THE PALAEOHYDROLOGY OF COASTAL AQUIFERS OF EUROPE

Geochemical, isotopic and hydrogeological data are brought together on coastal palaeo-groundwaters across Europe in a transect from the Baltic to the Canary Islands. Interpretations are made in relation to past climatic and environmental conditions as well as extending and challenging concepts about the evolution of groundwater near the present-day coastlines. Freshwater of high quality originating from different climatic conditions to the present day and when the sea level was much lower is found at depth at several locations beneath the present coast. The implications of the scientific results for management of aquifers in European regions are considered.

An age gap can be recognized in some aquifers which indicates that no recharge took place at the time of the last glacial maximum (LGM). This indicates that although these areas were free of ice cover, sealing due to permafrost was effective. Groundwaters from Estonia have d¹⁸O values of approximately -22‰, demonstrating that recharge took place directly beneath the Scandinavian ice sheet during the LGM. Noble gas recharge temperatures supported by stable isotopic data provide convincing evidence in aquifers from northern Europe that recharge occurred during cooler climates prior to the LGM and that recharge temperatures were some 6°C colder than at the present day.

In southern Europe the radiocarbon ages indicate continuity of recharge through the LGM. Noble gas recharge temperatures in the Aveiro Cretaceous aquifer also indicate that atmospheric cooling of 5-6°C occurred before and during the LGM. However, in contrast to northern Europe, an en-richment in d¹⁸O of around 0.6‰ is found in the late Pleistocene recharge waters. This is consid-ered to reflect the enrichment in the Pleistocene ocean water as well as the constancy in the source of moisture from the Azores region of the Atlantic as at the present day. The overall results empha-size that the stable isotope signal in palaeowaters may either reflect the source or the temperature of the precipitation.