Scientists have uncovered why Antarctica became engulfed by ice millions of years before the Arctic.
The international research, published today in Science , helps to solve one of climate science's longest-standing puzzles: how a vast ice sheet could form when Earth was around 5ºC warmer than today.
The study shows that the formation of an escarpment, plateau, and mountain region in East Antarctica created the high ground needed for snow and ice to accumulate.
Triggered when Antarctica and Africa began to break apart during the Jurassic Period 201-143 million years ago, powerful processes deep within the Earth drove much of East Antarctica's land surface to be uplifted over 100 million years, initiating ice sheet formation 34 million years ago.
Scientists at the University of Southampton led the study, working with colleagues at Durham University, GFZ Helmholtz Centre for Geosciences in Germany, the University of Potsdam in Germany, Utrecht University in the Netherlands, and the University of Florence in Italy.
Lead author Thomas Gernon, Professor of Earth Science at the University of Southampton, explained: "Antarctica's land surface was gradually lifted to the point where ice could gain a permanent foothold, even while the surrounding polar oceans as well as global temperatures remained surprisingly warm."
The East Antarctic Ice Sheet is the largest on Earth, storing enough frozen water to raise global sea levels by around 52 metres if it were to melt completely.
Retracing landscape change through simulations
The researchers used computational models to reconstruct how East Antarctica's surface evolved over 100 million years.
They found that 'mantle waves' explain how the surface of East Antarctica gradually rose.
Mantle waves are a recently discovered phenomenon by Prof Gernon's team. They spread under continents when tectonic plates break apart and have been shown to cause the eruption of diamond volcanoes and mysterious phases of uplift within continents .
When these slow-moving waves moved under East Antarctica, they formed a vast high plateau crowned by the Gamburtsev Mountains. It is the recent discovery of mantle waves that allowed the team to solve the mystery of why Antarctica froze.
The team's simulations revealed that by about 45 million years ago, much of the East Antarctic landscape had risen above the critical elevation – about 2 km – needed for mountain glaciers to form and expand, eventually merging into the East Antarctic Ice Sheet.
Dr Thea Hincks, Senior Research Fellow at the University of Southampton who co-led the study, said: "We found that our models can realistically capture the evolution of the two kilometre-high coastal escarpment, elevated plateau and inland mountains, eventually seeding the East Antarctic Ice Sheet."
The research helps to explain the striking asymmetry in polar ice in the past. Antarctica became glaciated about 34 million years ago, but large Northern Hemisphere ice sheets did not assemble until approximately the past five million years.
While declining levels of carbon dioxide (CO2) in the atmosphere is widely seen as the trigger for Antarctic glaciation, the first ice sheets began to form when the climate was still relatively mild.
Prof Gernon explained: "If falling levels of CO2 acted alone, you would expect the poles to respond more symmetrically. Instead, Antarctica gained a major head start because geological processes had raised land to higher elevations, making it colder."
The mountains' role
Small rises in the height of a mountain range can be the difference between snow melting in summer or surviving and accumulating year-on-year.
Before 50 million years ago, most of the Gamburtsev Mountains lay below 1.5 km in elevation. But by 34 million years ago almost half of the range stood above 2 km – high enough for snow and ice to persist year-round until it has built up into an ice cap.
Dr Guy Paxman, Royal Society University Research Fellow at Durham University and study co-author, explained: "Topography is fundamentally important for glaciation. Air temperatures can drop by up to 1ºC for every 100 metres of altitude gained."
Dr Philip Goodwin, climate physicist at the University of Southampton and study co-author, added: "As the ice sheet expanded, its bright surface reflected more sunlight back into space, cooling the region further."
The team estimates that this feedback, called the 'ice-albedo effect', lowered global temperatures by about 1ºC. But that was not enough for ice sheets to form in the Northern Hemisphere and so the landmasses in the Arctic region remained largely ice-free due to their lower elevations.
Once Antarctic cooling started, it triggered a further climate feedback: colder air holds less water vapour, which usually wraps the Earth like a warm blanket. As the air dried, this insulating effect weakened, allowing temperatures to fall further still.
"Together, these feedbacks allowed the Antarctic ice sheet to spread from the mountains across the continent, eventually reaching the coast," added Dr Goodwin.
The study may change how we think about the origins of ice ages.
"Our findings reveal that the Earth's interior preconditions landscapes to glaciation, determining when and where major climate transitions like the glaciation of Antarctica become possible," explained Prof Gernon. "That's incredibly important for understanding Earth's ancient ice ages as well as future tipping points in the climate system."
The research was made possible by the support of the WoodNext Foundation , a fund of a donor-advised fund program.
