By Paul Homewood
From the “We’re all going to drown department”:
Scientists have found a new point of major vulnerability in the Antarctic ice sheet, in a region that already appears to be changing as the climate warms and has the potential to raise sea levels by nearly five feet over the long term.
Denman glacier, in East Antarctica, is a 12-mile-wide stream of ice that flows over the deepest undersea canyon in the entire ice sheet before spilling out into the ocean. That subsea trough is more than 2 miles deep, or double the average depth of the Grand Canyon. While there are far deeper trenches in the open ocean, such as the Marianas Trench, in this case the extreme undersea topography lies right on the outer fringe of the Antarctic continent — making it the “deepest continental point on Earth.”
That deep canyon is a potential pathway for the ocean to infiltrate deep into Antarctica’s center — posing a threat of significant sea level rise.
Denman glacier, which fills the submerged canyon with extremely thick ice, has begun to respond to climate change. It is creeping backward down a slope that plunges into these extreme depths, new research finds, potentially igniting a feedback process that could ultimately unload trillions of tons of ice into the ocean
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“The configuration of the bed of the glacier makes this one of the weakest spots in east Antarctica,” said Virginia Brancato, a NASA scientist who was the lead author of the new study in Geophysical Research Letters. “If I have to look at East Antarctica as a whole, this is the most vulnerable spot in the area.”….
The study used satellite techniques to determine the “grounding line” of Denman glacier has retreated inland more than 3 miles toward the center of Antarctica in the past 20 years.
The “grounding line” of a marine glacier, such as Denman, is the point deep beneath the sea surface where ocean, bedrock and ice all meet. Farther outward from the grounding line, the ice is afloat and no longer touching bedrock. Farther inland, the ice no longer has contact with the ocean.
If a grounding line is moving backward, more ice is floating, and the ocean is penetrating further inland with the glacier in retreat. That’s what’s happening at Denman, scientists say.
In this case, the grounding line has not only moved backward, but it has also moved down a steep slope into the two-mile-deep canyon atop which the glacier sits. This means the ice front that the glacier presents to the ocean has gotten thicker. It is more than a mile thick, but it has the potential to increase to two miles of thickness if the glacier backs fully into the depths.
Scientists describe this type of glacier configuration as a “retrograde slope” and have determined it can lead to a runaway feedback process in which ice loss begets more and more ice loss. The more the glacier’s grounding line backs down the slope, the thicker the ice becomes. This means the ice can flow outward faster and also that more of it will be exposed to ocean waters capable of melting it.
“In this configuration, it means that once the glacier starts retreating, it’s very hard to stop it,” said Eric Rignot of the University of California, Irvine, one of the study’s authors. “You sort of open the floodgates.”
Elephant seals fitted with sensors on their heads have been used to take measurements of the water temperatures off the coast of Denman glacier. The resulting readings show temperatures more than sufficient to melt ice, around -1 degrees Celsius, in the ocean offshore at about 300 meters of depth. If that water is making its way beneath the glacier’s floating portion, its “ice tongue,” and all the way to the grounding line, the melting potential would be high and explain why Denman already is in retreat.
“We have the indirect signature of that warm water by the fact that the ice is melting from the bottom at relatively high rates compared to the rest of East Antarctica,” said Rignot.
Denman already has lost over 250 billion tons of ice, researchers have calculated, equivalent to a little over half a millimeter of sea level rise. But there are 540 trillion tons of ice loss potential if the glacier were to travel backward across the entire subterranean canyon — a distance of nearly 100 miles. At this point, the melting could then reach a critical area of Antarctica called the Aurora Subglacial Basin.
Here, enormous volumes of ice rest on a bed well below sea level. If the ocean gets into the Aurora Basin due to the loss of Denman glacier, there is the potential for nearly five feet of sea level rise.
It’s unclear how fast this dynamic could play out. In a region with a complex and little understood undersea topography, it’s unknown how much warm water is making it to the base of Denman, and that makes a huge difference, said Donald Blankenship, a glaciologist at the University of Texas at Austin who has conducted extensive research on East Antarctica.
https://www.washingtonpost.com/climate-environment/2020/03/23/denman-glacier-climate-change/
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Paul Homewood responds:
It’s hard to know where to start with this nonsense.
For a start, it is implied that the recent retreat of the glacier is linked to a warming climate. However, the climate has actually been getting colder in that part of Antarctica during the period of the study, which begins in 1979:
https://data.giss.nasa.gov/tmp/gistemp/STATIONS/tmp_AYM00089611_14_0_1/station.png
The point is admitted that it is actually warm water at a depth of about 300m which is undercutting the glacier. But it is physically impossible for greenhouse gases to have any measurable effect at all on waters at such a depth.
But what is measurable is that sea surface temperatures are currently colder than average all around Antarctica:
https://www.ospo.noaa.gov/data/sst/anomaly/2020/anomnight.3.12.2020.gif
In reality the scientists who wrote this study do not have a clue whether the retreat of the Denman is anything new or not, or whether the deep ocean temperatures are any warmer than before 1979. Or whether what they are observing is just a natural process.
We can then go on to explore sea level implications.
They claim that since 1979, 250 billion tonnes of ice has been lost, equivalent to 0.5mm of sea level rise. In other words, 1.3mm/C, hardly cataclysmic.
They then go on to talk about a potential loss of 540 trillion tonnes, raising sea levels by 5 feet. Yet at current rates, it would take 2160 years for this to occur!
As always with these sort of studies, the authors refuse to say how long all this will take to happen.
But it gets even more absurd!
Look again at the topography of the Denman Glacier:
It is reckoned to be 11500 feet deep, the deepest point on continental Earth apparently.
Yet the canyon comes to a halt roughly at the place where the glacier ends. In other words, most of the ice locked into the canyon cannot simply escape into the ocean, as it would have to flow uphill.
Even if it all melts, as a result of the inflow of warmer ocean water, the ice in the canyon will simply be replaced by water. Crucially, this means that sea levels cannot rise as a result. This can only happen when ice on land enters the sea.
