A new study from Oregon State University suggests that tiny air bubbles may be ramping up the rate of glacier melt, ultimately contributing to sea level rise.
The research suggests that the rapid retreat of tidewater glaciers – glaciers that terminate at the sea – may be influenced by the bursting of pressurized air bubbles trapped in the ice.
In the journal Nature Geoscience, the experts describe the melting behavior of glacier ice compared to other forms of ice. Unlike the bubble-free sea ice or manufactured ice typically used in research, glacier ice undergoes melting at a much faster rate.
This revelation carries significant implications, especially considering that tidewater glaciers around the world, from Greenland to the Antarctic Peninsula, are retreating at unprecedented speeds.
“We have known for a while that glacier ice is full of bubbles,” said study lead author Meagan Wengrove, assistant professor of Coastal Engineering at OSU. “It was only when we started talking about the physics of the process that we realized those bubbles may be doing a lot more than just making noise underwater as the ice melts.”
But what is the origin of these bubbles? As snow compacts to form glacier ice, the air pockets nestled between snowflakes find themselves trapped within the ice’s pores.
With an estimated 200 bubbles per cubic centimeter, glacier ice consists of approximately 10% air.
“These are the same bubbles that preserve ancient air studied in ice cores,” said study co-author and glaciologist Erin Pettit. “The tiny bubbles can have very high pressures – sometimes up to 20 atmospheres, or 20 times normal atmospheric pressure at sea level.”
As the bubbly glacier ice reaches the sea, these pressurized bubbles rupture, creating distinct popping sounds. Despite the prior knowledge of these bubbles’ existence, Wengrove noted the absence of studies investigating their impact on melting at the glacier-ocean interface.
“The existence of pressurized bubbles in glacier ice has been known for a long time but no studies had looked at their effect on melting where a glacier meets the ocean, even though bubbles are known to affect fluid mixing in multiple processes ranging from industrial to medical,” said Wengrove.
Lab experiments indicate that these bubbles might be a piece of the puzzle, bridging the gap between observed and anticipated melt rates of tidewater glaciers.
“The explosive bursts of those bubbles, and their buoyancy, energize the ocean boundary layer during melting,” explained Wengrove.
This discovery could radically reshape climate models, particularly those focusing on the topmost 40 to 60 meters of the ocean. The team found that glacier ice laden with bubbles melts more than twice as rapidly as bubble-free ice.
Pettit emphasized the challenge posed by existing models. “The models currently used to predict ice melt at the ice-ocean interface of tidewater glaciers do not account for bubbles in glacier ice.”
Such findings have profound implications for predicting global sea-level rise. At present, NASA data attributes roughly 60% of sea level rise to meltwater from glaciers and ice sheets.
Achieving a more precise understanding of ice melt mechanisms can enhance predictions of glacier retreat rates. Wengrove highlighted the practical implications of these findings, noting, “it’s a lot more difficult for a community to plan for a 10-foot increase in water level than it is for a 1-foot increase.”
Wengrove also emphasized the broader significance of these tiny bubbles. “Those little bubbles may play an outsized role in understanding critical future climate scenarios.”
The research was funded by the Keck Foundation, the National Science Foundation, and the National Geographic Society.
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