With ice balls, lasers, and cameras, School of Arts & Sciences’ Hugo Ulloa recreated a melting iceberg in his lab. This project revealed that icebergs don’t sit passively on the water’s surface but actually release dense, cold water and jet across the surface, churning and mixing everything in their paths.
2 min. read
A melting ice cube in lemonade will quickly water down a drink—disappointing, but not dire. It’s different in the ocean when even the smallest of icebergs melts faster than expected. That, says geophysicist Hugo Ulloa, can have serious consequences.
Research from Hugo Ulloa, an assistant professor in the Department of Earth & Environmental Science, and Daisuke Noto of Hokkaido University, models how icebergs melt and move in their environments.
(Image: Gabi Musat / 500px via Getty Images)
As the Earth warms up, the massive ice sheets covering its poles are breaking off more icebergs than ever before in our current era. Many end up in the ocean, but smaller ones—sometimes called “bergy bits” or “growlers”—often calve into coastal areas, like the fjords of Greenland and Alaska, where water temperatures reach a relatively balmy 50° Fahrenheit in the summer.
Though these smaller icebergs are especially hard to track, according to Ulloa, an assistant professor in the Department of Earth & Environmental Science in the School of Arts & Sciences, that doesn’t mean they’re not affecting their environments in ways that climate, ocean, and weather models should take into account.
For that reason, Ulloa and Daisuke Noto—an assistant professor at Hokkaido University in Japan who recently completed his postdoc at Penn—set out to model the ways small icebergs melt and move in their environments. They used lasers and cameras to track second-by-second melting of small ice balls in water tanks, employing their observations to create equations that can apply to ice bodies of any size.
Through that work, they observed that icebergs are far more active players than expected in the waters in which they float—releasing dense, cold water and jetting across the surface, churning and mixing everything in their paths as they go. The researchers published their findings in Science Advances.
“This is really a first glance at how the meltwater evolves around the ice and how the cooling effect of an ice body creates long-range motion several orders of magnitude larger than the motion produced by melting alone,” Ulloa says. “It gives us insight into what might be happening in a natural system and what kind of processes we should integrate into comprehensive models to understand the role of icebergs in climate and marine ecosystems.”
Even small icebergs are so massive that it might seem challenging to recreate them in a lab space. But Ulloa and Noto conceived of a way: constructing acrylic tanks, lining the bottom with an aluminum plate with temperature sensors, and filling them with about a gallon of temperature-controlled water. Lasers illuminated the tank and two cameras recorded continuously.
The researchers then dropped a one-inch ball of ice into the water and waited. Their set up, in theory, would enable them to quantify the melting in real time and observe how it changed the tank’s water temperature at different depths.
On average, it took about six minutes and 30 seconds for the ice to melt. The meltwater was colder than the water directly surrounding the ice, and cold water was denser than warm water. As the mini-berg melted, the researchers found that regardless of the water’s salinity, meltwater descended in a column, churning the surrounding water and forming a cold, dense layer at the tank’s bottom.
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