Scientists have identified a geological explanation for why Antarctica developed a permanent ice sheet millions of years before large ice sheets formed in the Northern Hemisphere.
International research published in Science addresses the long-standing climate mystery of how East Antarctica became covered by a massive ice sheet when global temperatures were about 5°C warmer than today.
The study suggests that highlands in East Antarctica gradually rose over millions of years. The uplift of coastal cliffs, plateaus, and mountain ranges created elevations cold enough for snow and ice to survive year-round, eventually allowing glaciers to accumulate and form the East Antarctic Ice Sheet.
This geological transformation began after Antarctica and Africa started separating during the Jurassic Period, approximately 201 million to 143 million years ago. Powerful forces deep within Earth gradually raised much of East Antarctica over a period of more than 100 million years, preparing the landscape for ice sheet formation around 34 million years ago.
The research was led by scientists from the University of Southampton, in collaboration with researchers from Durham University, Germany’s GFZ Helmholtz Centre for Geosciences, the University of Potsdam, Utrecht University in the Netherlands, and the University of Florence in Italy.
Lead author Thomas Garnon, professor of geosciences at the University of Southampton, said: “Despite the surrounding polar oceans and global temperatures remaining surprisingly warm, the Antarctic surface gradually rose to the point where ice could establish a permanent foothold.”
The East Antarctic Ice Sheet is currently the largest ice sheet on Earth. If it melted completely, the frozen water it contains could raise global sea levels by approximately 52 meters.
Computer models simulate 100 million years of Antarctic uplift
To reconstruct how East Antarctica’s landscape changed, the researchers used computer models to simulate the evolution of the region’s surface over the past 100 million years.
The results indicate that a geological phenomenon known as “mantle waves” caused much of the region’s gradual uplift.
Professor Garnon’s team recently identified mantle waves, which move beneath continents after tectonic plates begin to separate. These slow-moving waves have previously been linked to volcanic eruptions, including those associated with the Diamond Volcano, as well as periods of unexplained uplift within continents.
As mantle waves moved beneath East Antarctica, they helped raise a vast plateau topped by the Gamburtsev Mountains. This newly identified geological mechanism may explain how the continent reached the elevations required for permanent snow and ice to develop.
Computer simulations show that by approximately 45 million years ago, large areas of East Antarctica had risen above the critical elevation of about 2 kilometers needed for mountain glaciers to form and expand. Over time, these glaciers grew into the East Antarctic Ice Sheet.
Dr. Thea Hincks, a senior research fellow at the University of Southampton and co-leader of the study, said: “We show that our model realistically captures the evolution of two-kilometer-high coastal cliffs, raised plateaus, and inland mountains, which could ultimately seed the East Antarctic Ice Sheet.”
Why did Antarctica freeze before the Arctic?
The findings may also explain why Antarctica and the Arctic followed such different paths during Earth’s climate history.
Antarctica became heavily glaciated approximately 34 million years ago, while large ice sheets in the Northern Hemisphere did not form until about 5 million years ago.
Declining atmospheric carbon dioxide (CO2) levels are widely considered an important trigger of the Antarctic ice age. However, the first Antarctic ice sheets began forming while Earth’s climate was still relatively warm.
Professor Garnon explained: “If declining CO2 levels acted alone, the two poles would be expected to respond more symmetrically. Instead, Antarctica gained a significant head start because geological processes lifted the land to higher elevations, making it colder.”
How the Gamburtsev Mountains helped Antarctic ice survive
Even gradual changes in mountain elevation can determine whether snow melts during summer or remains long enough to accumulate from one year to the next.
Until approximately 50 million years ago, most of the Gamburtsev Mountains stood less than 1.5 kilometers above sea level. By about 34 million years ago, nearly half of the mountain range had risen above 2 kilometers. These high elevations were cold enough for snow and ice to persist throughout the year and gradually develop into ice caps.
Dr. Guy Paxman, a Royal Society Research Fellow at Durham University and co-author of the study, said: “Topography is fundamentally important for ice ages. Temperatures can fall by up to 1°C for every 100 meters of elevation.”
As the Antarctic ice sheet expanded, additional climate feedback mechanisms intensified regional and global cooling.
Dr. Philip Goodwin, a climate physicist at the University of Southampton and co-author of the study, said: “As the ice sheet expanded, its bright surface reflected more sunlight back into space, cooling the region further.”
Researchers estimate that this process, known as the ice-albedo effect, reduced global temperatures by approximately 1°C. However, this additional cooling was not enough to create large ice sheets in the Northern Hemisphere. Much of the Arctic region consists of relatively low-lying land, providing fewer elevated areas where permanent ice could form.
Cooling feedbacks helped ice spread across Antarctica
As Antarctica cooled, other feedback mechanisms strengthened the temperature decline. Colder air holds less water vapor, while water vapor normally acts as an insulating blanket around Earth. As the atmosphere became drier, this insulating effect weakened, causing temperatures to fall even further.
“These feedbacks allowed the Antarctic ice sheet to spread from the mountains across the continent and eventually reach the coast,” Dr. Goodwin added.
The discovery could change how scientists understand the origins of major ice ages. Climate conditions may not be the only factor determining when ice sheets form. Geological forces deep within Earth may first need to raise the landscape to elevations where permanent ice can survive.
“Our findings reveal that Earth’s interior helps create the topography required for ice ages and influences when and where major climate changes, such as the Antarctic Ice Age, can occur,” Professor Garnon said. “This is critical for understanding ancient ice ages and future climate tipping points.”
The research was supported by the WoodNext Foundation, a donor-advised endowment program.
Source: www.sciencedaily.com