DYNAMICS OF PALEORECHARGE IN A DEEP CONFINED AQUIFER SYSTEM USING NOBLE GAS, 14C AND STABLE ISOTOPE TRACERS

Noble gas, stable isotope and ¹⁴C age data were collected along the flow path from municipal wells located in northeastern Wisconsin at a latitude ~200 km from the terminus of the last glacial maximum. ¹⁴C ages that increase to a maximum of 19,700 , along with stable isotope and geochemical trends indicate a clear demarcation between subglacially recharged and postglacially recharged portions of the aquifer. δ¹⁸O derived temperatures fall to levels as low as -5.6 ºC in waters recharged during the last glacial period. In contrast, noble gas temperatures remain constant near +2 ºC. This, in conjunction with large amounts of excess Ne (ΔNe = 60%-107%), and a noble gas fractionation pattern that does not match glacial ice itself is interpreted to be the result of surface meltwater recharging the aquifer through actively deforming moulins. This is in contrast to earlier work performed near the ice terminus in which the subglacially recharged water was found to contain very little glacial meltwater. Noble gases are a useful tool in the study of recharge in glacial terranes that is controlled by highly variable factors involving ice advance and retreat as well as permafrost formation and ice-induced pressure heads. Implications important to glacial movement in general and the occurrence of periodic glacial surges will be discussed.