traditionally used for that purpose.…”

“…Jiang et al (2012) determined the isotope ratios 81 Kr/Kr and 85 Kr/Kr using the ATTA-3 instrument in the Laboratory for Radiokrypton Dating, Argonne National Laboratory. The origin and formation of methane in groundwater of glacial origin from the CVAS in the northern part of the BAB was studied using isotope analyses of methane (δ 13 C CH4 and δ 2 H CH4 ; Raidla et al 2019a). Finally, numerical models have been developed to assess palaeo-recharge under the Fennoscandian ice sheet and its impact on regional groundwater flow (Sterckx et al 2017(Sterckx et al , 2018Vallner et al 2020).…”

“…So, the noble gas composition of sampled wells does not allow determination of recharge temperature and an appropriate model to describe the data set has not been found yet. The analyses of the gas composition in groundwater samples also showed a rather high concentration of biogenic methane (Vaikmäe et al 2001a;Raidla et al 2019a). McIntosh et al (2012 have shown that shallow biogenic methane in the Illinois Basin (USA) was stimulated by subglacial recharge.…”