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Arctic mapping redraws borders

Secrets emerge from 'least-mapped place in the world'.

The Chukchi Cap, shown under the yellow highlight of the research area, is now known to be 100 miles longer. Credit: NOAA

The recent push for nations to stake a claim to portions of the Arctic sea floor, where potential oil reserves are thought to lie, has thrown a spotlight on how little is known about these areas, and on new attempts to pin the geography down.

Earlier this week, the United States announced that their survey of the sea floor of the Chukchi Cap, a giant underwater peninsula north of Alaska (see map), showed that the foot of its continental slope — where the continental shelf falls off into the ocean basin — is more than 100 nautical miles farther from the US coast than was previously believed.

Under the United Nations Convention on the Law of the Sea (UNCLOS), nations can submit a claim to the sea floor off their coasts if they can prove certain geological criteria (see 'Law of the Sea'). Although the United States has yet to ratify the Convention, it is expected that the data will go towards a future claim on these areas.

Meanwhile, Canadian expeditions are likewise underway. "Unlike the Americans, we're not going to comment on where we have found our boundary until we have put together the scientific evidence to make the case," says Jacob Verhoef, director of the Atlantic division of the Geological Survey of Canada.

Verhoef told Nature News that a Canadian expedition in the Beaufort Sea last year found a surprising amount of sediment — another one of the geological criteria by which nations can lay claim to sea floor — which resulted in their survey area being expanded. If the survey had to extend its coverage this would imply that the possible claim is larger than it was originally thought to be.

Map-making

"This is the least mapped place in the world," says Larry Mayer, chief scientist on the recent US expedition and director of the Center for Coastal and Ocean Mapping at the University of New Hampshire in Durham. "It's taken this new interest in the Arctic to get us to bring an ice-breaker with a very fancy mapping system."

The fact that the Arctic is covered in ice for much of the year makes gathering data on the sea floor problematic. Enough ice persists in the summer to make an ice-breaker necessary. "It's a very challenging, and therefore expensive, area to collect that data from," says Lindsay Parson, a UNCLOS expert at the University of Southampton, UK. So it isn't surprising, he says, that the extent of the Arctic continental shelf remains unclear.

Last summer, there was an unprecedented retreat of sea ice (see 'Arctic sea ice at record low'). While "sad for the Arctic", says Mayer, this was a boon for his expedition. If future years continue to have such little ice, it will make the map-making easier.

Ping

Historically, Arctic seafloor data came from cutting a hole in the ice and lowering an echo sounder, or from rather inaccurate and sparse submarine readings.

"The amount of data we have in the arctic is woefully inadequate," says Verhoef. "In many areas there are 30 or 40 kilometres between data points." And these data points can in themselves be inaccurate: old echo-sound data were arrived at by sending a ping of sound into the sea. In an area with a depth of 3,000 metres, the resulting signal could come from anywhere within a 3,000-metre-wide circle, says Mayer.

Some modern surveys, including the recent US expedition, use multibeam sonar, which projects a fan of sound and uses computer software to integrate the result into a more accurate map. "You can't get better than that," says Parson.

"With respect to how much of the ocean has been mapped by these techniques, it's a very small percentage," says Mayer. "Maybe 5 to 10% of the ocean is mapped at that level of detail."

Still the least-mapped area remains the Arctic, where there are probably further discoveries to be made that will redraw the map.

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Cressey, D. Arctic mapping redraws borders. Nature (2008). https://doi.org/10.1038/news.2008.603

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