Across the Arctic, numerous peer-reviewed studies show that thawing permafrost creates unstable land which negatively impacts important infrastructure and impacts Indigenous communities. Now, a new study from MBARI researchers and their collaborators published in the Proceedings of the National Academy of Sciences finds dramatic changes offshore and is the first to document how the thawing of permafrost submerged underwater at the edge of the Arctic Ocean is affecting the seafloor.

About one quarter of the land in the Northern Hemisphere is permafrost or frozen ground. At the end of the last ice age (12,000 years ago) melting glaciers and sea level rise submerged large swaths of permafrost. Until just recently, this submerged permafrost had been largely inaccessible to researchers. But now, thanks to technological advancements, including MBARI’s autonomous mapping robots, scientists are able to conduct detailed surveys and assess changes in the seafloor.

High-resolution bathymetric surveys in the Canadian Beaufort Sea have revealed changes in the seabed from 2010 to 2019. Using autonomous mapping robots, scientists documented multiple large sinkhole-like depressions—the largest the size of an entire city block of six-story buildings—had developed in less than a decade. 

“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,” said Charlie Paull, a geologist at MBARI who led the study with Scott Dallimore from the Geological Survey of Canada, Natural Resources Canada, and an international team of researchers. “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. As climate change continues to reshape the Arctic, it’s critical that we also understand changes in the submerged permafrost offshore.”

Since 2003, MBARI has been part of an international collaboration to study the seafloor of the Canadian Beaufort Sea with the Geological Survey of Canada, the Department of Fisheries and Oceans Canada, and since 2013, with the Korean Polar Research Institute. Support for this work was provided by the David and Lucile Packard Foundation, Geological Survey of Canada, Fisheries and Oceans Canada, and the Korean Ministry of Ocean and Fisheries (KIMST grant No. 1525011795).

“This research was made possible through international collaboration over the past decade that has provided access to modern marine research platforms such as MBARI’s autonomous robotic technology and icebreakers operated by the Canadian Coast Guard and the Korean Polar Research Institute,” said Dallimore. “The Government of Canada and the Inuvialuit people who live on the coast of the Beaufort Sea highly value this research as the complex processes described have implications for the assessment of geohazards, creation of unique marine habitat, and our understanding of biogeochemical processes.”

Repeated mapping of the seafloor with ship-based sonar and an autonomous underwater vehicle (AUV) were critical to this work. MBARI’s mapping AUVs can resolve the bathymetry of the seafloor down to a resolution of a one-meter (about three-feet) square grid, or roughly the size of a dinner table. These self-guided robots have been instrumental in enabling detailed visualization of the seafloor and documenting changes over time.

In 2010, while conducting the first systematic multibeam mapping surveys of part of the shelf edge and slope in the Canadian Beaufort Sea, researchers found a band of unusually rough seafloor terrain along a 95-kilometer (59-mile) stretch of the shelf roughly 180 kilometers (110 miles) offshore, along what was once the seaward limit of relict Pleistocene permafrost. Repeated surveys allowed researchers to begin to understand the processes creating the distinctively rugged seafloor terrain in the Canadian Beaufort Sea.

The three subsequent multibeam surveys—with AUVs in 2013 and 2017 and by ship in 2019— provided high-resolution maps of a smaller area of 4.8 square kilometers (1.9 square miles) near the edge of submerged permafrost 120 to 150 meters (394 to 492 feet) deep to help researchers understand the processes responsible for the unique seafloor features first observed in 2010. The differences measured in these surveys over a nine-year period provided three snapshots of rapid and dynamic changes in seafloor morphology. 

Researchers documented the formation of new, irregularly shaped, steep-sided depressions. The largest was an oval-shaped depression 28 meters (92 feet) deep, 225 meters (738 feet) long, and 95 meters (312 feet) wide. The research team attributes these changes to intermittent seafloor collapse due to the gradual warming of the permafrost sediment frozen beneath the Arctic Shelf since the end of the last ice age. 

The degradation of terrestrial Arctic permafrost is attributed, in part, to increases in mean annual temperature from human-driven climate change. The changes the research team documented derive from much older, slower climatic shifts related to our emergence from the last ice age, and similar changes appear to have been happening along the seaward edge of the former permafrost for thousands of years.

“We don’t have a lot of long-term data for the seafloor temperature in the Canadian Beaufort Sea, but the available data do not show a warming trend, which ruled out anthropogenic climate change driving the dramatic changes in the seafloor terrain. Instead, heat carried in slowly moving groundwater systems is driving these changes,” explained Paull.

Brackish groundwater generated from the thawed permafrost percolates upwards along the bottom edge of the remaining relict permafrost bodies, accelerating the thawing of the permafrost in the sediments above. Water-filled cavities replace the excess ice that was once within the relict permafrost. Previously permafrost-filled subsurface voids periodically collapsed to produce the large and rapidly formed sinkholes observed on the seafloor. 

The research team also documented other distinct seafloor features created by water from thawing permafrost.

In areas where groundwater discharge is more limited, the bottom ocean waters keep the near-seafloor sediment temperature low enough for the ascending brackish waters to refreeze as they approach the slightly colder seafloor. When ice in near-seafloor sediments freezes, it expands, creating pingos—circular hills with a core of ice. The maps of the seafloor revealed an abundance of pingos adjacent to the main discharge area. While pingos were previously viewed primarily as a terrestrial landform, this study has confirmed these features are in fact submarine pingos. The density of these pingos is the highest known anywhere.

“The ongoing melting of relict permafrost under the Arctic Shelf, expulsion of brackish waters, and the formation of new ground ice within the near seafloor sediments work in concert to create the unique and rapidly changing morphology observed on the Arctic seabed,” said Paull. “These rapid changes to the seafloor demand our attention. We need to understand how the decay of relict submarine permafrost will impact the vast areas underlying the Arctic continental shelves. This groundbreaking research has revealed how the thawing of submarine permafrost can be detected, and then monitored once baselines are established.”

The team expects that similar processes may also be occurring in other submarine permafrost systems. How widespread similar changes are on the Arctic shelves remains unknown, as this is one of the first areas in the Arctic studied with multiple multibeam bathymetric surveys. However, permafrost thawing may be an important process in sculpturing the seafloor throughout the Arctic.

The research team will return to the Arctic this summer aboard the R/V Araon, a Korean icebreaker. This trip with MBARI’s long-time Canadian and Korean collaborators—along with the addition of the United States Naval Research Laboratory—will help refine our understanding of the decay of submarine permafrost.

Two of MBARI’s AUVs will map the seafloor in remarkable detail and MBARI’s MiniROV—a portable remotely operated vehicle—will enable further exploration and sampling to complement the mapping surveys.

The Canadian Beaufort Sea, a remote area of the Arctic, has only recently become accessible as climate change drives the retreat of sea ice. Learning about the fragile Arctic environment before it becomes further altered by the expanding human presence is especially important and urgent. This ongoing research in the Arctic and the upcoming expedition exemplify MBARI’s mission to advance ocean science and technology to understand a changing ocean.

Research Publication:
Paull, C.K., S.R. Dallimore, Y.K. Jin, D.W. Caress, E. Lundsten, R. Gwiazda, K. Anderson, J.H. Clarke, S. Youngblut, and H. Melling (2022). Rapid seafloor changes associated with the degradation of Arctic submarine permafrost. Proceedings of the National Academy of Sciences, 119: e2119105119. doi.org/10.1073/pnas.2119105119 

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