Glace perdue, île trouvée ? La côte orientale de l’Antarctique semble avoir gagné une île

Une île découverte sur la côte Est de l'Antarctique annotée

Île sans nom au large des plates-formes glaciaires Glenzer et Conger en Antarctique de l’Est. 15 novembre 1989 – 9 janvier 2022

Un monticule blanc sans nom au large de l’Antarctique de l’Est semble être une île.

La côte Est de l’Antarctique a perdu la majorité des plateaux de glace Glenzer et Conger. Dans le processus, elle a gagné ce qui est probablement une île. Si cela est confirmé, l’île sans nom ferait partie d’une série d’îles mises à jour ces dernières années suite à la désintégration de certaines parties de la glace flottante qui longe la côte du continent.

L’île candidate est visible dans le triptyque ci-dessus d’images acquises par les satellites Landsat entre 1989 et 2022. Les images sont une combinaison d’infrarouge à ondes courtes et de lumière visible, et ont été ajustées pour assurer la cohérence de la luminosité et des couleurs. Remarquez que l’île a gardé la même forme, même après que les satellites ont pris le relais. glace de plateau détachée et que la glace de mer autour d’elle a augmenté et diminué. Ce monticule rond et blanc n’a pas bougé, même après que de grands icebergs se soient écrasés sur lui suite à l’ouragan .l’effondrement rapide des plateaux de glace Glenzer et Conger. plus tôt cette année.

L’élément semble également plus grand que ses environs. Le profil d’élévation ci-dessous indique qu’au moins une partie de la masse s’élève de 30 à 35 mètres (100 à 115 pieds) au-dessus de la surface de la mer. Les données ont été acquises le 22 décembre 2021 avec le système altimétrique laser topographique avancé (ATLAS) sur ;” data-gt-translate-attributes=”[{” attribute=””>NASA’s Ice, Cloud, and land Elevation Satellite 2 (ICESat-2).

Unnamed Island Eastern Coast of Antarctica

December 22, 2021 – January 9, 2022

But just because a feature acts like an island and looks like an island, does not mean it is an island—at least not in the traditional sense. Scientists are still unsure if there is any solid earth breaching the sea surface below all of the snow and ice.

John Gibson, a scientist with the Australian Antarctic Division, thinks the feature is likely an ice island: a large, heavy cap of ice sitting solidly on an underwater peak. “It is undoubtedly similar to other ice islands, such as Bowman Island,” Gibson said.

Gibson called the ice island “self-perpetuating,” meaning that snow and ice accumulating on the island’s surface balances out the amount of melting that occurs underwater. If that balance becomes disrupted by a decrease in snowfall, then the ice island could thin and float away. “The unnamed island is a more-or-less permanent feature of the landscape,” Gibson said, “but may someday detach from the underlying rock and become an iceberg.”

Without anyone having been there to observe the island, questions remain about its structure. “To be absolutely sure, you would need to put a ship next to it to check for a bedrock outcrop, and maybe a radar over it to assess the ice thickness,” said Christopher Shuman, a University of Maryland, Baltimore County, glaciologist based at NASA’s Goddard Space Flight Center. “The ICESat-2 profile shows that the surface is well above sea level. That would be a whole lot of ‘ice cream’ above the ‘cone’ if there wasn’t bedrock at or above sea level.”

Traditional or ice, the island is the latest in a bunch of similar features that are no longer embedded in Antarctica’s floating glacial ice. In 2019, the U.S. Board on Geographic Names recognized Icebreaker Island, which in 1996 became isolated from the Larsen B Ice Shelf along the Antarctic Peninsula. And in 2020, researchers on a ship-based expedition discovered a small, rocky island capped with ice that may have been part of Pine Island Glacier’s ice shelf.

“The discovery of more of them is likely to continue in the years ahead due to shrinking glacial and sea ice,” Shuman said. “Obviously these are ‘new to us’ features, but we also have more people and more tools to look at the margins of Antarctica now. Several examples do not make a trend, but they do imply that other once-hidden features are likely to be noticed in the years to come.”

NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey, and ICESat-2 data from the National Snow & Ice Center. Story by Kathryn Hansen, with information from Christopher Shuman (NASA GSFC/UMBC JCET).

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