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Dr Alan Channing

Hot spring environments and ecosystems through time
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Cryogenic opal-A is formed as waters erupt from a hot spring into environments characterised by sub-zero air temperatures. This process has been overlooked in previous investigations of the sedimentology of hot spring areas such as Yellowstone, Iceland and El Tatio in Chile all of which are subjected to either seasonal or daily freezing cycles. In all of these areas a considerable volume of sediment accumulating each year on sinter aprons and in geothermally influenced wetlands has passed through a freezing step prior to deposition.
I first became aware of the presence of such sediments during investigations of a small geothermal wetland at Porkchop Geyser, Yellowstone National Park. The strange morphology of some of the particles within this wetland appeared to be impossible to form during "normal" summer silica precipitation processes.
The breakthrough moment in my investigations of these particles came when I found images of the microstructure of sea ice. Resin impregnation of blocks of ice reveal a network of brine channels, veins and pockets that form as salt dissolved in the water prior to freezing is excluded from incorporation in forming ice crystals. In hot spring areas silicon is present in solution along with salt. It is also excluded from ice crystals. As it is present at supersaturated concentration it precipitates in the brine channel network.  

Hot spring environments in Yellowstone with hot spring ice and cryogenic opal-A sediments.

In 2006 I
 was awarded an Earth and Space Foundation Award that part funded my investigations of cryogenic mineral formation around terrestrial thermal springs.
The project funded was entitled -
Astrobiological implications of hydrosphere, cryosphere, biosphere interactions at Icelandic hot springs

Category: Using environments on Earth to understand other worlds / exobiology

Institution: Cardiff University, Edinburgh University.

Mineral depositing hot springs are prime astrobiological targets because on Earth hot springs support abundant microbial populations which are fossilized by minerals precipitating from their spring waters. Fossilization creates rocks with identifiable structural and/or molecular markers for biological activity which are durable over geological timescales. Increasingly, frozen environments (cryosphere) are also seen as potential havens of extraterrestrial life. This project aims to explore interactions at the interface between the biosphere, cryosphere and hydrosphere in a Mars-like setting. Martian hot spring systems are most likely to be “rooted” in basaltic crustal rocks, this would favour the formation of mixed silica, carbonate and iron oxide hot spring deposits at the Martian surface. Of Earths' major geothermal areas Iceland which has basaltic volcanism provides the closest analogue to this setting.

Specifically this project aims to:   

·  Establish by field observation the extent to which cryogenic conditions influence mineral precipitation processes at Icelandic springs and investigate processes that influence their formation and distribution.

·  Test the hypothesis that microbial fossilisation is associated with mixed mineral phases generated by cryogenic processes by collection of geothermal water samples, ice samples containing cryogenic precipitates and cryogenic sediments for analytical and microscopic investigations.

·  Test the idea that microbes may survive sequentially being immersed in hot spring water and then supercooled extremely saline water in brine channel environments by attempting to culture microbes from hot spring derived ice.

 Natural and synthetic cryogenic opal-A particles respectively collected from Yellowstone N.P. and created at Cardiff University.

Collecting cryogenic opal-A from beneath hot spring ice on the sinter apron of Strokkur Geyser, Iceland.