An Antarctic glacier nicknamed the "Doomsday Glacier" because of its potential to contribute to catastrophic sea level rise is melting slower than previously estimated.
But Thwaites Glacier in West Antarctica is still in trouble. Two new studies (opens in new tab) published today (Feb. 15) in the journal Nature (opens in new tab) reveal that while the glacier is insulated from the most rapid melt, portions of its underside have been sculpted into dramatic, crevassed terraces. And these stairstep formations are melting at a rapid clip.
Thwaites glacier sits over a bowl-like depression of bedrock that slopes upward toward the sea, meaning that much of its ice sits below sea level. For that reason, if the glacier retreats too far back it could collapse rapidly, directly contributing to 1.6 feet (0.5 meter) of sea level rise over a few centuries, according to a commentaryl by Craig McConnochie (opens in new tab) accompanying the two new studies. McConnochie studies environmental fluid dynamics at the University of Canterbury in New Zealand but was not involved in the new research.
The two studies were conducted as part of the International Thwaites Glacier Collaboration, a joint U.K. and U.S. effort to measure the Doomsday Glacier. For their study (opens in new tab), researchers drilled a 1,925-foot-deep (587 m) borehole through the glacier's floating section, about 1.2 miles (2 kilometers) from where the glacier is touching the seafloor — known as the glacier's grounding line. They then fixed an instrument 4.9 feet (1.5 m) below the underside of the ice to measure temperature, salt concentrations, velocity of the water flow and melt rate.
The researchers found that over a nine-month observation period, the melt rate of the ice at this relatively horizontal section of the glacier was slower than computer models have predicted, at about 6.5 to 16.4 feet (2 to 5 m) of ice loss per year. The reason for this slower-than-expected melt rate was that the underside of the ice was cushioned by a layer of fresh meltwater.
"This stratification insulates the ice shelf and slows the rate of melting, even though ocean temperatures remain several degrees above the melting point," McConnochie wrote in his editorial.
The borehole also enabled scientists to peer into the underworld of the ice for a second line of research (opens in new tab). Britney Schmidt (opens in new tab), an Earth and atmospheric scientist at Cornell University, and her colleagues used the hole to launch a cylindrical robot called Icefin (opens in new tab) beneath the ice shelf to investigate the difficult-to-reach grounding zone. There, they found that the underside of the ice is not smooth and horizontal but stair-stepped in a series of terraces, with vertical walls up to 19.7 feet (6 m) high. Here, the team also found numerous cracks, known as crevasses, where melting was occurring quickly. At these cracks and vertical surfaces, the team found a melt rate of up to 98.4 feet (30 m) of ice loss per year.
"These new ways of observing the glacier allow us to understand that it’s not just how much melting is happening, but how and where it is happening that matters in these very warm parts of Antarctica," Schmidt said in a statement (opens in new tab). "We see crevasses, and probably terraces, across warming glaciers like Thwaites. Warm water is getting into the cracks, helping wear down the glacier at its weakest points."
And if the Doomsday glacier falls, others nearby will potentially follow, and these could raise sea level by as much as 9.8 feet (3 m) over several thousand years, he wrote.
it snows so much that it starts to collaps on itself and it runs outward, creating glaciers.
it keeps snowing, so the glaciers keeps getting pushed further and further out.
and in this scenario it will eventually hit the ocean, where it will melt, since it is hotter at ocean level than up in the mountains where it originated from, totally natural.
so when a piece containing millions of cubic meter of ice breaks off, there is no need to be worried, because in order for millions of cubic meter of ice to break off, it has to receive millions of cubic meters of snow in order to push the glaciers further away.
So it is a zero sum scenario where nothing was lost and nothing was gained.
The snow is not adding to the glacier as fast as melting is reducing it. The glacier represents thousands of cubic miles worth of water held out of the ocean. If melting continues to exceed deposition, that water flows into the ocean and raises sea levels worldwide.
Ofcourse it is melting. It is warmer at sealevels than up in the mountains.
What do you expect the glacier to do? Just stand still?
It is false to assume that a certain quantity of ice being pushed into the sea requires that same quantity of snow to be deposited at the top.
Ice can only reach 3km high before it collapses under itself and flows outward.
That is not to say that it will stop flowing outward when it comes down to 3km again.
But after getting under 3km, the ice will eventually settle again and build itself up until it gets over 3km again, leading it to not push any more ice out while it is stacking the layers again.