Rising Antarctica: Melting Glaciers and Continental Uplift

Most of us have heard the story of Archimedes, the brilliant Greek thinker who, upon stepping into a bathhouse, noticed the water level rise, deduced the principles of buoyancy responsible for the rise, and famously rushed to share his discovery with the world, running naked through the streets and shouting "Eureka!" (εὕρηκα; "I have found it" in Greek). Although this tale is likely more legend than fact, the principles it illustrates are foundational to our understanding of buoyancy. Archimedes realized that buoyancy is essentially the balance between two forces: gravity, which pulls a body downward toward Earth’s center, and the buoyant force, which a liquid exerts upward on the submerged object. Gravity depends on the object's mass, while the buoyant force is determined by the volume of liquid the object displaces.

These same principles of buoyancy also apply, on a much larger scale, to the buoyancy of continents.  Although continents appear stable and stationary, they actually "float" on the viscous layer of Earth's upper mantle (also known as the asthenosphere). Buoyancy, therefore, or, more precisely, the balance of forces, depends on the mass and volume of the continents. It can be inferred, therefore, that glacier melting on Earth's surface will lead to changes in this mass, raising an intriguing question: what happens when the mass of a continent changes? 

A recent study, published in Science in August, investigates the future of Earth's sea levels by introducing a previously overlooked factor: changes in the buoyancy of Antarctica. As Antarctica’s mass decreases, the continent is expected to rise gradually—at varying rates in different regions. This land uplift, in turn, is expected to influence both the pace and direction of sea level changes worldwide.

A-B: Sea level in 2150 and 2500 under a moderate warming model; E-F: Sea level under a rapid warming model. Projections of ocean level changes due to Antarctic ice loss | From Gomez et al.

The Glaciers Descend, the Waters Rise

Adding mass to a body causes it to sink deeper into water as it balances gravitational and buoyant forces. This principle is easy to observe in cargo ships, which sit lower in the water when heavily loaded and rise higher when unloaded.  Similarly, we "sail" on continents that, as previously noted, float atop the viscous material of Earth's mantle. The accumulation of heavy glaciers on a continent causes it to sink deeper into the mantle, much like a heavily loaded ship sinks into the sea, until the buoyant force counterbalances the added weight. In recent years, glacier melting has reduced this mass, causing Antarctica to rise—a process known as ‘post-glacial rebound,’ which has wide-ranging and complex implications for Earth."With nearly 700 million people living in coastal areas and the potential cost of sea-level rise reaching trillions of dollars by the end of the century, understanding the domino effect of Antarctic ice melt is crucial,” said glaciologist Natalia Gomez, who led the study, in an interview with ScienceAlert.

The researchers examined the relationship between continental uplift (post-glacial rebound) and melting glaciers, taking into account the properties of the Earth's mantle, which, as mentioned, can influence the degree of buoyancy. The study’s findings reveal that Earth’s mantle viscosity, which varies beneath the Antarctic continent, affects the rate of its uplift. For example, in regions where the mantle is more viscous, the model predicts an exceptionally rapid uplift, occurring over decades rather than over the millennia usually assumed in modeling studies of the  Antarctic region. 

Using collected data, the researchers constructed 3D models simulating sea-level rise following changes in the continent's mass. Each model defined different conditions, in order to assess the potential outcomes of various scenarios. In low-end projections, Antarctic ice loss is estimated to contribute about 1.7 meters to sea-level rise by the year 2500. In this scenario, the uplift of Antarctica could partially offset sea-level rise. The rising continent would push some of the ice away from the water, delaying contact between the ice and the relatively warm ocean water, which accelerates melting. This process could slow the melting, allowing more ice to remain frozen for longer. On the other hand, in high-end projections,glacier melting and ice retreat would outpace the rate of continental uplift, leading to a sea-level rise of approximately 19.5 meters - more than ten times greater than the low-end estimate. In this case, the effect of continental uplift would be negligible.

At high risk of flooding due to rising sea levels. Kiritimati (also known as Christmas Island), located in the Republic of Kiribati in the central Pacific Ocean | A mosaic of images from the International Space Station provided by the Earth Sciences and Image Analysis Laboratory at Johnson Space Center.

The Rise is Already Here

Since planet Earth is not a perfect sphere, different regions will be affected differently by changes. Factors such as location, gravitational effects, land structure, and the properties of the viscous mantle all play a role in how different parts of the planet will respond. For instance, the equatorial region is expected to experience higher-than-average sea-level rise due to its geographical position. According to data collected by NASA, countries in this region are already grappling with the impact of rising sea levels. Over the past 30 years, sea levels along the coasts of Kiribati, a Pacific island nation, have risen by approximately 5 to 11 centimeters. On Tarawa, the island that houses the nation’s capital and has a maximum elevation of only three meters above sea level, residents are facing increasingly frequent coastal flooding. As a precaution, the country’s former president purchased land in Fiji to serve as a potential refuge for "climate refugees" (individuals displaced due to climate change), should the need arise. A similar threat looms for other Pacific island nations, such as Tuvalu, the Marshall Islands, and the Maldives. These equatorial regions are particularly vulnerable to coastal flooding, which occurs as a consequence of melting of polar ice caps, creating what some might call a "geological injustice."

“This study marks a breakthrough in our ability to better predict the impacts of climate change on rising seas and to inform effective environmental policy,” said glaciologist Rob DeConto, a co-author of the study. However, the researchers caution that their model does not incorporate all relevant data due to a lack of information about the mantle in West Antarctica, limiting its conclusions. Additionally, the model does not account for melting glaciers in Greenland or in high mountain ranges worldwide. Improving such models will enable us to better prepare for the anticipated impacts of climate change.