9 December 2011

Really cool but depressing science

Posted by kramsayer

Aerial view of permafrost polygons--each measuring about 30 feet across-- at Axel Hieberg Island in Northern Canada. (Credit: Timothy Haltigin)

The Arctic permafrost is a landscape of geometric wonder. Honeycombs of polygonal depressions are common in these far northern regions of Earth, echoing some observed on Mars. Scientists want to know what clues these depressions could provide about our own planet and how similar features could have formed on Mars.

To help reconstruct landscape history, scientists rolled ground-penetrating radar along the frozen Earth in the high Arctic. This produced the clearest imagery available of ice wedge patterns, which sit below the surface of the polygon troughs. These upside-down triangles of ice rest just below a layer of porous frozen sediment, which thaws and freezes each year.

The boundary between the wedges and the frozen sediment intrigues researchers, who attribute the changes along that boundary to recent observations of a slumping permafrost. Tim Haltigin of the Canadian Space Agency presented a poster showing his team’s findings Thursday morning at the American Geophysical Union’s Fall Meeting.

The freezing and thawing surface layer they studied might deepen during extended warming or higher temperatures and consequently melt the top of the ice wedge, shrinking it, Haltigin said. If the top layer thins in following years, it will no longer sit on a solid base of ice. In these conditions, the ground could collapse under its own weight, forming a depression.

Because of this process, the surface cracking now found across many areas of the permafrost landscape could act as a red flag for a warming climate, Haltigin said.

The research team hand-drilled on both sides of these slumping cracks and found that the ice wedge width lined up neatly beneath the subsiding ground. Because ground-penetrating radar accurately measured the outlines of the wedges, the team was encouraged to continue using this high-resolution technology.

An earlier study compared the geometry of Earth’s permafrost patterns to those on Mars. Though climatic similarities exist between present day Mars and Earth’s polar regions, Haltigin, a planetary scientist, states confidently that these “ice wedges are almost absolutely not on Mars,” because of a lack of liquid water on its surface. Instead, Haltigin said, wedges of frozen porous sediment  may be causing the Martian troughs.

“What gets me up in the morning,” Haltigin said, “is trying to understand the evolution of frozen landscapes on Earth and Mars.”

-Amy West is a science communication graduate student at UC Santa Cruz