研究者たちはグリーンランドの氷の崩壊の後ろに隠された秘密を明らかにします。

2012年に撮影されたこのNASA写真の中央には、グリーンランド北西部のPetermann Glacierが徐々に海に向かって動いており、大きな部分が離れて氷山のように漂流しています。 UCIとNASA JPLの研究者たちは、3つのヨーロッパのミッションで衛星データを使用して、暖かい海水が氷河の地面の移動を引き起こし、急速な悪化を引き起こす方法を見つけました。 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ります。

新しい研究によれば、グリーンランドのピーターマン氷河（Petermann Glacier）の接地線が潮の周期にわたって移動し、暖かい海水が氷の融解速度を高めることができます。 以前に知られていなかったこの相互作用は、モデルに含まれている場合、海洋端氷河の海面上昇の予測を200％増加させる可能性があります。

グリーンランド北西部のPetermann Glacierの研究を行っている間、カリフォルニア大学、Irvine、およびNASAのJet Propulsion Laboratoryの研究者たちは、氷と海が相互作用する以前には見られなかった方法を発見しました。 氷河学者たちは、彼らの発見は、気候コミュニティが極地氷の悪化による将来の海面上昇の規模を大幅に過小評価していることを意味する可能性があると述べました。

3つのヨーロッパのミッション、UCI/[{” 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.