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2012 年に撮影されたこの NASA の写真の中央では、グリーンランド北西部のピーターマン氷河が徐々に海に向かって移動しており、大きな部分が壊れて氷山として漂流しています。 UCIとNASA JPLの研究者らは、3つの欧州ミッションからの衛星データを使用して、暖かい海水がどのように氷河の接地線の移動を引き起こし、氷河の急速な劣化につながっているかを調べた。 クレジット: NASA
研究によると、将来の海面上昇の程度は大幅に過小評価される可能性がある。
新しい研究により、グリーンランドのピーターマン氷河の接地線が潮汐周期中に移動し、暖かい海水によって氷の融解が促進されることが判明した。 このこれまで知られていなかった相互作用がモデルに含まれている場合、海端の氷河の海面上昇予測が 200% 増加する可能性があります。
カリフォルニア大学アーバイン校とNASAのジェット推進研究所の研究者らは、グリーンランド北西部のピーターマン氷河の研究を行っている間に、氷と海洋が相互作用するこれまで見たことのない方法を発見した。 氷河学者らは、彼らの発見は、気候変動コミュニティが極地の氷の劣化によって引き起こされる将来の海面上昇の大きさを大幅に過小評価していたことを意味する可能性があると述べた。
3 つの欧州ミッション、UCI/の衛星レーダー データを使用[{” attribute=””>NASA team learned that Petermann Glacier’s grounding line – where ice detaches from the land bed and begins floating in the ocean – shifts substantially during tidal cycles, allowing warm seawater to intrude and melt ice at an accelerated rate. The group’s results are the subject of a paper published on May 8 in Proceedings of the National Academy of Sciences.
“Petermann’s grounding line could be more accurately described as a grounding zone, because it migrates between 2 and 6 kilometers as tides come in and out,” said lead author Enrico Ciraci, UCI assistant specialist in Earth system science and NASA postdoctoral fellow. “This is an order of magnitude larger than expected for grounding lines on a rigid bed.”
He said the traditional view of grounding lines beneath ocean-reaching glaciers was that they did not migrate during tidal cycles, nor did they experience ice melt. But the new study replaces that thinking with knowledge that warm ocean water intrudes beneath the ice through preexisting subglacial channels, with the highest melt rates occurring at the grounding zone.
The researchers found that as Petermann Glacier’s grounding line retreated nearly 4 kilometers – 2½ miles – between 2016 and 2022, warm water carved a 670-foot-tall cavity in the underside of the glacier, and that abscess remained there for all of 2022.
“These ice-ocean interactions make the glaciers more sensitive to ocean warming,” said senior co-author Eric Rignot, UCI professor of Earth system science and NASA JPL research scientist. “These dynamics are not included in models, and if we were to include them, it would increase projections of sea level rise by up to 200 percent – not just for Petermann but for all glaciers ending in the ocean, which is most of northern Greenland and all of Antarctica.”
The Greenland ice sheet has lost billions of tons of ice to the ocean in the past few decades, the PNAS paper stresses, with most of the loss caused by warming of subsurface ocean waters, a product of Earth’s changing climate. Exposure to ocean water melts the ice vigorously at the glacier front and erodes resistance to the movement of glaciers over the ground, causing the ice to slide more quickly to the sea, according to Rignot.
Reference: “Melt rates in the kilometer-size grounding zone of Petermann Glacier, Greenland, before and during a retreat” by Enrico Ciracì, Eric Rignot, Bernd Scheuchl, Valentyn Tolpekin, Michael Wollersheim, Lu An, Pietro Milillo, Jose-Luis Bueso-Bello, Paola Rizzoli and Luigi Dini, 8 May 2023, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2220924120
Ciraci’s research was supported by the NASA Postdoctoral Program at the Jet Propulsion Laboratory. Joining Ciraci and Rignot on the project were Bernd Scheuchl, UCI associate project scientist; Valentyn Tolpekin and Michael Wollersheim of Finland’s Iceye mission; Lu An of China’s Tongji University; Pietro Milillo of the University of Houston; Jose-Luis Bueso-Bello of the German Aerospace Center; and Luigi Dini of the Italian Space Agency.
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