Over the 25 years, the scientists calculated almost 67 trillion metric tonnes of ice were exported to the ocean, which were offset by 59 trillion metric tonnes of ice being added to the ice shelves, giving a net loss of 7.5 trillion metric tonnes.
“There is a mixed picture of ice-shelf deterioration, and this is to do with the ocean temperature and ocean currents around Antarctica,” said Benjamin Davison, a research fellow at the University of Leeds, UK, who led the study.
“The western half is exposed to warm water, which can rapidly erode the ice shelves from below, whereas much of East Antarctica is currently protected from nearby warm water by a band of cold water at the coast,” Davison said.
Antarctica is a vast continent and the seas on the western side experience different currents and winds than on the east, and this is driving warmer water underneath the ice shelves on the western flank.
“We expected most ice shelves to go through cycles of rapid, but short-lived shrinking, then to regrow slowly. Instead, we see that almost half of them are shrinking with no sign of recovery,” Davison said. He believes human-induced global warming is likely a key factor in the loss of the ice. If it was due to natural variation in climate patterns, there would have been some signs of ice regrowth on the western ice shelves. Ice shelves float on the seas surrounding Antarctica and are extensions to the ice sheet that covers much of the continent. The ice shelves act as giant “plugs” at the end of glaciers, slowing down the flow of ice draining into the oceans.
When the ice shelves thin or reduce in size, these plugs weaken with the result that the rate of ice lost from the glaciers increases. Some of the biggest ice losses were observed on the Getz Ice Shelf, where 1.9 trillion metric tonnes of ice were lost over the 25-year study period.
Just 5 per cent of those was due to calving, where large chunks of ice breakaway from the shelf and move into the ocean. The rest was due to melting at the base of the ice shelf.
Similarly on the Pine Island Ice Shelf, 1.3 trillion metric tonnes of ice were lost. While about a third of the loss-450 billion metric tonnes-was due to calving, the rest was due to melting from the underside of the ice shelf.
In contrast, the Amery Ice Shelf-on the other side of Antarctica-gained 1.2 trillion metric tonnes of ice. It is surrounded by much colder waters.
The researchers analysed over 1,00,000 satellite radar images to produce this major assessment of the “state of the health” of the ice shelves.
If the ice shelves disappear or even diminish, there will be major knock-on effects for the ice system on Antarctica and for global ocean circulation, the giant “conveyor belt” which moves nutrients as well as heat and carbon from this sensitive polar ecosystem, they added.
