West Antarctica

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West Antarctica

Postby HBS Guy » 07 Oct 2017, 08:04

This ice sheet, drained by glaciers flowing into the Amundsen Sea have accelerated and will increase sea level rise. the two main glaciers are the Pine Island glacier and the Thwaites glacier. If these go the rest of the West Antarctic icesheet will go too.

Warmer waters entering the ocean around Antarctica are undermining these glaciers. On the Antarctic Peninsula these warmer waters have melted the ice sheets so now the glaciers are exposed to these warmer waters where they meet the sea.

Having set the scene, here are some details of accelerated glacier retreat.

A NASA study has located the Antarctic glaciers that accelerated the fastest between 2008 and 2014 and finds that the most likely cause of their speedup is an observed influx of warm water into the bay where they're located.
The water was only 1 to 2 degrees Fahrenheit (0.5 to 1 degree Celsius) warmer than usual water temperatures in the area, but it increased the glaciers' flow speeds by up to 25 percent and multiplied the rate of glacial ice loss by three to five times—from 7 to 10 feet of thinning per year (2 to 3 meters) up to 33 feet per year (10 meters).

Researchers at NASA's Jet Propulsion Laboratory in Pasadena, California, found that the warmer water was driven into the area by winds associated with two global climate patterns: La Niña and the less-known Southern Annular Mode, which involves a change in location of the belt of winds that encircles Antarctica. The glaciers' acceleration lasted from mid-2008 to 2012. After that, they slowed down but have continued to flow faster than they did before the warm water arrived.

We are due to get another La Nina later this year (presently in the neutral phase) so I guess we can expect further acceleration of glacier retreat?

The four glaciers are in Marguerite Bay on the western side of the Antarctic Peninsula. Before 2008, their flow rates and rates of thinning (a measure of ice loss) had been stable for almost two decades—since the Wordie Ice Shelf in front of the glaciers collapsed in about 1989. The collapse broke off almost all of the floating portions of the glaciers, leaving the parts that are grounded on bedrock.

"Grounded ice is a major concern for sea level rise, because it hasn't contributed to sea level yet," said the new study's lead author, Catherine Walker of JPL. "Floating ice has already made its contribution to the sea level."

Antarctica used to be protected from AGW by strong circumpolar winds and currents. No more!

To find out what caused the speedup, Walker and Gardner checked air temperatures over the bay and saw that, though they had generally warmed over past decades, they hadn't spiked markedly in 2008 to 2012.

Water temperatures were a different story. A long-term data set from the nearby U.S. Antarctic Program's Palmer Station showed that warmer water first appeared in the bay in 2008, peaked in 2009, and stayed there almost nonstop through 2011. Using an analysis of winds in the area from the U.S. ECCO (Estimating the Circulation and Climate of the Ocean) project, Walker and Gardner showed that northwesterly winds allowed this warmer water to well up from the deep ocean onto the continental shelf in front of Marguerite Bay. Currents then carried the warm water into the bay and up to the fronts of the glaciers.

While the warm water was in the bay, there was a moderately strong La Niña event, and the belt of winds circling Antarctica was closer to the continent rather than farther north—a condition known as the positive phase of the Southern Annular Mode (SAM). The combination of these two climate patterns was responsible for the northwesterly winds along the western side of the Antarctic Peninsula.

The speed at which the Marguerite Bay glaciers responded to a relatively small increase in ocean temperature was startling, Walker said. "We detected the warmest water first in January 2009, and by November the glaciers were already losing ice at a rate of eight meters [25 feet] per year in thickness."

Walker noted that while these glaciers accelerated during a La Niña event, the nearby Pine Island Glacier, one of West Antarctica's fastest-moving glaciers, melts faster during El Niños—the opposite climate pattern. She said, "This alternating response to global atmospheric patterns underscores the need to improve our understanding of the links between global climate and changes in the polar oceans."


Journal reference: https://phys.org/news/2017-09-revved-antarctic-glaciers.html

Little denialist morons like Booby crap on about volcanoes doing the melting etc. Nonsense. At best what volcanoes there are might cause some melting deep under the ice and so “lubricate” the movement of the ice but are not a cause of it. The causes of glacier retreat are warmer sea and/or air temperatures and those are due to AGW and the changes in winds and currents that it causes! Some of those bring polar conditions to middle latitudes and snake oil salesmen then claim this is “proof” of an ice age. :WTF
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Re: West Antarctica

Postby HBS Guy » 13 Oct 2017, 12:35

Apparently under the ice shelves there are “upside down canyons:”

A mysterious world of upside-down canyons crisscrosses the underbelly of Antarctica's ice shelves.

Now, research finds that some of these crevasses may contribute to both the thinning of the shelves and sea-level rise. A single canyon in the Dotson ice shelf in West Antarctica is responsible for dumping 4.4 billion short tons (4 billion metric tons) of freshwater into the Southern Ocean, according to Noel Gourmelen, a remote-sensing researcher at The University of Edinburgh.

The ice shelf location:
So the shelf is “holding back” glaciers draining part of the West Antarctic ice sheet.

Both of these satellites use radar techniques to gauge ice-shelf thickness and dynamics. The team used the data to investigate the flow of the Dotson ice shelf, a 30-mile-wide (50 kilometers) expanse off the remote coast of Marie Byrd Land.

"We have found subtle changes in both surface elevation data from CryoSat and ice velocity from Sentinel-1, which shows that melting is not uniform, but has centered on a 5-km-wide [3 miles] channel that runs 60 km [37 miles] along the underside of the shelf," Gourmelen said in a statement.

So thinning is going on much faster than we have realised. That nine metre sea level rise just got a bit closer!
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