DIAGNOSTICO

There are relatively few locations on the Earth where perennial springs exist under cold, arid atmospheric conditions, and in continuous permafrost settings. Fewer still are not related to volcanic hydrothermal activity, and therefore considered “cold springs” in the context of this study. Most springs on Earth feature carbonate or silica spring deposits, and relatively few precipitate sulfate minerals. In the Northern Hemisphere there are documented perennial cold springs in all three territories of the Canadian Arctic (Michel and van Everdingen, 1987; Pollard et al., 1999; Socki et al., 2002; Grasby et al., 2003), in Alaska (Sloan, 1985), Siberia (Yoshikawa et al., 2006), and on the Tibet Plateau (Wang and French, 1994). Relatively low temperature thermal springs have been documented in Svalbard (Reigstad et al., 2011). In the Southern Hemisphere there is at least one cold perennial spring in Antarctica (Burt and Knauth, 2003).

1.5.1 Mars analogue perennial cold springs in North America

Grasby et al. (2003) have reported supraglacial sulfur springs at Borup Fiord Pass, Ellesmere Island, Nunavut, Canada. Here, springs discharge from the surface of a glacier estimated to be 200 metres thick, form deposits of elemental sulfur, gypsum, bassanite, calcite, and the calcite polymorph vaterite, and release H2S gas. Spring pH ranges from

7.29 to 9.50, and temperatures range from 1.0 to 2.3° C at various outlets (Grasby et al., 2003; Gleeson et al., 2011). Evidence indicates the presence of sulfur metabolizing bacteria within the glacial system, and also suggests that elemental sulfur is due to oxidation of H2S, which in turn results from the reduction of sulfate from subsurface

anhydrite beds. Grasby et al. (2003) hypothesize that sulfate reduction and sulfide oxidation may be biologically mediated, like in the case of evaporite-associated bioepigenetic sulfur deposits in Poland (Niec, 1992). Also in Nunavut, an ice-dammed

lake adjacent to Fountain Glacier on Bylot Island fed a proglacial perennial spring, 50 m beyond the terminus of the glacier. Flow was first observed in 1991, but the lake

catastrophically drained in between 1996 and 1999, and the spring has not been observed since (Moorman, 2003).

Several seasonal and perennial springs have been reported in a region of continuous permafrost with karstic development, in and around the Mackenzie Valley and the Mackenzie and Franklin Mountains, west and southwest of Norman Wells, Northwest Territories, Canada. In some cases recharge water flows beneath the permafrost layer along karstic taliks, up to 500 m deep, before resurfacing at spring outlets. Perennial springs often contain significant NaCl, and have temperatures as high as 9° C (Hamilton and Ford, 2002; Caron et al., 2008).

At least 50 perennial springs have been mapped in coastal northeastern Alaska and northwestern Yukon Territory and are associated with carbonate rocks or Tertiary sediments. Some of the most studied springs include Shublik and Salderochit in Alaska (Sloan, 1985). Water temperatures generally range from 0 to 4 °C in the early or late winter to 4 to 11 °C in the summer, at individual outlets, and pH is near neutral or slightly basic. Most springs are freshwater, although a few are brackish (Craig and McCart, 1975). Perennial groundwater-fed springs are responsible for forming an icing on the upper Firth River in the British Mountains, northern Yukon Territory, Canada (Cardyn et al., 2007). An icing is a mineral-bearing ice deposits formed when

temperatures drop below the eutectic point of the solution in question (Heldmann et al., 2005). While some of the groundwater here is suprapermafrost in origin, a large

proportion is drainage from karst (Clark and Lauriol, 1997). Also in northern Yukon Territory, Lone Mountain Spring flows perennially, and cryogenically precipitates a “carbonate slush”, also associated with an icing (Socki et al., 2002).

1.5.2 Mars analogue springs outside of North America

The Svalbard Archipelago is home to thermal springs, which flow through continuous permafrost and discharge saline groundwaters rich in hydrogen sulfide and ammonium (Reigstad et al., 2011). A number of springs have been documented parallel to fault zones

and near extinct quaternary volcanoes, including the Troll, Jotun, and Gygre thermal springs in the northwest, and the Fisosen and Trollosen thermal springs in the southwest (Reigstad et al., 2011). The entire region experiences an elevated geothermal gradient. Fisosen and Trollosen springs discharge waters with temperatures of 15 °C and 6 °C respectively, and modeling indicates that the temperature of the deepest parts of the aquifer, below several hundred metres of permafrost, must be 600–800 °C (Jensen, 1998). Perennial springs have been documented in the continuous permafrost region around the Lena River in Siberia, Russia (Yoshikawa et al., 2006). Budong Quan “Unfrozen Spring” is a perennial spring in the Ke Ke Xi Li area of Qinghai province, China. It is set in relatively warm high-altitude permafrost of the Tibet Plateau (Wang and French, 1994).

Most streams and gullies in Antarctic dry valleys flow only during the summer, and form from top-down melting of snow and ice due to increased solar insolation (Head et al., 2007). However, Don Juan Pond in the dry Wright Valley flows year round from a deep confined aquifer, contains saturated calcium chloride brine, and is home to a variety of microorganisms (Siegel et al., 1979). Brines rich in calcium chloride can remain liquid down to or slightly below -53 °C, which is close to the average surface temperature of Mars (Burt and Knauth, 2003). This makes Don Juan Pond one of the best Mars analogues groundwater outflow systems on Earth (Burt and Knauth, 2003).

Of the perennial cold springs listed above, very few discharge acidic or saline water and deposit sulfate minerals. This study focuses on two spring sites located in the Canadian Arctic, in semi-arid deserts underlain by permafrost: the Golden Deposit, Northwest Territories, which discharges seeps of cold, acidic water and precipitates jarosite; and the springs on Axel Heiberg Island, Nunavut, which discharge cold, saline to hypersaline water and precipitate a variety of sulfates, carbonates, and halite.