Palaeohydrogeological reconstruction of groundwater recharge during Late Weichselian in the Baltic Basin

• Main Authors: Mokrik, Robertas, Mažeika, Jonas
• Format: Article in Journal/Newspaper
• Language: Russian; Lithuanian; English
• Published: 2002
• Subjects: Oxygen isotope; Meltwater; Permafrost; Groundwater recharge; Modelling; Talik; permafrost
• Online Access: http://lsmu.lvb.lt/LSMU:ELABAPDB5638168&prefLang=en_US

Several hypotheses were framed to explain the low 5I8O values of groundwater in Estonian Homocline. Traces of depleted groundwater were found also in other parts of Baltic Basin near the shoreline. According to collected data and relevant publications, the 6I8O values of groundwater in most aquifers range from -7.7 to -13.9%o. However, the ground-water in Estonia in the Cambrian-Vendian aquifer system has a significantly lower 51SO values, which vary mainly from -18 to -22.5%e. The overlying Ordovician-Cambrian aquifer is also depleted by I8O, but, as a rule, the degree of depletion is several per-mil less than in the Cambrian-Vendian aquifer. The thickness of the depleted water in Estonia reaches 450 m. In Gotland Island (Sweden Homocline) at the same depths ground-water has significantly higher 8I8O values (from -5.7 to -6.1%o). To explain the isotope data on groundwater, we analysed a model of pre-Late Glacial permafrost environments, where the groundwater in the cryolite zone is hydraulically communicating with the lake and river systems through taliks. According to the model, penetration through valleys of isotopically depleted surface water related to a cold climatic cycle reached up to 500 m. The mixing processes provided a possibility of subglacial penetration of meltwaters and mixing them with the old Huneborg-Denekamp time groundwater through permafrost--free talik zones. Traces of this penetration were discovered only near the shoreline, where 8I8O values vary from -12 to -13.9%o and I4C is below 4%. On the territory of Estonian Homocline a hydraulically close connection via the Cambrian-Vendian aquifer between talik systems of the Gulf of Riga and the Gulf of Finland existed through the permafrost before Late Glacial, also through the subglacial recharge during the recessional Pandivere (12 ka BP) and Palivere (11.2 ka BP) phases, thus influencing groundwater recharge by isotopically depleted water.