"Ice Arches" Act as Gatekeepers to Melting Arctic Ice

It's easy to imagine the Arctic ice cap as it looks on a globe -- pinned firmly to one spot. However, that's not the case. Sea ice is free to roam when it breaks up, bobbing out of the Arctic Ocean through straits that head toward the Atlantic and Pacific. Normally, natural ice dams, or "ice arches," block these straits, hemming in wandering ice. They cut off major openings like the Bering Strait and plug holes throughout the Canadian archipelago. But with some of the arches now failing to form, ice is leaving the Arctic at a record rate.

Ronald Kwok of the Jet Propulsion Laboratory studied one exit point in particular: the Nares Strait, a slim passage that cuts between Canada's Ellesmere Island and Greenland. Kwok's team used satellite images from 1997 to 2009 to track the annual ice flow out of the Arctic via the Nares Strait. Usually, "ice arches" formed in mid- to late-winter to block the escaping flow. They'd last until early summer when the exiting ice would eventually breach the weakening dams. But in 2007, one of the warmest Arctic years on record, the arches never formed at all. Consequently, more than twice the amount of ice that normally passed through the strait escaped the Arctic, and sea ice extent reached a record low.

The unblocked strait also proved to be an especially high-volume route to the open ocean, despite its narrowness. The 2007 flow through the 24-mile-wide (40-kilometer-wide) Nares equaled nearly 10 percent of what flowed through the Fram Strait, an expanse of water between Greenland and Svalbard too wide to even form "ice arches." According to the Jet Propulsion Laboratory, 34,000 square miles (88,060 square kilometers) of ice left through the Nares Strait -- ice the organization calls some of the "thickest and oldest in the Arctic Ocean."

With "ice arches" playing such an obviously important role in maintaining the Arctic cap, the loss of a key dam, even if only for a year, could result in some problems. The 2007 ice loss will likely take time to make up, potentially resulting in lighter summer coverage for years. And since, according to ScienceDaily, the arches themselves are formed by exiting blocks that get clogged in the strait, a smaller ice flux combined with warmer temperatures could cause the arches to stop forming at all. 

Images: Top, In this satellite image taken on Dec. 23, 2007, ice can be seen heading toward the Nares Strait. (Photo courtesy the European Space Agency) Middle, figures depicting record low sea ice coverage at the end of the 2007 melt season.