Permafrost Conditions Near Two Water Storage Facilities on Baffin Island, Northwest Territories.

Cryostratigraphic and geochemical data obtained from 2 ice exposures at the cavity site are examined in detail to determine the origin of the ice. A thaw unconformity separates the ice-rich core of the moraine from overlying ice-poor sediments. Pore ice samples below the thaw unconformity are more conductive, have higher Na^+ and Ca^{++} concentrations and are depleted in ^{18}O and ^2H relative to pore ice above the thaw unconformity. Cryostratigraphic observations, changing cation ratios and the slopes of regression lines fit to the isotopic data suggest that ice within the core of the moraine is composed of Wisconsinan aged regelation ice. Ground ice observed at the two reservoir sites differs substantially. Several small ice wedges were exposed within raised deltaic sands and gravels during construction of the Pangnirtung reservoir. Two distinct levels of ice wedges occur. Thaw unconformities above some of the wedges and secondary growth veins above other wedges indicate periods of both permafrost degradation and permafrost aggradation at the site. Ice wedges are thought to have formed following emergence approximately 8700 years BP. Segregated ice lenses and several frost blisters occur at Water Supply Lake near Pond Inlet. The segregated ice occurs in the bed of the lake and has much higher cation concentrations, and more negative delta^ {18}O and delta^2 H values than frost blister ice. Isotopic concentrations for the frost blister ice indicate multiple growth phases under both open and closed system freezing. A cryostratigraphic model of ground ice development is constructed from field observations for periods following deglaciation, and after various stages of dyke construction. Ground thermal regimes at both water storage facilities are influenced by changing climate, construction activities and fluctuating water levels. Ground temperatures at Pangnirtung are warmest, but show a pronounced cooling trend with time, immediately beside the water body. This is thought to be caused by decreasing water levels toward the end of the record. Ground temperatures within the new dyke at Pond Inlet show that it froze during the winter of 1989 and has remained frozen ever since. These observations suggest that the design of the dyke is well suited for use at other sites in areas of similar climate. (Abstract shortened by UMI.).