Icebergs melt quite differently than expected | Polarjournal
When icebergs float in the open ocean, they are exposed to winds, waves, and also slowly rising water and air temperatures. These ensure that the iceberg slowly melts and breaks up into smaller pieces. These processes have also been built into climate prediction models, which will be further improved with the findings of Eric Hester and his colleagues. Picture: Michael Wenger

Antarctic icebergs have frequently made the headlines in the world press in recent years, notably without ships being involved. When huge ice giants with an area of several thousand square kilometres break off from the ice shelves, it is not just a media spectacle. Because these giants are made of fresh water, they affect their oceanic environment when they melt. And this also has a climatic impact. A research team has now been able to show for the first time that this melting is not a uniform process. And secondly, the melting is happening much faster than previously assumed. Interestingly, they used small ice cubes for their experiments.

Icebergs and their melting is an important process and is even built into climate models. But until now it was assumed that the melting process on an iceberg is a more or less uniform process. “Previous work incorporating icebergs in climate simulations used very simple melting models.,” explains PhD student and first author of the paper, Eric Hester of the University of Sydney, Australia. “We wanted to see how accurate those were and whether we could improve on them.” Using simulations and experiments with small ice cubes, he and his colleagues were able to show that, for example, the side of an iceberg that is directly hit by the currents melts about twice as fast as the underside. And when an iceberg drifts in the current, melt rates at the exposed front are even between three and four times faster than previously thought. “In icebergs moving in oceans, the melting on the base can be up to 30 percent faster than in old models,” Hester continues. The results of his work were published in the journal Physical Review Fluids.

According to the results of Hester’s work, the shape of icebergs, the so-called aspect ratio, has a significant influence on the melting rate. At first glance, this seems trivial. But this ratio is not the length times the width of an iceberg, it picks up the horizontal extent and submerged depth of a berg. This means that wide icebergs melt much more slowly than narrow icebergs, because they have more underside, which melts more slowly. According to Dr. Geoffrey Vasil, the leader of the study, “Our paper proposes a very simple model that accounts for iceberg shape, as a prototype for an improved model of iceberg melting.” Eric Hester further comments, ” We are confident this modelling captures enough of the complexity so that we now have a much better way to explain how icebergs melt.”

The huge icebergs of Antarctica are mostly broken off from Antarctic ice shelves and drift in the Southern Ocean driven by wind and waves. Melting releases nutrients that then sustain a wide variety of animals around an iceberg. Picture: Michael Wenger

The fact that icebergs are melting faster than previously thought also has implications for climate modelling. However, because the melting of icebergs cannot be measured in the ocean, the results of the international research team are of great importance. This is because icebergs are responsible for around 45 percent of the freshwater influx into the oceans, which in turn influences ocean currents and thus the climate in various regions. This is also important for the ecology, because melting releases nutrients trapped in the ice and the freshwater input changes the chemistry of the surrounding seawater. Icebergs often fertilize their environment in this way and form the basis for their own ecosystem in the Southern Ocean. Experts agree that Eric Hester’s work is important for future climate prediction modeling. His supervisor even goes one step further: “His methods could also be used by astrobiologists to better understand ice moons like Saturn’s Enceladus, a candidate for finding life elsewhere in the Solar System,” Dr Vasil is convinced. In any case, it turns out that the small ice cubes used by Eric Hester and his colleagues were able to wrest one of their secrets from their large relatives in the Southern Ocean.

Dr Michael Wenger, PolarJournal

Link to study: E. W. Hester et al, “Aspect ratio affects iceberg melting,” Phys. Rev. Fluids 6, 023802 (2021).

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