Feb 17 2021
According to a new study by the University of Sydney mathematicians, icebergs are melting quicker compared to what existing models predict. Hence, they have suggested a new model for a more precise representation of the melting speed of icebergs into oceans.
Eric Hester (right) and his PhD supervisor Dr Geoffrey Vasil from the School of Mathematics at the University of Sydney. Image Credit: Louise Cooper/University of Sydney.
Published in the Physical Review Fluids journal, the study findings have implications for climate scientists and oceanographers.
While icebergs are only one part of the global climate system, our improved model provides us with a dial that we can tune to better capture the reality of Earth's changing climate.
Eric Hester, Study Lead Author and PhD Student, University of Sydney
Existing models that are integrated into the methodology employed by the Intergovernmental Panel on Climate Change presume that icebergs melt evenly in ocean currents. But Mr Hester and his collaborators have demonstrated that icebergs do not melt evenly but at different speeds based on their shape.
About 70 percent of the world’s freshwater is in the polar ice sheets and we know climate change is causing these ice sheets to shrink. Some of this ice loss is direct from the ice sheets, but about half of the overall ice loss from Greenland and Antarctica happens when icebergs melt in the ocean, so understanding this process is important. Our model shows that icebergs are melting at faster rates than current models assume.
Eric Hester, Study Lead Author and PhD Student, University of Sydney
Mr Hester is a doctoral student at the University of Sydney School of Mathematics and Statistics.
In addition to its significance for modeling how ice sheets are transforming, Mr Hester notes that the study will help gain better insights into the effect of ice melt on ocean currents.
“Ocean circulation is the reason that Britain isn't as cold as Alberta, Canada, despite being at similar latitudes,” added Mr Hester.
According to him, the Gulf Stream that takes warmer water from the tropics throughout the Atlantic keeps Western Europe warmer compared to how it otherwise would be.
“That current could shut down if too much freshwater is dumped into the system at once, so it's critical we understand the process of iceberg and ice sheet melt.”
Where and when the freshwater is discharged, and how the ocean is impacted, is partially based on the melt speed of the icebergs.
Previous work incorporating icebergs in climate simulations used very simple melting models. We wanted to see how accurate those were and whether we could improve on them.
Dr Geoffrey Vasil, Study Co-Author, University of Sydney
Mr Hester noted that their models—verified in the experiment—and the observations of oceanographers indicate that the sides of icebergs melt around twice as fast as their base. In the case of icebergs that constantly move in the ocean, melting at the front can be three or four times quicker compared to what was forecast by the previous models.
“The old models assumed that stationary icebergs didn't melt at all, whereas our experiments show melting of about a millimetre every minute. In icebergs moving in oceans, the melting on the base can be up to 30 percent faster than in old models,” added Mr Hester.
The study demonstrates that the iceberg shape is crucial. Since the sides tend to melt quicker, wider icebergs melt more gradually but smaller and narrower icebergs melt quicker.
According to Dr Vasil, “Our paper proposes a very simple model that accounts for iceberg shape, as a prototype for an improved model of iceberg melting.”
The team tested such models by developing the first realistic small-scale simulations of melting ice in saltwater.
“We are confident this modelling captures enough of the complexity so that we now have a much better way to explain how icebergs melt,” stated Mr Hester.
Dr Vasil, who is Mr Hester’s PhD supervisor, notes: “Before Eric started his PhD the computational tools to model these kinds of systems didn't really exist. Eric took a very simple prototype and made it work wonderfully on the complex ice-melting problem.”
Dr Vasil added that these techniques apply to several other systems, such as the melting of frozen, saline sea ice or glaciers.
“But it doesn’t end there. 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,” explained Dr Vasil.
The study was performed jointly with researchers from the British Antarctic Survey, the University of Canterbury in New Zealand, and the Woods Hole Oceanographic Institution in Massachusetts, USA.
Journal Reference:
Hester, E. W., et al. (2021) Aspect ratio affects iceberg melting. Physical Review Fluids. doi.org/10.1103/PhysRevFluids.6.023802.