Seasonal formation of ikaite (CaCO2 center dot 6H(2)O) in saline spring discharge at Expedition Fiord, Canadian High Arctic: Assessing conditional constraints for natural crystal growth

Spring discharge at Expedition Fiord (Pollard et al., 1999) on Axel Heiberg Island in the Canadian High Arctic produces a variety of travertine forms in addition to a diverse collection of mineral precipitates. This paper foc uses on clusters of thermally unstable crystals believed to be the mineral ikaite (CaCO3. 6H(2)O) growing seasonally along two spring outflows at Colo ur Peak. This form of calcium carbonate mineral occurs along small sections of discharge outflow as white euhedral crystals up to 0.5 cm in length. Di fficulty in sampling, storage and transport of the samples for analysis has hampered attempts to confirm the presence of ikaite by X-ray diffraction. However, various field observations and the remarkable instability of these crystals at normal ambient temperatures strengthens our argument. This pap er provides a description of these particular CaCO3. 6H(2)O crystals and th eir environmental surroundings, and attempts to determine the validity of i kaite precipitation at this site by theoretical geochemical modeling: these results are compared with other reported observations of ikaite to both un derstand their occurrence and help delineate their geochemical characterist ics. It is believed that the restrictive combination of spring water chemis try and long periods of low temperatures characteristic of arctic climates are necessary for ikaite growth at this site. The fact that ikaite is not f orming at a second group of saline springs 11 km away allows us to more spe cifically outline conditions controlling its presence. Copyright (C) 2001 E lsevier Science Ltd.