New study shows impact of Antarctic Ice Sheet on climate change

December 12, 2016

CORVALLIS, Ore. - Scientists have known for decades that small changes in climate can have significant impacts on the massive Antarctic Ice Sheet.

Now a new study suggests the opposite also is true. An international team of researchers has concluded that the Antarctic Ice Sheet actually plays a major role in regional and global climate variability - a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.

Results of the study are being published this week in the journal Nature.

Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a former post-doctoral researcher at Oregon State University now with the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

The research team's hypothesis was that climate modelers were overlooking one crucial element in the overall climate system - an aspect of the ocean, atmosphere, biosphere or ice sheets - that might affect all parts of the system.

"One thing we determined right off the bat was that virtually all of the climate models had the Antarctic Ice Sheet as a constant entity," Bakker said. "It was a static blob of ice, just sitting there. What we discovered, however, is that the ice sheet has undergone numerous pulses of variability that have had a cascading effect on the entire climate system."

The Antarctic Ice Sheet, in fact, has demonstrated dynamic behavior over the past 8,000 years, according to Andreas Schmittner, a climate scientist in Oregon State's College of Earth, Ocean, and Atmospheric Sciences and co-author on the study.

"There is a natural variability in the deeper part of the ocean adjacent to the Antarctic Ice Sheet - similar to the Pacific Decadal Oscillation, or El Niño/La Niña but on a time scale of centuries - that causes small but significant changes in temperatures," Schmittner said. "When the ocean temperatures warm, it causes more direct melting of the ice sheet below the surface, and it increases the number of icebergs that calve off the ice sheet."

Those two factors combine to provide an influx of fresh water into the Southern Ocean during these warm regimes, according to Peter Clark, a paleoclimatologist in OSU's College of Earth, Ocean, and Atmospheric Sciences and co-author on the study.

"The introduction of that cold, fresh water lessens the salinity and cools the surface temperatures, at the same time, stratifying the layers of water," Clark said. "The cold, fresh water freezes more easily, creating additional sea ice despite warmer temperatures that are down hundreds of meters below the surface."

The discovery may help explain why sea ice has expanded in the Southern Ocean despite global warming, the researchers say. The same phenomenon doesn't occur in the Northern Hemisphere with the Greenland Ice Sheet because it is more landlocked and not subject to the same current shifts that affect the Antarctic Ice Sheet.

"One message that comes out of this study is that the Antarctic Ice Sheet is very sensitive to small changes in ocean temperatures, and humans are making the Earth a lot warmer than it has been," Bakker said.

Sediment cores from the sea floor around Antarctica contain sand grains delivered there by icebergs calving off the ice sheet. The researchers analyzed sediments from the last 8,000 years, which showed evidence that many more icebergs calved off the ice sheet in some centuries than in others. Using sophisticated computer modeling, the researchers traced the variability in iceberg calving to small changes in ocean temperatures.

The Antarctic Ice Sheet covers an area of more than 5 million square miles and is estimated to hold some 60 percent of all the fresh water on Earth. The east part of the ice sheet rests on a major land mass, but in West Antarctica, the ice sheet rests on bedrock that extends into the ocean at depths of more than 2,500 meters, or more than 8,000 feet, making it vulnerable to disintegration.

Scientists estimate that if the entire Antarctic Ice Sheet were to melt, global sea levels would rise some 200 feet.
-end-
Other authors on the study include Nicholas Golledge of Victoria University of Wellington in New Zealand and Michael Weber of the University of Bonn in Germany.

Oregon State University

Related Ice Sheet Articles from Brightsurf:

Greenland ice sheet shows losses in 2019
The Greenland Ice Sheet recorded a new record loss of mass in 2019.

Warming Greenland ice sheet passes point of no return
Nearly 40 years of satellite data from Greenland shows that glaciers on the island have shrunk so much that even if global warming were to stop today, the ice sheet would continue shrinking.

Greenland ice sheet meltwater can flow in winter, too
Liquid meltwater can sometimes flow deep below the Greenland Ice Sheet in winter, not just in the summer, according to CIRES-led work published in the AGU journal Geophysical Research Letters today.

Ice sheet melting: Estimates still uncertain, experts warn
Estimates used by climate scientists to predict the rate at which the world's ice sheets will melt are still uncertain despite advancements in technology, new research shows.

Thousands of meltwater lakes mapped on the east Antarctic ice sheet
The number of meltwater lakes on the surface of the East Antarctic Ice Sheet is more significant than previously thought, according to new research.

Researchers discover ice is sliding toward edges off Greenland Ice Sheet
They found that ice slides over the bedrock much more than previous theories predicted of how ice on the Greenland Ice Sheet moves.

A clearer picture of global ice sheet mass
Fluctuations in the masses of the world's largest ice sheets carry important consequences for future sea level rise, but understanding the complicated interplay of atmospheric conditions, snowfall input and melting processes has never been easy to measure due to the sheer size and remoteness inherent to glacial landscapes.

Researchers discover more than 50 lakes beneath the Greenland Ice Sheet
Researchers have discovered 56 previously uncharted subglacial lakes beneath the Greenland Ice Sheet bringing the total known number of lakes to 60.

Ice-sheet variability during the last ice age from the perspective of marine sediment
By using marine sediment cores from Northwestern Australia, a Japanese team led by National Institute of Polar Research (NIPR) and the University of Tokyo revealed that the global ice sheet during the last ice age had changed in shorter time scale than previously thought.

Novel hypothesis goes underground to predict future of Greenland ice sheet
The Greenland ice sheet melted a little more easily in the past than it does today because of geological changes, and most of Greenland's ice can be saved from melting if warming is controlled, says a team of Penn State researchers.

Read More: Ice Sheet News and Ice Sheet Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.