Hexbyte Glen Cove Pine Island Glacier's ice shelf is ripping apart, speeding up key Antarctic glacier thumbnail

Hexbyte Glen Cove Pine Island Glacier’s ice shelf is ripping apart, speeding up key Antarctic glacier

Hexbyte Glen Cove

Pine Island Glacier ends in an ice shelf that floats in the Amundsen Sea. These crevasses are near the grounding line, where the glacier makes contact with the Antarctic continent. The photo was taken in January 2010 from the east side of the glacier, looking westward. This ice shelf lost one-fifth of its area from 2017 to 2020, causing the inland glacier to speed up by 12%. Credit: Ian Joughin/University of Washington

For decades, the ice shelf helping to hold back one of the fastest-moving glaciers in Antarctica has gradually thinned. Analysis of satellite images reveals a more dramatic process in recent years: From 2017 to 2020, large icebergs at the ice shelf’s edge broke off, and the glacier sped up.

Since floating ice shelves help to hold back the larger grounded mass of the glacier, the recent speedup due to the weakening edge could shorten the timeline for Pine Island Glacier’s eventual collapse into the sea. The study from researchers at the University of Washington and British Antarctic Survey was published June 11 in the open-access journal Science Advances.

“We may not have the luxury of waiting for slow changes on Pine Island; things could actually go much quicker than expected,” said lead author Ian Joughin, a glaciologist at the UW Applied Physics Laboratory. “The processes we’d been studying in this region were leading to an irreversible collapse, but at a fairly measured pace. Things could be much more abrupt if we lose the rest of that ice shelf.”

Pine Island Glacier contains approximately 180 trillion tons of ice—equivalent to 0.5 meters, or 1.6 feet, of . It is already responsible for much of Antarctica’s contribution to sea-level rise, causing about one-sixth of a millimeter of sea level rise each year, or about two-thirds of an inch per century, a rate that’s expected to increase. If it and neighboring Thwaites Glacier speed up and flow completely into the ocean, releasing their hold on the larger West Antarctic Ice Sheet, global seas could rise by several feet over the next few centuries.

These have attracted attention in recent decades as their thinned because warmer ocean currents melted the ice’s underside. From the 1990s to 2009, Pine Island Glacier’s motion toward the sea accelerated from 2.5 kilometers per year to 4 kilometers per year (1.5 miles per year to 2.5 miles per year). The glacier’s speed then stabilized for almost a decade.

Results show that what’s happened more recently is a different process, Joughin said, related to internal forces on the glacier.

From 2017 to 2020, Pine Island’s ice shelf lost one-fifth of its area in a few dramatic breaks that were captured by the Copernicus Sentinel-1 satellites, operated by the European Space Agency on behalf of the European Union. The researchers analyzed images from January 2015 to March 2020 and found that the recent changes on the ice shelf were not caused by processes directly related to ocean melting.







The ice shelf on Antarctica’s Pine Island Glacier lost about one-fifth of its area from 2017 to 2020, mostly in three dramatic breaks. The timelapse video incorporates satellite images from January 2015 to March 2020. For most of the first two years, the satellite took high-resolution images every 12 days; then for more than three years it captured images of the ice shelf every six days. Images are from the Copernicus Sentinel-1 satellites operated by the European Space Agency on behalf of the European Union. Credit: Joughin et al./Science Advances

“The ice shelf appears to be ripping itself apart due to the glacier’s acceleration in the past decade or two,” Joughin said.

Two points on the glacier’s surface that were analyzed in the paper sped up by 12% between 2017 and 2020. The authors used an ice flow model developed at the UW to confirm that the loss of the ice shelf caused the observed speedup.

“The recent changes in speed are not due to melt-driven thinning; instead they’re due to the loss of the outer part of the ice shelf,” Joughin said. “The glacier’s speedup is not catastrophic at this point. But if the rest of that ice shelf breaks up and goes away then this glacier could speed up quite a lot.”

It’s not clear whether the shelf will continue to crumble. Other factors, like the slope of the land below the glacier’s receding edge, will come into play, Joughin said. But the results change the timeline for when Pine Island’s ice shelf might disappear and how fast the glacier might move, boosting its contribution to rising seas.

“The loss of Pine Island’s ice shelf now looks like it possibly could occur in the next decade or two, as opposed to the melt-driven subsurface change playing out over 100 or more years,” said co-author Pierre Dutrieux, an ocean physicist at British Antarctic Survey. “So it’s a potentially much more rapid and abrupt change.”

Pine Island’s ice shelf is important because it’s helping to hold back this relatively unstable West Antarctic glacier, the way the curved buttresses on Notre Dame cathedral hold up the cathedral’s mass. Once those buttresses are removed, the slow-moving glacier can flow more quickly downward to the ocean, contributing to rising seas.

“Sediment records in front of and beneath the Pine Island indicate that the glacier front has remained relatively stable over a few thousand years,” Dutrieux said. “Regular advance and break-ups happened at approximately the same location until 2017, and then successively worsened each year until 2020.”



More information:
Ice-shelf retreat drives recent Pine Island Glacier speedup, Science Advances (2021). DOI: 10.1126/sciadv.abg3080 , advances.sciencemag.org/content/7/24/eabg3080

Citation:
Pine Island Glacier’s ice shelf is ripping apart, speeding up key Antarctic glacier (2021, June 11)
retrieved 12 June 2021
from https://phys.org/news/2021-06-island-glacier-ice-shelf-ripping.html

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Hexbyte Glen Cove Galapagos island gets 36 endangered giant tortoises thumbnail

Hexbyte Glen Cove Galapagos island gets 36 endangered giant tortoises

Hexbyte Glen Cove

The International Union for Conservation of Nature (IUCN) lists the Chelonoidis chatamensis, or San Cristobal Giant Tortoise, as endangered, though their numbers are on the rise

Three dozen endangered giant tortoises, born and raised in captivity, have been released into the wild on one of the Galapagos islands, where their kind is from.

The Galapagos National Park said the 36 creatures were freed on the northeastern part of San Cristobal island, where an estimated 6,700 roam free.

The latest additions belong to the Chelonoidis chathamensis subspecies—one of 15 endemic to the Galapagos, where Charles Darwin’s observation of birds and tortoises on different islands led to his theory of natural selection.

The youngsters are between six and eight years old, and weigh between three and five kilograms (6.6-11 pounds) each.

The animals spent time in quarantine and were tested for disease and parasites before their release so as not to endanger the rest of the natives, the park said.

The International Union for Conservation of Nature (IUCN) lists Chelonoidis chathamensis, or San Cristobal Giant Tortoise, as endangered, though their numbers are on the rise.

The slow-breeding creatures can live to the age of about 100 or 150 and are endemic to the Galapagos Islands in the Pacific Ocean off Ecuador’s coast.

According to the IUCN, the San Cristobal Giant Tortoise population experienced “catastrophic decline” due to the introduction of predators, competitors and vegetation change—from about 24,000 animals historically to about 500-700 in the early 1970s.

By 2016, the numbers had recovered somewhat to about 6,700.

In the last eight years, 75 of the sub-species, raised in captivity, have been reintroduced to San Cristobal.



© 2021 AFP

Citation:
Galapagos island gets 36 endangered giant tortoises (2021, March 4)
retrieved 5 March 2021
from https://phys.org/news/2021-03-galapagos-island-endangered-giant-tortoises.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

Read More Hexbyte Glen Cove Educational Blog Repost With Backlinks —