West Antarctica is in a lot of trouble, which means that we too, are in a lot of trouble from sea level rise.
The West Antarctic Ice Sheet (WAIS) is the largest mass of ice on the planet.covering an area of 5,405,430 square miles and holding 30 million cubic km of ice. That represents 90% of the world’s fresh water and also holds 230 feet of sea level rise. East Antarctica rests on the bedrock. In West Antarctica the bed can extend to more than 8200 feet below sea level.
Washington University in Saint Louis reports on the geography of West Antarctica.
"Our understanding of what's going on is really hampered because we can't see the geology," said Andrew Lloyd, a graduate student in earth and planetary sciences in Arts & Sciences at Washington University in St. Louis. "We have to turn to geophysical methods, such as seismology, to learn more," he said.
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The old rock of East Antarctica rises well above sea level, but west of the Transantarctic Mountains, extension has pulled the crust into a broad saddle, or rift valley, much of which lies a kilometer below sea level.
“If you removed the ice, West Antarctica would rebound, and most of it would be near sea level. But the narrower and deeper basins might remain below it,” Lloyd said. “The Bentley Subglacial Trench, which is the lowest point on Earth not covered by an ocean, would still be a kilometer and a half below sea level if the ice were removed.”
Scientists have not detected earthquakes which means the rift is inactive. But heat was found that suggests that the rifting had stopped only recently.
The rift system is thought to have a major influence on ice streams in West Antarctica. “Rifting and ice flow occur on completely different time scales,” Lloyd said, “so rifting is not going to suddenly make the ice sheet unstable.
“But to accurately model how quickly the ice is going to flow or the rock to rebound, we need to understand the ‘boundary conditions’ for ice models, such as heat flow from the mantle,” he said.
Ohio State University reported in late 2013 that East Antarctica is sliding sideways.
The discovery comes from researchers led by The Ohio State University, who have recorded GPS measurements that show West Antarctic bedrock is being pushed sideways at rates up to about twelve millimeters--about half an inch--per year. This movement is important for understanding current ice loss on the continent, and predicting future ice loss.
Half an inch doesn't sound like a lot, but it's actually quite dramatic compared to other areas of the planet, explained Terry Wilson, professor of earth sciences at Ohio State. Wilson leads POLENET, an international collaboration that has planted GPS and seismic sensors all over the West Antarctic Ice Sheet.
Scientists were not caught off guard as to horizontal motion. But they were surprised to find the bedrock moving towards the regions of greatest ice loss, the West Antarctic ice sheet.
"From computer models, we knew that the bedrock should rebound as the weight of ice on top of it goes away," Wilson said. "But the rock should spread out from the site where the ice used to be. Instead, we see movement toward places where there was the most ice loss."
The seismic sensors explained why. By timing how fast seismic waves pass through the earth under Antarctica, the researchers were able to determine that
the mantle regions beneath east and west are very different. West Antarctica contains warmer, softer rock, and East Antarctica has colder, harder rock.
Stephanie Konfal, a research associate with POLENET, pointed out that where the transition is most pronounced, the sideways movement runs perpendicular to the boundary between the two types of mantle.
She likened the mantle interface to a pot of honey.
"If you imagine that you have warm spots and cold spots in the honey, so that some of it is soft and some is hard," Konfal said, "and if you press down on the surface of the honey with a spoon, the honey will move away from the spoon, but the movement won't be uniform. The hard spots will push into the soft spots. And when you take the spoon away, the soft honey won't uniformly flow back up to fill the void, because the hard honey is still pushing on it."
Or, put another way, ice compressed West Antarctica's soft mantle. Some ice has melted away, but the soft mantle isn't filling back in uniformly, because East Antarctica's harder mantle is pushing it sideways. The crust is just along for the ride.
Science Daily reports on a new discovery on an active hydrological system of water conduits and sediment ridges below the Antarctic ice sheet. It had been thought that warm water was carving the ice shelf’s from below leading to the deterioration and collapse of the ice shelf. But according to the study prepared by Université libre de Bruxelles and published in the journal Nature, that is only part of the story. The carved tunnels that allow warm ocean water deep into the ice can originate on land as well as the sea bed, and that the size of the channel is determined by how large the landform was when it carved into the ice.
Subglacial conduits form under large ice sheets as part of their basal hydrological system. These tunnels have a typical diameter of several meters to tens of meters, and they funnel the subglacial melt water towards the ocean. However, new geophysical observations by the Laboratoire de Glaciologie of the ULB show that these conduits widen considerably the closer they come to the ocean. A new mathematical model explains this widening with the vanishing overburden pressure at the location where the ice becomes afloat on the ocean.
As the conduits widen, the outflow velocity of the subglacial water decreases, which leads to increased sediment deposition at the conduit's portal. Over thousands of years, this process builds up giant sediment ridges -- comparable in height with the Eiffel tower -- below the ice. Active sedimentation in subglacial water conduits seems to drive the formations of Eskers -- elongated ridges of gravel which are commonly observed today in areas where former ice sheets have retreated. However, the remainders of today's Eskers are considerably smaller in size than those now discovered in Antarctica.
The evolving sediment ridges leave scars at the bottom of the ice as the ice flows over them. These scars are transmitted to the floating ice shelves farther downstream forming ice-shelf channels. Ice in these channels is up to half as thin as their surroundings, making them a weak spot when exposed to melting from the warmer ocean. It was originally thought that ice-shelf channels are carved by melting due to the ocean only, but this seems only part of the story: "Our study shows that ice-shelf channels can already be initiated on land, and that the size of the channels significantly depends on sedimentation processes occurring over hundreds to thousands of years" indicates Reinhard Drews, lead author of the study.
I had hoped that the Trump distraction would pause, at least briefly, and the media just might report on the news that our polar regions are unravelling. But as usual, the slow drip of news on the POTUS’s corruption and the stench of treason sucks all of the oxygen out of the room. But climate change, just like gravity, doesn’t care whether the media informs the citizenry on the rapid rate of global warming or not. It just is. Trump’s, and the media’s, lack of leadership on this existential crisis is stunning.