PALEO-GROUNDWATER IN NORTHWESTERN OHIO AND THE SIGNIFICANCE OF PLEISTOCENE RECHARGE IN NORTH AMERICA

Groundwater samples from wells on the contact between Pleistocene fill and the Antrim Shale in Fulton County, Ohio yield d¹⁸O values much lighter than present day average precipitation (-14.5 vs -7.5‰). We have interpreted this water to be in part "paleo" in nature, having been recharged during the time of the last glacial retreat. These isotopic values can be interpreted in two ways. Using the current relationship between the d¹⁸O of precipitation and Greenland Ice Sheet air temperature, a mean annual temperature of ~-2°C is predicted at the time this water recharged. By assuming an even lighter Laurentide Ice Sheet value of -28‰, these groundwaters also could be a mixture of two thirds modern recharge and one third ice sheet meltwater. A review of the literature indicates that our observation is not unusual for the mid-portion of the North American continent. Older studies have observed either Pleistocene age waters or mixtures of glacial melt and more modern recharge in Illinois, Iowa, Missouri, North Dakota, Ontario, Manitoba and Saskatchewan. More recent studies have made similar observations in Michigan, Nebraska, and the Northwest Territories, Canada. The extent of these "paleo" waters will be discussed in terms of water resource management and the potential long-term extraction of these waters.