Research shows Antarctica’s Thwaites Glacier could impact sea rise predictions

Researchers 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.

Bill Loguidice June 5, 2024 2 min read

Thwaites Glacier could reshape predictions of sea-level rise.

At 80 miles wide, the Thwaites Glacier in Antarctica is nicknamed the “Doomsday Glacier” for its direct impact on sea-level rise. The Thwaites Glacier Basin measures 74,000 mi², which is roughly the size of Great Britain or Florida. The glacier loses around 50 billion tons of ice per year, contributing to roughly 4% of all sea-level rise worldwide. In the journal, Proceedings of the National Academ y of Sciences, a new study, “Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica,” shows that seawater mixed with freshwater could be contributing to even more glacial melting that before.

The abstract follows.

Rignot, E., Ciracì, E., Scheuchl, B., Tolpekin, V., Wollersheim, M., & Dow, C. (2024). Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica. Proceedings of the National Academy of Sciences, 121(22), e2404766121. https://doi.org/10.1073/pnas.2404766121 — Ocean grounding zone vs. ice grounding zone of an ice sheet/ice shelf system. CDW filling the ice cavity is color coded by temperature from blue (cold) to red (warm). The ocean grounding zone is always flooded with CDW. The ice grounding zone alternates between flooded and unflooded with changes in oceanic tide and atmospheric pressure. Seawater intrusion propagates beyond the ice grounding zone at irregular intervals. On grounded ice, the glacier bed is overlaid by a thin sheet (10 cm) of pressurized subglacial water, which facilitates intrusion and hydraulic jacking of seawater. The panel on the Top shows differential, interferometric fringes associated with ice flexing in the ocean and ice grounding zones at low (Top) and high sea surface height (SSH) (Below). Bull’s eye deformation fringes farther upstream reflect ice subsidence vs. uplift around a bed depression at low vs. high SSH. (Source: PNAS)

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.