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Oslo: frost flowers create a mercury bouquet

Frost flowers, the delicate structures that form on the surface of fresh sea ice, have been implicated in mercury depletion events – the drop in atmospheric mercury levels at the poles in springtime. Now researchers have come up with a potential mechanism for how the flowers take up mercury.

Speaking at the IPY Oslo Science Conference, Jody Deming of the University of Washington, US, explained how she and her colleagues discovered microbes living in the frost flowers, the first indication that the structures can support organisms. It’s protective exopolymers secreted by these bacteria that absorb the mercury.

Deming doesn’t think that anyone had looked for microbiology inside frost flowers before because of their extreme conditions – low temperatures (frost flowers form at temperatures of less than –8 °C), high salinity due to the expulsion of brine as the sea ice freezes below, high ultraviolet levels, and a brief lifetime before being dispersed by wind or squashed beneath snow.

As part of Canada’s Circumpolar Flaw Lead project, the team found lots of frost flowers, with dendrites 3–5 cm long, on thin ice in December 2007 and January 2008. Epifluorescence spectroscopy revealed the presence of microbes. What’s more, when the team grew frost flowers in the laboratory it found that the saltier the frost flower, the more bacteria it contained. It seems that bacteria are forced out of sea ice as it freezes, alongside salt. “Bacteria are impurities just like brine is,” said Deming.

Exopolymer concentrations in the frost flowers were 26 times higher than in sea ice. These gelatinous substances are secreted by microbes to help protect them from dessication, freezing and heavy metals. The polymer binds to the metal; it’s this action that the researchers believe is causing frost flowers to adsorb mercury during depletion events.

A paper on the work is in press at Geophysical Research Letters.

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