2024-05-20 カリフォルニア大学校アーバイン校(UCI)
＜関連情報＞
- https://news.uci.edu/2024/05/20/uc-irvine-led-team-uncovers-vigorous-melting-at-antarcticas-thwaites-glacier/
- https://www.pnas.org/doi/10.1073/pnas.2404766121
西南極、スウェイツ氷河の接地氷の下に広がる海水の侵入 Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica
Eric Rignot, Enrico Ciracì, Bernd Scheuchl, +2, and Christine Dow
Proceedings of the National Academy of Sciences Published:May 20, 2024
DOI:https://doi.org/10.1073/pnas.2404766121
Significance
We present evidence for seawater intrusions occurring at tidal frequencies over many kilometers beneath the grounded ice of Thwaites Glacier, West Antarctica, a major contributor to sea level rise. The results call into question the traditional approach of modeling a fixed, abrupt transition from grounded ice to ice floating in the ocean with no ice melt at the transition boundary. We delineate a tidally controlled grounding zone, 2 to 6 km in length, and additionally irregular seawater intrusions extending another 6 km inland at spring tide. The rushing of seawater beneath grounded ice over considerable distances makes the glacier more vulnerable to melting from a warmer ocean than anticipated, which in turn will increase projections of ice mass loss.
Abstract
Warm water from the Southern Ocean has a dominant impact on the evolution of Antarctic glaciers and in turn on their contribution to sea level rise. Using a continuous time series of daily-repeat satellite synthetic-aperture radar interferometry data from the ICEYE constellation collected in March–June 2023, we document an ice grounding zone, or region of tidally controlled migration of the transition boundary between grounded ice and ice afloat in the ocean, at the main trunk of Thwaites Glacier, West Antarctica, a strong contributor to sea level rise with an ice volume equivalent to a 0.6-m global sea level rise. The ice grounding zone is 6 km wide in the central part of Thwaites with shallow bed slopes, and 2 km wide along its flanks with steep basal slopes. We additionally detect irregular seawater intrusions, 5 to 10 cm in thickness, extending another 6 km upstream, at high tide, in a bed depression located beyond a bedrock ridge that impedes the glacier retreat. Seawater intrusions align well with regions predicted by the GlaDS subglacial water model to host a high-pressure distributed subglacial hydrology system in between lower-pressure subglacial channels. Pressurized seawater intrusions will induce vigorous melt of grounded ice over kilometers, making the glacier more vulnerable to ocean warming, and increasing the projections of ice mass loss. Kilometer-wide, widespread seawater intrusion beneath grounded ice may be the missing link between the rapid, past, and present changes in ice sheet mass and the slower changes replicated by ice sheet models.
