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Icebergs don't melt the way scientists' models have said they do – but an upgrade, taking into account previously ignored factors, is now available. The refinement isn't important for the reasons you might immediately think – it doesn't really affect models of sea-level rise – but it could have other very significant implications.
Physicists have been gazing at ice cubes melting into their whiskey or soda long enough that you'd think it would have inspired a thousand grant applications. However, University of Sydney PhD student Eric Hester said in a statement when scientists modeled the rate at which icebergs melt, their “Models assumed that stationary icebergs didn’t melt at all.”
This obviously nonsensical assumption came about because the models were originally developed to investigate the feasibility of towing icebergs from the Antarctic to water the deserts of Australia and Chile, Hester told IFLScience. Since the modelers were concerned about the melting rate of icebergs in motion, they didn't worry about getting the maths right for those that were not moving, particularly since this was before computers made complex calculations less daunting. In the absence of anything better, iceberg modelers – a niche field, to say the least – have been using equations they knew were wrong ever since.
Hester has addressed this in Physical Review Fluids. “You need to keep track of how fast the water is moving, how salty it is, its temperature and the shape of the iceberg,” Hester told IFLScience. “Old models only looked at temperature and water movement.”
Hester found icebergs often melt a lot faster than the models anticipated, and the shape is the particularly important part. He found icebergs melt from the sides about twice as fast as from the base, and most rapidly of all at the front if moving relative to the surrounding water. Consequently, deep but narrow icebergs melt faster than wide, flat ones. Hester and co-authors provided equations for melt rates that take these things into account.
Once an iceberg has calved off a glacier it is already floating and, by the principle known since Archimedes, raises the oceans' volume. How fast it melts does not change that, unlike for ice supported on land. However, Hester's work still has important climate implications. The injection of too much freshwater into the North Atlantic has turned off the ocean circulation, particularly the Gulf Stream, in the past, causing Northern European temperatures to plummet. A repetition could see England's climate resemble that of barely inhabited Labrador – which is at the same latitude – even as the rest of the planet heats up. Understanding how fast icebergs melt could help us predict how likely this is to happen.
The tools Hester has provided could also be useful for understanding the melting of glaciers that extend out into the oceans, causing the calving of icebergs in the first place. More exotically, they can help us understand moons like Enceladus and Europa where ice sheets sit above internal oceans, making them possibly the best places to look for life in the Solar System.
