Let's cover the arctic ice with sooty forms of carbon ...

--- a great way to stop the ice melting and a good way to store carbon ?!


Spiky glaciers are slower to melt -


rying to save high-altitude glaciers? Then sprinkle them with dirt, say researchers, to increase the formation of ice spikes that shade large areas on the glaciers, slowing their melting.

Meredith Betterton of the University of Colorado at Boulder, US, and colleagues in France have been sprouting ice spikes in a lab freezer. They say the spikes mimic those found on mountain glaciers, notably above 4000 metres in the Andes. The real spikes can be up to 5 m high and are known as "penitentes" because they resemble precessions of white-hooded monks.

Betterton's replicas, however, are only a few centimetres high. She created them by putting blocks of snow in a freezer with a transparent lid and shining a spotlight onto them, mimicking sunlight. Within a few hours, sublimation of the snow had left spikes up to 5 centimetres high protruding from the surface (see image, top right).

When Charles Darwin first noticed penitentes while travelling through Chile, he noted that locals believed they were formed by strong winds. Betterton's lab experiments confirm what she had previously suggested after computer modelling: that sunlight forms the spikes independently of wind.

Localised melting

Initially, the Sun's rays cause random dimples on the surface of the snow. Once such a dimple is formed, sunlight can be reflected within the dimple, increasing the localised sublimation. As this accelerates, deep troughs are formed, leaving peaks of ice standing between them.

Next, the researchers tried sprinkling a thin layer of soot on fresh blocks of snow, to simulate the pollutants accumulating on some glaciers.

This made the penitentes form even faster. The soot had to be thin enough to let some light penetrate and kick off the formation of dimples in the snow. Once this happened, the troughs become lighter in colour as the soot layer was stretched across the dimples increased surface area. The soot acts as a sunscreen, protecting the peaks, meaning the dimples deepen even faster.

"The kick-off time went from 3 hours without a thin layer of dirt to 30 minutes with a thin layer of black powder from a photocopier," says Vance Bergeron of the Ecole Normale Supérieure in Lyon, France, one of Betterton's collaborators.

Chilled peaks

The formation of the penitentes ultimately slows the melting and preserves the remaining snow, for two reasons. Firstly, the towering peaks cast a shadow across the glacier. Secondly, the deep troughs create a larger surface for heat exchange, allowing gentle alpine winds to cool the surface of the glacier more efficiently.

"Theoretically, we also think that if the temperature gradient between the bottom of the troughs and the peaks is great enough, you could get evaporation in the troughs and re-condensation on the peaks," Bergeron told New Scientist.

Betterton is presenting these findings, published in Physical Review Letters in 2006 at a meeting of the American Physical Society in Denver, US, taking place from 5 to 9 March 2007.

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