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Researchers uncover dynamic processes that shape the Arctic seafloor

Repeated surveys by MBARI’s ocean floor mapping autonomous underwater vehicle have revealed unique landforms, including the rapid formation of giant craters and large mounds, on the edge of Canada’s Beaufort Sea continental shelf. Credit: : Eve Lundsten, MBARI

MBARI researchers, working with a team of international collaborators, have discovered a large underwater ice formation at the edge of Canada’s Beaufort Sea, located in a remote part of the Arctic Circle. This discovery reveals an unexpected mechanism for the ongoing formation of submarine permafrost ice. The discovery is published in the Journal of Geophysical Research: Earth Surface.

In MBARI’s previous study, researchers observed giant craters on the ocean floor in the area, which are believed to be caused by thawing ancient permafrost that was submerged underwater.

MBARI researchers and collaborators from the Korea Polar Research Institute (KOPRI), the Korea Institute of Geology and Mineral Resources, the Geological Survey of Canada, and the U.S. Naval Research Laboratory have explored the sides of these craters in subsequent expeditions, uncovering the exposed geological formations. observed. Undersea permafrost ice.

The recently discovered ice layer is not the same as the ancient permafrost that formed during the last ice age, but rather formed under modern conditions. This ice is created when deeper layers of ancient submarine permafrost melt, producing brackish groundwater that rises and refreezes as it approaches the ocean floor, where ambient temperatures are about -1.4 degrees Celsius (29.5 degrees Fahrenheit). Masu.

Credit: Monterey Bay Aquarium Research Institute

The complex morphology of the ocean floor in this region of the Arctic tells a story that involves both the thaw of ancient permafrost that sank beneath the ocean in ancient times, and the modern deformation of the ocean floor that occurs as released water refreezes. It tells the story.

After the last ice age, sea levels rose and covered the ancient permafrost of the Arctic shelf. The base of this ancient permafrost is slowly warming and thawing due to heat escaping from the earth. This thawing of permafrost on the Arctic ocean floor is not due to human-induced climate change, but to much older, slower-paced climate change.

When this water moves to the cold ocean floor, it freezes. When ice freezes, it pushes up ridges and hills. Seawater seeps into the swollen ocean floor surface, melting the ice layer and leaving huge sinkholes. The dynamic interaction between large changes in salinity and small changes in temperature near the ocean floor drives this process.

MBARI geologist and lead author Charlie Paul said: “Our study shows that permafrost ice is actively forming and breaking down over large areas near the ocean floor, creating large sinkholes and deposits. “This shows that there are large ice-covered mountains creating a dynamic underwater landscape.” of research.

“These dramatic and ongoing seafloor changes have major implications for policymakers making decisions about Arctic underwater infrastructure.”

New MBARI study reveals dynamic processes shaping the Arctic ocean floor

An international research team led by MBARI Senior Scientist Charlie Paul used MBARI’s advanced underwater technology to document the dynamic processes that carve the ocean floor in a remote part of the Arctic Ocean. A team of researchers has discovered a large underwater ice formation in Canada’s Beaufort Sea. This discovery reveals an unexpected mechanism for the ongoing formation of submarine permafrost ice. Credit: Dave Caress 2022 MBARI

Since 2003, MBARI has participated in an international collaboration to study the ocean floor at the edge of Canada’s Arctic shelf. Scientists have only recently gained access to this remote area as rising temperatures have caused sea ice to retreat.

A 2010 mapping study by Canadian researchers first revealed the area’s characteristically rugged underwater topography. In 2013, MBARI researchers and their collaborators conducted the first high-resolution mapping survey of the region. The research team used the MBARI autonomous underwater vehicle (AUV) to record the topography of the ocean floor in detail.

Five mapping surveys conducted in the area over 12 years (two carried out by Canadian research vessels and three using MBARI’s advanced underwater technology) revealed new formations on the ocean floor. 65 craters were revealed. The largest crater was the size of a city block lined with six-story buildings.

In 2022, the team returned to the Arctic aboard KOPRI’s icebreaker research vessel Araon. They first used MBARI’s two ocean floor mapping AUVs to identify recently formed craters. A visual survey was then conducted within the specific crater using MBARI’s MiniROV. Developed by MBARI engineers, this portable remotely operated vehicle can be configured for a variety of scientific missions.

It is equipped with cameras and sampling equipment, making it essential for studying the Arctic seafloor. While exploring the ocean floor with a MiniROV, researchers observed ice formation inside two large, recently formed underwater craters.

Isotope analysis of samples of these formations and surrounding seafloor sediments confirms that the ice originates from brackish groundwater and is partly formed by melting ancient permafrost that rose from the ocean floor. It was done. The rising groundwater refreezes near the ocean floor, forming an extensive subseafloor ice layer that swells the ocean floor, forming ice blocks.

Small changes in temperature and salinity cause shifts between freezing of rising brackish groundwater and melting of ice layers near the ocean floor. These continuous processes work together to create a dramatic underwater landscape consisting of numerous depressions and ice-filled hills of varying ages.

“These findings challenge our assumptions about underwater permafrost,” Paul said. “We previously believed that all underwater permafrost was left over from the last Ice Age, but now we know that underwater permafrost ice is actively forming and breaking down even on the modern ocean floor. ”

This process of forming sub-seafloor ice layers has not been considered before and can occur where ocean-bottom water temperatures are below 0 degrees Celsius.

“This discovery means that the techniques we have previously used to locate submarine permafrost will not work for the type of near-seafloor ice we recently discovered exists in the Arctic. . We now need to reconsider where permafrost may exist beneath the Arctic shelf,” Paul said.

Further information: Charles K. Paull et al., “Massive ice outcrops and thermokarst along the Arctic shelf edge: a byproduct of ongoing groundwater freezing and thawing,” Journal of Geophysical Research: Earth Surface (2024) . DOI: 10.1029/2024JF007719

Provided by: Monterey Bay Aquarium Research Institute

Citation: Researchers reveal dynamic process sculpting arctic seafloor (October 8, 2024) https://phys.org/news/2024-10-reveal-dynamic-sculpt-arctic-seafloor.html Retrieved October 8, 2024 from

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