Scientists have reconstructed 30,000 years of changes to sea ice in several locations across the Arctic Ocean by looking for traces of cosmic dust embedded in the seafloor, according to a study published Thursday.
Scientists analyzed sediment samples from the Arctic Ocean by looking for traces of space particles, which fall through the atmosphere at a constant rate and blanket exposed surfaces. If those particles reached the ocean floor, it’s an indication that there was no sea ice blocking their path during the years that a particular sediment layer formed.
“The Earth has undergone major climate shifts over the past 30,000 years,” said Frankie Pavia, an assistant professor of oceanography at the University of Washington and the lead author of the study, which was published in the journal Science. “That gives us a place where we can go look and say: ‘Hey, this is probably where we’re headed. It might even be where we are now.’”
The new study’s analysis represents the first step toward better understanding how the Arctic responded to different conditions before satellites started measuring ice coverage about 50 years ago.
Large sheets of frozen sea ice float on the Arctic and Antarctic oceans, melting and refreezing seasonally, with the amount of ice typically peaking at the end of winter. This year, Arctic sea ice failed to recover as much as usual, and a record-low maximum was recorded in March, according to the National Snow and Ice Data Center at the University of Colorado Boulder.
Over the last half century, the overall amount of sea ice has been declining. The ice that survives year-round is thinner and more fragile than before, and only 5 percent of the oldest and thickest sea ice remains.
The Arctic is rapidly transforming as human activity adds greenhouse gases to the atmosphere and global temperatures rise. This year is on track to be the second or third warmest in recorded history, according to the World Meteorological Organization.
Sea ice helps reflect the sun’s heat back into space, and less of it means that more dark, heat-absorbing ocean is exposed; it is one factor in a feedback loop that is causing the Arctic to warm nearly four times as fast as the rest of the planet.
The ice also provides a habitat for marine wildlife like polar bears and seals. Arctic Indigenous communities have been forced to adapt their hunting and fishing practices as the ice melts. Less ice also means the Arctic Ocean is more passable, opening up new shipping routes and raising new questions for national security.
Cosmic dust is a fine debris created by activity in space, like the collision of asteroids or comets, and carries a particular helium isotope signature that can be detected by lab analysis.
The researchers of the new study looked for this helium signature in sediment cores and found that hardly any cosmic dust reached the ocean floor during the last ice age, indicating that there was a constant layer of sea ice. Over millenia, as the climate gradually warmed up to the preindustrial temperatures, more of these particles accumulated in the seabed. Each centimeter of sediment represents about 1,000 years of buildup.
The researchers also tested for another a thorium isotope, which helped confirm that the changes in detectable helium were indeed because of sea ice and not other environmental factors.
Seeing their initial results “really set us off to the races of saying, I think we really have a way we can study past ice changes in the Arctic,” Dr. Pavia said.
Walter Geibert, a marine geochemist at the Alfred Wegener Institute in Germany who was not involved with the study, said using cosmic dust to study sea ice was an exciting and scientifically necessary step forward. “It really adds a new tool to our understanding of the Arctic Ocean, which is one of the least understood regions globally,” he said.
Existing techniques for reconstructing past sea ice primarily use the remains of microorganisms that typically live at the edge of ice masses and are not as robust nor as reliable as the method demonstrated by the new study, he said.
Dr. Pavia hopes cosmic dust can be used to answer key unanswered questions about Earth’s past and future.
But to do that, researchers will need more samples, which can be difficult and costly to get. Dr. Pavia’s study used sediment cores from three locations, collected in 1994 during the United States’ first major scientific expedition to reach the North Pole and have been held in storage ever since.
Now that scientists can begin tackling sea ice comprehensively, other parts of the puzzle can be filled in, Dr. Geibert said. “It’s like a big equation with many unknowns, and now you can tackle more of them.”
Sachi Kitajima Mulkey covers climate and the environment for The Times.
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