Research from Oregon State University has discovered a potential reason for the rapid retreat of ocean-end glaciers: the collapse of tiny pressurized bubbles in the underwater ice. Recent research published in the journal Nature Geoscience shows that glacier ice is filled with pressurized bubbles and melts significantly faster than sea ice without bubbles, and faster than artificial ice commonly used to study the melting rate of sea-ice interfaces in tidewater glaciers.
New research finds that the collapse of tiny pressurized bubbles in underwater glacier ice may explain why tidewater glaciers are retreating at an alarming rate. The study found that such bubble-filled glaciers melted at more than twice the rate of bubble-free glaciers, suggesting the need to adjust climate models that currently do not account for these bubbles.
Tidewater glaciers are retreating rapidly, causing ice loss in Greenland, the Antarctic Peninsula and other glaciated regions around the world, the authors say.
"We've known for a long time that glacial ice is full of air bubbles," said Meagan Wengrove, assistant professor of coastal engineering in the OSU College of Engineering and leader of the study. "Only when we started discussing the physics of this process did we realize that these bubbles might be doing more than just making noise underwater as the ice melts."
Glacier ice is the result of snow compaction. As the ice travels from the upper levels of the glacier to the depths of the glacier, air bubbles between the snowflakes become trapped in the pores between the ice crystals. There are about 200 air bubbles per cubic centimeter, which means that about 10 percent of the glacier ice is air.
"These bubbles are the same ones that preserve the ancient air studied in ice cores," said co-author Erin Pettit, a glaciologist and professor in OSU's School of Earth, Ocean and Atmospheric Sciences. "The pressure of these tiny bubbles is very high, sometimes reaching 20 atmospheres, which is 20 times the normal atmospheric pressure at sea level."
She added that when the bubble ice reaches the interface with the ocean, the bubbles burst, making a "pop" sound. The existence of pressurized air bubbles in glacier ice has long been known, but no study has examined the effects of air bubbles on melting where glaciers meet the ocean, even though air bubbles are known to affect fluid mixing in processes ranging from industrial to medical.
Laboratory-scale experiments conducted in this study suggest that bubbles can explain some of the discrepancy between observed and predicted melt rates for tidewater glaciers, Wengrove said: "During the melting process, the bursting of these bubbles and their buoyancy injects energy into the ocean boundary layer."
Researchers learned that glaciers melted at more than twice the rate of glaciers without air bubbles.
"While we can measure Greenland's overall ice loss over the past decade and see the retreat of each glacier from satellite images, we still rely on models to predict how fast the ice is melting," Pettit said. "Current models used to predict ice melt at the ice-ocean interface of tidal glaciers do not take into account air bubbles in the glacier ice."
The authors point out that currently, data provided by the National Aeronautics and Space Administration (NASA) shows that about 60% of sea level rise is attributed to meltwater from glaciers and ice sheets. "It's much harder for a community to plan for a 10-foot rise in water levels than it is to plan for a one-foot rise," Wengrove said. "These little bubbles could play a huge role in understanding key climate scenarios in the future."