Ice core samples are a great way to analyze historic climate changes. The ice often contains impurities, such as sulfuric acid or sea salt, that give some indication of the conditions under which they were frozen in time. But researchers at the University of Washington have found that these impurities can travel through the ice between individual crystals by way of microscopic channels filled with liquid water. And they travel far enough to muddy the results of some core analyses. The study, which examined ice cores taken from Greenland and Antarctica, appears in today's Nature.

"The ice cores themselves are wonderful records of climate. Nobody is questioning that," Alan Rempel says. But the impurities are unreliable. Over time these substances sink into the iceand the deeper they go, the warmer it gets and the faster they sink. Thus after thousands of years substances buried three kilometers deep can be more than 50 centimeters away from their original location. "The point of the paper is to suggest that the ice core community go back and redo the chemistry," John Wettlaufer says. The researchers hope to design a model that will help scientists predict how much impurities have moved in ice samples and adjust their results accordingly.