Antarctic ice sheet formed due to geological uplift from mantle waves

Antarctic ice sheet formed due to geological uplift from mantle waves

The origin of the East Antarctic Ice Sheet, the largest on Earth, has long been a puzzle for scientists. While the continent became covered in ice around 34 million years ago during the Eocene-Oligocene transition, the Arctic remained largely ice-free for another 25 million years. This disparity is surprising because falling carbon dioxide levels were driving global temperatures down at the time; if cooling were the only factor, both poles should have frozen simultaneously.

A new study published in Science, conducted by researchers in the UK and Germany, suggests the answer lies in deep geological forces. The research indicates that the land itself was pushed higher, creating the necessary conditions for ice to accumulate long before the Arctic experienced a similar freeze.

The Mechanics of Mantle Waves

The process began around 170 million years ago when Antarctica and Africa split apart as part of the supercontinent Gondwana. This rupture triggered "mantle waves" — swirling motions of hot material from Earth’s mantle that well up, cool, and sink. These waves can travel more than 1,000 kilometres through the sticky rock beneath a continent.

According to the research team, these mantle waves have several effects:

• They can trigger diamond-bearing volcanic eruptions, blasting magma from more than 150 kilometres below the surface.
• They generate pulses of land uplift far from the original rift zones.
• In East Antarctica, they created a coastal escarpment more than two kilometres high.

As the mantle wave migrated inland, it stripped away rock from deep beneath the continent. The land above lifted, similar to a hot air balloon rising after dropping ballast, creating a vast plateau. It took roughly 100 million years for this wave of uplift to reach the Gamburtsev mountains, located over 1,500km from the coast.

Crossing the Elevation Threshold

Elevation is critical for ice formation because air temperature drops by roughly 1°C for every 100 metres of elevation gained. Until approximately 50 million years ago, most of the Gamburtsev mountains were below 1.5km, an altitude where snow typically melted during the summer. However, models show the mantle wave pushed much of this range above 2km around 50 million years ago, allowing snow and ice to persist year-round.

By around 45 million years ago, enough of the landscape had crossed this threshold for mountain glaciers to take hold and spread. This coincided with a global temperature drop from around 30°C 50 million years ago to closer to 20°C.

Feedback Loops and Global Impact

Once the glaciers established themselves in the highlands, two positive feedback loops accelerated the process. First, the ice and snow reflected more sunlight than bare rock, which researchers suggest lowered global temperatures by around 1°C. Second, as the air cooled, it held less water vapour — a powerful greenhouse gas, reducing the insulating blanket over the region and allowing temperatures to drop further.

These combined forces allowed the ice to expand from the mountains down to the coast. This specific geological uplift explains why the Arctic did not freeze at the same time; northern landmasses lacked the necessary elevation to cross the threshold. It took another 25 million years and significantly lower CO₂ levels for Arctic ice sheets to form.

This theory also resolves a second mystery: why sea-surface temperatures in the Southern Ocean remained unexpectedly warm for roughly 10 million years after the ice sheet formed. The 1°C global cooling caused by the ice sheet was not enough to plummet the temperatures of the surrounding polar oceans.

Context of a Changing Continent

The current frozen state of Antarctica is a stark contrast to its ancient history. Fossil evidence, including "seed-fern" trees (Glossopteris) discovered near the Beardmore Glacier, proves the continent once supported tropical forests. Geological records show that 450 million years ago, the crust making up Antarctica actually straddled the equator.

Other tectonic events contributed to the deep freeze. The widening of the sea between Antarctica and Australia and the separation of the Antarctic Peninsula from South America roughly 35 million years ago helped establish the cold Circumpolar Current. This current prevents warm water from reaching the coast, further isolating the continent.

The research, supported in part by funding for Visiting Professor Thomas Gernon of the GFZ Helmholtz Centre for Geosciences, suggests that the conditions required to form a continental ice sheet are extraordinarily specific and take geological timescales to assemble. The researchers warn that while these sheets take millions of years to grow, they can disappear much faster when they melt and cannot simply grow back once lost.