Isotopic methods and their hydrogeochemical context in the investigation of palaeowaters
H. H. Loosli, W. Aeschbach-Hertig, F. Barbecot, P. Blaser, W. G. Darling, L. Dever, W. M. Edmunds, R. Kipfer, R. Purtschert, K. Walraevens, 2001. "Isotopic methods and their hydrogeochemical context in the investigation of palaeowaters", Palaeowaters in Coastal Europe: Evolution of Groundwater since the Late Pleistocene, W. M. Edmunds, C. J. Milne
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Isotope and geochemical techniques are the primary way in which the residence time, recharge conditions and subsequent evolution of palaeowaters can be determined. Isotopic species and noble gas concentrations are used as residence time and palaeoclimate indicators. Among the former, 14C is pre-eminent in late Quaternary studies because of an age range which covers the Pleistocene–Holocene transition. However, its use is constrained by frequent difficulties in determining the dilution of dissolved 14C due to water–rock interaction. A combination of 14C data with 226Ra and 4He results may be useful for Holocene waters but they can also be used to validate the carbon systematics assumed for 14C dating. For waters beyond the range of 14C dating, 81Kr, 36Cl, 4He and chemical tracers can be applied.
Stable isotope ratios and noble gas concentrations primarily reflect climatic conditions at the time of recharge. While the noble gases provide absolute values for recharge temperatures, stable isotopes are only relative indicators that vary regionally. The PALAEAUX programme has examined these aspects in some detail by looking at the δ18O shift between Pleistocene and Holocene waters on the European scale, and by calculating δ18O/ΔT ratios from δ18O v. recharge temperature plots for aquifers at different distances from the Atlantic Ocean. Indications are that the more positive δ18O value of ocean water during the Pleistocene dominates in the more westerly European countries over the negative δ18O shift during cooler conditions. There are also indications that air-mass circulation during the Pleistocene was similar to the present day.
The evolution of a palaeowater can best be studied by measuring chemical tracers; this is possible in freshwater aquifers, where a clear trend of geochemical reactions is observed, and in freshening marine aquifers. Chemical and isotopic tracers can also be used to study the movement of the front between palaeowater and younger components that must be identified in coastal aquifers to guarantee a sustainable water use.
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Palaeowaters in Coastal Europe contains 17 contributions from an international array of authors. They discuss the history of groundwater evolution during the late Pleistocene in the coastal areas of Europe from the Baltic region to the Iberian peninsula and the Canary Islands. Geochemical and geophysical techniques for evaluating palaeowaters are reviewed. The focus of the book is on changes in the hydrogeological regime during the Quaternary and their impacts on groundwater movement and chemistry in European coastal aquifers.
The work summarized in the papers was carried out by a partnership of European scientists under the auspices of the PALAEAUX project, an EC initiative. Researchers from the fields of hydrogeology, geochemistry, isotope hydrology and Quaternary studies attempted to reconstruct the most probable movement of groundwater in the study area over the past 100 000 years and its response to climatic events of global significance during the last glacial cycle. The results of this work, summarized in this volume, allow a better understanding of the water resources found at and near the coastlines of northern and western Europe. During times of lowered sea level, it appears that groundwaters were replenished to depths greater than occur at the present day. These pristine freshwater reserves are an irreplaceable asset. Their location at coastlines where populations and water demands are high and often seasonal means that they need careful management to avoid over-exploitation or contamination. The inevitable conflicts that this resource management creates are discussed.
Palaeowaters in Coastal Europe: evolution of groundwater since the late Pleistocene will be of interest to Quarternary scientists, hydrogeologists, marine scientists engaged in coastal research and those involved in environmental science and the management of groundwater assests.