Aufeis of the Firth River Basin, Northern Yukon, Canada: Insights into Permafrost Hydrogeology and Karst

Clark, Ian; Lauriol, Bernard

The 31-km2 aufeis ice sheet of the upper Firth River holds a wealth of information on groundwater hydrology in periglacial environments. Baseflow recession calculations, corrected for aufeis storage (12% of basin discharge), indicate specific groundwater recharge rates of up to 100 mm yr-1 (up to 50% of runoff), suggesting a significant proportion of drainage from karst. The upper Firth River aufeis is a composite aufeis, with discrete baseflow contributions from different watersheds. Since the late Pleistocene, annual growth of the aufeis has exerted a strong control on lateral erosion and the local river channel geomorphology. Two groundwater recharge processes are distinguished on the basis of carbonate geochemistry and δ13C: (1) Methanogenic groundwaters, with 14CDIC up to -3.3‰, are recharged saturated soils underlain by permafrost; conditions which support anaerobic consumption of dissolved organic carbon (DOC) and produce up to 700 μg-CH4 L-1 (calculated), and (2) Karst groundwaters, with 13C-depleted DIC, recharged through unsaturated soils and circulate through fissured talik in the carbonate bedrock. Most drainage from the region shows varying contributions of these two groundwaters, although a greater contribution from the methanogenic groundwaters occurs in north-facing watersheds. The δ13C values for cryogenic calcite precipitates in the ice indicate that the karst groundwaters are the major contribution to aufeis growth. The combined use of δ 13CDIC and geochemistry may be a useful tool to quantify methanogenesis in northern watersheds.

Aufeis of the Firth River Basin, Northern Yukon, Canada: Insights into Permafrost Hydrogeology and Karst

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