Thwaites Glacier, a massive and rapidly changing ice mass in West Antarctica, is a significant component of the West Antarctic Ice Sheet. Its dynamic behavior makes it a focal point in climate science.
The Unique Nature of Thwaites Glacier
Thwaites Glacier is situated in Ellsworth Land, West Antarctica, and drains into the Amundsen Sea. It holds the distinction of being the widest glacier on Earth, spanning approximately 120 kilometers (75 miles) at its interface with the ocean. The glacier covers an expansive area of about 192,000 square kilometers (74,000 square miles), comparable in size to Florida or Great Britain.
Its grounding line, where ice transitions from bedrock to ocean, extends to significant depths, between 800 and 1,200 meters (2,600 and 3,940 feet) below sea level. The bedrock beneath much of Thwaites Glacier has a retrograde slope, meaning it deepens inland, making the glacier susceptible to instability once retreat begins. Combined with its immense size, this feature positions Thwaites as a natural “cork” stabilizing the broader West Antarctic Ice Sheet, slowing its movement into the ocean.
Observable Changes Over Time
Thwaites Glacier has undergone significant transformations, observed through satellite imagery. The glacier has been losing ice at an accelerated rate, contributing approximately 4% of global sea-level rise annually. Since 2000, the glacier has experienced a net loss exceeding 1,000 billion tons of ice, with the rate of ice flow nearly doubling in the past three decades.
The grounding line of Thwaites Glacier has retreated considerably, moving up to 14 kilometers inland since the late 1990s in some regions, with current retreat rates reaching up to 1.2 kilometers per year. The highest sustained rates of grounding zone retreat, up to 0.7 kilometers per year, are observed where ice-shelf channels intersect the grounding zone. This retreat is accompanied by ice sheet thinning, with some coastal areas thinning at approximately 3.2 meters per year in the 1990s.
The Thwaites Eastern Ice Shelf (TEIS) has shown significant breakup and fracturing. Since 2016, full-thickness rifts have episodically advanced throughout the central ice-shelf area, with rapid propagation events occurring during the austral spring. The ice shelf’s speed has increased by about 70% between 2019 and early 2023, transitioning from 1.65 meters per day to 2.85 meters per day in the central area. These observed changes, including new rifts and accelerated ice flow, indicate a weakening of the ice shelf’s buttressing effect.
Factors Driving Its Evolution
Rapid changes in Thwaites Glacier are primarily driven by several factors. A major contributor is the warming of ocean currents, specifically the Circumpolar Deep Water, which accesses the underside of the ice shelf. This warm, salty water, with a freezing point lower than freshwater, intrudes kilometers beneath the grounded ice, causing vigorous melting from below. Satellite radar data revealed that seawater flows in and out with the tides, and some of this warm water becomes trapped in cavities beneath the ice, further accelerating melting.
The glacier’s retrograde bed slope also plays a significant role. This geological configuration makes the glacier inherently unstable; once retreat of the grounding line begins, it can become a self-sustaining process, exposing more ice to warm ocean waters and accelerating melting. The retreat of the grounding line reduces friction at the glacier’s base, allowing the ice to flow more quickly into the ocean.
While less dominant than oceanic warming, geothermal heat flux, or heat from the Earth’s interior, may also contribute to basal melting. The region lies within the West Antarctic Rift System, and underlying geological processes, including potential subglacial volcanism, could increase basal geothermal heat flux. This melting, possibly supplemented by groundwater, can promote subglacial sediment erosion and transport, factors associated with enhanced ice flow.
Global Sea Level Implications
Changes at Thwaites Glacier hold considerable implications for global sea levels. The glacier alone contains enough ice to raise global sea levels by approximately 65 centimeters (25.6 inches) if it were to collapse entirely. This potential contribution is significant, considering that global sea levels have risen by about 20 centimeters since 1900.
Thwaites Glacier has earned the nickname “Doomsday Glacier” due to its potential to trigger substantial sea level rise. The concern stems from its collapse potentially destabilizing other parts of the West Antarctic Ice Sheet. As a natural buttress, Thwaites Glacier helps restrain the flow of neighboring glaciers. If it were to disintegrate, it could initiate a chain reaction, potentially adding several meters to global sea levels. Such an increase would have profound consequences for coastal communities worldwide, leading to increased tidal flooding, enhanced storm surges, and the inundation of low-lying areas.
Ongoing Scientific Investigations
Scientists are engaged in extensive research and international collaborations to understand Thwaites Glacier’s dynamics. A major undertaking is the International Thwaites Glacier Collaboration (ITGC), a partnership between the UK Natural Environment Research Council (NERC) and the US National Science Foundation (NSF). This joint project, launched in 2018, is the largest of its kind on the southern continent in 70 years, involving over 150 scientists and students from various countries.
The ITGC comprises several research projects, each focusing on different aspects of the glacier and its environment. For instance, the GHOST project gathers seismic and radar data on ice and bedrock, while the THOR project focuses on marine sediments, bathymetric mapping, and oceanography. Projects like MELT and TARSAN specifically investigate ice-ocean interactions, studying ocean circulation and rates of ice melt near the glacier front.
Scientists utilize advanced technologies, including high-resolution Worldview satellite imagery to create digital surface models, and instruments like CryoSat-2 and ICESat-2 for calibration and precise measurements of ice thickness and grounding line positions. This comprehensive research aims to improve predictions of future sea level rise and enhance the understanding of polar ice sheet dynamics.