RECORDS OF LATE PLEISTOCENE AND HOLOCENE CLIMATIC CHANGE CONTAINED IN EUROPEAN COASTAL AQUIFERS

Coastal aquifers retain dramatic evidence of rapid sea level rise during the early Holocene. Geochemical, isotopic and hydrogeological information on European coastal groundwaters from the Baltic to the Canary Islands are interpreted 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. Groundwater movement beyond the present coastline as well as emplacement on-shore to greater depths (up to 500m) than allowed by the present day flow regime has occurred and offshore freshwater reserves are inferred in some coastal areas. Recharge is shown to have been more or less continuous during the past 100ka, even beneath ice masses, as demonstrated by groundwaters from Estonia, having δ18O values of approximately -22‰. Elsewhere, however (UK and Belgium) an age gap can be recognized indicating that no recharge took place at the time of the last glacial maximum (LGM). Devensian recharge temperatures (soil air temperatures) were some 6°C colder across Europe compared with the present day.

The development of aquifers in Europe during the past 50–100 years by abstraction from boreholes has generally disturbed flow systems that have evolved over varying geological timescales and especially those derived from the late Pleistocene and Holocene. Hydrogeophysical logging has demonstrated time and quality-stratified aquifers resulting in mixed waters which are produced on pumping. A range of specific indicators including 3H, 3H/3He, 85Kr, CFCs, as well as pollutants have been used to recognize the extent to which waters from the modern (industrial) era have penetrated into the aquifers, often replacing the natural palaeogroundwaters.