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Sinkholes as big as a skyscraper and as wide as a city street open up in the Arctic seafloor

Giant "sinkholes" — one of which could devour an entire city block holding six-story buildings — are appearing along the Arctic se...

Giant "sinkholes" — one of which could devour an entire city block holding six-story buildings — are appearing along the Arctic seafloor, as submerged permafrost thaws and disturbs the area, scientists have discovered.

But even though human-caused climate change is increasing the average temperatures in the Arctic, the thawing permafrost that's creating these sinkholes seems to have a different culprit — heated, slowly moving groundwater systems. 

The Arctic permafrost at the bottom of the Canadian Beaufort Sea has been submerged for about 12,000 years, since the end of the last ice age, when meltwater from glaciers blanketed the region. Until now, the frozen seafloor had been hidden from scientists' peering eyes. This remote part of the Arctic has only recently become accessible to researchers on ships as climate change causes the sea ice to retreat, the researchers said. 

With access to the area, the study researchers relied on both ship-based sonar and an autonomous underwater vehicle (AUV) to complete high-resolution bathymetric surveys of the Canadian Beaufort Sea. 

"We know that big changes are happening across the Arctic landscape, but this is the first time we've been able to deploy technology to see that changes are happening offshore too," Charlie Paull, a geologist at Monterey Bay Aquarium Research Institute (MBARI), said in a statement. "While the underwater sinkholes we have discovered are the result of longer-term, glacial-interglacial climate cycles, we know the Arctic is warming faster than any region on Earth," added Paull, who co-led the research with Scott Dallimore from the Geological Survey of Canada and Natural Resources Canada, with an international team of researchers. 

When the researchers first started undertaking seafloor surveys in the region in 2010, they focused on the shelf edge and slope in the Canadian Beaufort Sea. About 110 miles (180 kilometers) from the shore, they spotted a 59-mile-long (95 km) band of unusually rough terrain along the seafloor. That stretch of seafloor once marked the edge of the Pleistocene permafrost during the last ice age. The team wondered what was causing the rugged nature of the ocean bottom.

To understand how this roughness evolved over time and what might be causing it, the team conducted three more surveys, using AUVs in 2013 and 2017 and then ship sonar in 2019. These snapshots of the same areas over time showed the emergence of steep-sided and irregularly shaped depressions. The largest sinkhole-like crater is a whopping 738 feet (225 meters) long, 312 feet (95 m) wide and 92 feet (28 m) deep, the researchers said. 

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