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Climatic instability during the late Pleistocene has been reflected in the pattern of groundwater recharge. This report summarizes palaeoclimate knowledge during the late Weichselian in Europe. During this period the majority of northern Europe was covered by thick ice sheets and permafrost, preventing aquifers from recharging. In contrast, southern Europe was generally free of these palaeoclimatic features. Palaeoclimatic information has been combined with isotope data to better understand the palaeorecharge conditions and recharge timing across the European continent. The O and H relationship shows latitudinal plus climatic influences. Radiocarbon data show that while southern European aquifers have generally been recharged continuously during the last 40,000 years, northern European aquifers typically show a recharge gap during the Last Glacial Maximum. Areas that underwent continuous recharge during the entire late Pleistocene period can also be distinguished from areas where recharge to aquifers was prevented during the Last Glacial Maximum. Finally, several examples are presented of melt-water recharge or subglacial recharge. The identification of such diversity in the groundwater palaeorecharge in Europe is of great importance for modellers developing management schemes for groundwater resources. [ABSTRACT FROM AUTHOR]

Summary: The study was carried out in the northern part of the Aquitaine Basin extending in Southwest France. The basin has been intensively exploited for various purposes for many years. Although the geological context is well known, there are still some gaps in the knowledge about the hydrogeochemical regime, groundwater average residence time and the palaeohydrological conditions prevailing during the recharge period which would help to secure sustainable exploitation of the resources. Environmental isotopes (18O, 2H, 3H, 13C) together with radiocarbon were used to evaluate hydrochemical evolution, residence time and palaeorecharge conditions for Jurassic, Cretaceous and Eocene aquifers. Radiocarbon activity in the aquifers varies widely between 0 and 94pmc. After radiocarbon corrections the ages indicate both modern and old waters sometimes exceeding the limit for 14C dating. The Fontes and Garnier model is best adapted to the specificity of the carbonate system. The content in stable isotopes of water is varying between −7.7‰ and −4.9‰ for δ18O and −52.3‰ to −29.6‰ for δ2H. The wide ranges of stable isotopic values imply variable climatic conditions. A group of isotopically depleted samples was detected, indicating colder climatic conditions during the recharge. Radiocarbon ages calculation, together with isotopic signature, point out that the depletion in stable isotopic values fits the period between 20 and 15ka B.P. and therefore indicate the Last Glacial Maximum (LGM). According to the correction model, the transition from Pleistocene to Holocene would occur between 15 and 12ka B.P. Palaeohydrological data from the Northern Aquitaine Basin does not confirm a significant hiatus in the recharge history. The recharge conditions in South Europe seem to have occurred under discontinuous permafrost conditions as documented by many palaeoclimatological archives. This is in favour of an uninterrupted recharge of the confined aquifers of Northern Aquitaine Basin. Such information should be considered by modellers in their attempts to simulate the hydrogeological functioning of large confined aquifers on the very long time range. [Copyright &y& Elsevier]

Abstract: The Bohemian Cretaceous Basin represents a complex hydrogeological system composed of several aquifers with very favourable hydrogeological properties. These aquifers have been exploited for many years. The sustainability of such resources might be guaranteed by well organised water management, which requires a detailed knowledge about the functioning of the hydrogeological system. Although many efforts have previously been made to evaluate groundwater residence time, the many intricate geochemical processes complicate groundwater dating. The current study clarifies the functioning of this complex hydrogeological basin using hydrogeochemical and isotopic investigations. Chemical data and a combination of 13C and 14C isotopes within the Cenomanian and the Turonian layers indicate groundwater interactions with deep-seated CO2, rock matrix, surface waters and fossil organic matter. Very depleted δ13C values (average δ13C∼−13.4‰) suggest interactions with fossil organic matter, whereas enriched values account for the interaction with deep CO2 gas ascending from the upper mantle via the numerous faults and fractures, and also, to a lesser extent, from calcite dissolution. Geochemical processes that take place in the system cause a clear depletion in 14C that greatly complicates groundwater residence time evaluation. Different dilution correction models have been applied considering the different C origins. The stable isotope content, mainly 18O values, indicates both the contribution of modern precipitation and the partial infiltration of palaeowaters during colder climatic conditions from the end of the Pleistocene. The apparent 14C groundwater ages range from modern to 11.1ka BP, which suggests some post glacial infiltration from melting ice sheets. Finally, all the acquired information was used to propose a conceptual model of C origin within the basin. [Copyright &y& Elsevier]