Ice shelves are large platforms of glacial ice floating on the ocean, fed by glaciers. They are found in Antarctica and the Arctic (Greenland, Northern Canada and the Russian Arctic) and are critical to regulate global sea levels.
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The largest in the world is the Ross Ice Shelf – here’s what it is, how it was found and why scientists are watching it so closely.
What is the Ross Ice Shelf?
The Ross Ice Shelf is the largest ice shelf in the world, with an area of roughly 500,809km2 (about the size of Spain) and around 800km across. It floats in the southern portion of Antarctica’s Ross Sea, looming over the surrounding waters.
Several hundred meters thick, the nearly vertical ice front to the open sea is more than 600km long, and between 15-50m high above the water surface. But that’s only a fraction of this giant structure, with 90 per cent of the floating ice hidden below the water.
When was the Ross Ice Shelf discovered?
The Ross Ice Shelf was first sighted on 28th January 1841 by British explorer Sir James Clark Ross, who was searching for the South Magnetic Pole. Encountering the towering wall of ice, Ross realised his ships had nowhere to go – the shelf was originally nicknamed ‘The Barrier’, and later the ‘Great Ice Barrier’.
It went on to become the starting point for some of history’s most famous polar expeditions, including Robert Falcon Scott’s Discovery Expedition in the early 1900s and Roald Amundsen’s successful push to the South Pole in 1911.
Is the Ross Ice Shelf moving?
Despite its size, the Ross Ice Shelf is far from static. Ice flows across the shelf at speeds ranging from 300-1,000 metres per year, constantly pushed forward by the glaciers feeding it from behind. As it advances, it periodically calves enormous icebergs into the Ross Sea – including Iceberg B-15, which broke away in March 2000 as the largest recorded iceberg by area, measuring around 295 by 37 kilometres.
Scientists monitor this movement closely, since a change in the shelf’s speed or stability can be an early signal of how the glaciers behind it – and ultimately global sea levels – might respond.
Is the Ross Ice Shelf important?
Yes, the Ross Ice Shelf is one of the most important pieces in the puzzle of future sea level rise. This giant slab of ice plays a critical role in stabilising the Antarctic ice sheet, essentially acting as a giant natural brake for major glaciers breaking off the mainland.
This is because ice from the interior of Antarctica is constantly flowing outwards via fast-moving glaciers and ice streams. Because ice shelves buttress this outflow by reducing stress at the point where the ice lifts off the land, they act as a plug holding back the glaciers behind them.
Crucially, the ice shelf itself melting away doesn’t directly raise sea levels, since it’s already floating and displacing its own weight in water. The real danger lies in what happens next – the glaciers behind accelerate once the resistance is removed. And then they melt.
Scientists have already seen this play out elsewhere in Antarctica. After the collapse of the smaller Larsen B ice shelf in 2002, nearby glaciers thinned dramatically, with one losing between 16-150m of ice in the following five years.
The Ross Ice Shelf buttresses both the West and East Antarctic Ice Sheet. According to NASA, if the ice shelf collapsed, the resulting flow of glacial ice could eventually raise global sea level by up to 5 metres. That’s enough to completely redraw coastlines around the world.
Is the Ross Ice Shelf melting?
Yes, but not uniformly, and it’s not a fast collapse. Basal melting – ice loss from underneath – happens across most Antarctic ice shelves, driven mainly by warm deep ocean water intruding into the cavity beneath the ice.
On the Ross Ice Shelf specifically, researchers have found an additional, more localised process at play. Near Ross Island, solar-heated surface water seasonally flows into the cavity beneath the shelf, nearly tripling basal melt rates there during the summer months.
For now, the shelf remains relatively stable. But it isn’t invulnerable – which makes ongoing monitoring of the Ross Ice Shelf one of the more closely watched indicators of climate science today.
Top image credit: gyro/Getty Images
