Mapping the Arctic seafloor

Numerous peer-reviewed studies show that thawing permafrost creates unstable land, which negatively impacts important Arctic infrastructure, such as roads, train tracks, buildings, and airports. This infrastructure is expensive to repair, and the impacts and costs are expected to continue increasing. Thawing permafrost also impacts the Inuvialuit people and other Indigenous communities who live on the coast of the Beaufort Sea.

Using advanced underwater mapping technology, MBARI researchers and their collaborators revealed that dramatic changes are also happening to the seafloor due to thawing permafrost. In some areas, deep sinkholes have formed, some larger than a city block of six-story buildings. In other areas, ice-filled hills called pingos have risen from the seafloor.

This work is the first to document how the thawing of permafrost submerged underwater at the edge of the Arctic Ocean is affecting the seafloor.

MBARI’s autonomous mapping robots detailed the unusually rough seafloor terrain along the edge of the continental shelf in the Canadian Arctic. Sinkholes have developed where permafrost ice at depth has thawed, forming voids into which the seafloor collapsed. The circular mounds formed where the brackish water produced from the relict permafrost decay has migrated upwards and frozen, blistering the seafloor with ice-cored mounds called pingos. Image: Eve Lundsten © 2022 MBARI

While 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 has documented on the seafloor associated with submarine permafrost derive from much older, slower climatic shifts related to our emergence from the last ice age. Similar changes appear to have been happening along the seaward edge of the former permafrost for thousands of years.

While the underwater sinkholes the team discovered are the result of longer-term, glacial-interglacial climate cycles, the Arctic is warming faster than any region on Earth. As climate change continues to reshape the Arctic, it is critical that scientists also understand changes in the submerged permafrost offshore.

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 can conduct detailed surveys and assess changes in the seafloor.

These 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.

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 Korea Polar Research Institute. Support for this work was provided by the David and Lucile Packard Foundation, the Geological Survey of Canada, Fisheries and Oceans Canada, and the Korean Ministry of Ocean and Fisheries (KIMST grant No. 1525011795).

Repeated seafloor mapping 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 the 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.

“As climate change continues to reshape the Arctic, it’s critical that we also understand changes in the submerged permafrost offshore.” —MBARI Senior Scientist Charlie Paull

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 from 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.

Repeated surveys with MBARI’s mapping AUVs revealed dramatic and rapid changes to seafloor bathymetry from the Arctic shelf edge in the Canadian Beaufort Sea. This massive sinkhole developed in just nine years. Image: Eve Lundsten © 2022 MBARI

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.

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 this 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 terrestrial landforms, 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. 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 important in sculpting the seafloor throughout the Arctic.

The research team returned to the Arctic last summer aboard the R/V Araon, a Korean icebreaker. This trip with MBARI’s long-time Canadian and Korean collaborators gathered new data to help refine our understanding of the decay of submarine permafrost.

A team of 11 scientists and engineers from MBARI boarded the Araon in Utqiagvik, Alaska (formerly Barrow), along with other researchers from Korea, Canada, and the United States. From Utqiagvik, the Araon transited east, passing along the entire north shore of Alaska before entering into the study areas in Canadian waters.

In addition to KOPRI and MBARI, several other groups are present—the Geological Survey of Canada (GSC), the Naval Research Laboratory (NRL), Gwangju Institute of Science and Technology (GIST), Pohang University of Science and Technology (POSTEC), a representative of the Korean Navy, a marine mammal observer, and even an artist who will be making a documentary about the expedition.

The MBARI team brought two AUVs to continue repeated mapping surveys of the seafloor. When conducted at repeated intervals, the surveys reveal how dynamic areas like these change over time.

MBARI’s MiniROV also helped the research team explore and sample the freshly altered seafloor. This remotely operated vehicle was designed to be small and robust so that it could be easily shipped to remote ports, providing access to study areas beyond the west coast of North America. The MiniROV utilizes an articulated arm to collect water samples, sediment samples, and animals, while recordings from a high-resolution video camera provide insight about the precise context of their locations.

Repeated expeditions to the Canadian Beaufort Sea have helped MBARI and our collaborators continue to investigate the effects of thawing submarine permafrost. Because almost nothing is known about the decomposition of relict permafrost under the sea, the information gathered on each expedition will provide foundational insights into how and why this part of the world is changing.

This marine geoscience research program takes place in the Inuvialuit Settlement Region. The research program was reviewed by Inuvialuit Environmental Impact Screening Committee (EISC Registry File: 01-22-08), the Government of Northwest Territories (License No. 16995), the Government of Yukon (License No. 22-11S&E), and the Department of Foreign Affairs, Trade and Development Canada (Permit – IGR-1283).

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 expanding human presence is especially important and urgent. This ongoing research in the Arctic exemplifies MBARI’s mission to advance ocean science and technology to understand a changing ocean.

Eavesdropping on the largest animal on Earth

Researchers use acoustic data to reveal the secretive lives of blue whales.