Abstract
The last glacial period can be identified in groundwater globally in hydrochemistry and groundwater turnover. To illustrate this, three examples representing very different conditions are presented here, two from India and one from the Nordic countries. The last glacial period resulted in a 125 m lowering of the sea level below present level and the return to the same level within a relatively short geological time span. The low sea water level at Last Glacial Maximum (LGM) induced, in combination with variations in the SW monsoon, recharge of coastal aquifers here exemplified by the Tertiary aquifers in Kerala. The sea level lowering before LGM and its rapid subsequent recovery after LGM has caused different sedimentation conditions resulting in more oxidised Pleistocene sediments compared to Holocene sediments. This has affected the redox conditions and resulted in mobilisation of arsenic in groundwater in the Holocene strata notably in the Bengal delta and upstreams in the Ganga valley.
In the Nordic countries there was a 2.0-2.5 km high load of ice on the land. The result of the melting is seen in land uplift, which is still active to this day. The connections between the Baltic Sea and the ocean via the North Sea has varied during the postglacial period resulting in brackish and fresh water conditions making their imprint in the hydrochemistry and turnover of the groundwater. A common feature is seen from both regions in the form of the Na-HCO3 type of groundwater formed during fresh water flushing of a formerly saline aquifer. Along some shorelines there are reducing environment similar to those in India but the main manifestation is acid drainage as a result of slow land uplift and drainage for agriculture.
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