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The vast white expanse of Antarctica may hold a surprising secret: its eastern and western regions didn’t freeze over at the same time. A new study has suggested a gap of millions of years between the two, potentially explaining why West Antarctica is more vulnerable to modern-day warming.
According to the research, published in the journal Science, permanent ice sheets first locked down Eastern Antarctica a staggering 34 million years ago. It wasn’t until 7 million years later that ice sheets reached Western Antarctica, a region now experiencing concerning rates of meltwater loss.
This timeline aligns with a critical shift in Earth’s climate, roughly 34 million years back. The planet transitioned from a greenhouse world to an icehouse one, a dramatic change that initiated the growth of the massive Antarctic ice sheet. This sheet, in turn, has profoundly shaped global climate ever since.
“We so far didn’t know where and how much ice existed in Antarctica just after the transition from the Eocene greenhouse climate to the icehouse climate that prevails until today,” Johann Klages, Senior Marine Geologist at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, told Down To Earth.
Klages and his colleagues examined sediment samples from drill cores from a seafloor drill rig located offshore the Pine Island and Thwaites glaciers on the Amundsen Sea coast of West Antarctica. They then combined this with advanced climate and ice-sheet modelling.
The samples showed no evidence of ice presence in this region during the first major phase of Antarctic glaciation, which occurred approximately 34 million years ago.
“This means that a large-scale, permanent first glaciation must have begun somewhere in East Antarctica,” Klages explained in a statement.
This, he added, is because West Antarctica may have been home to dense broadleaf forests during that period. A cool-temperate climate likely prevented ice from forming in the region.
The ice advance to the Amundsen Sea sector in Western Antarctica was most likely slowed by the mild air and surface ocean temperatures. The movement towards the Ross Sea sector started earlier.
Climate modelling simulations revealed that the coastal regions of the East Antarctic Northern Victoria Land had climatic conditions conducive to the formation of permanent ice.
The Transantarctic Mountains, which now separate East and West Antarctica, encountered moist air masses, allowing permanent snow and ice caps to form.
Then, the ice sheet spread rapidly into the East Antarctic hinterland. And when conditions became favourable 7 million years later, it began its march towards West Antarctica.
Klages explained that bringing grounded ice towards the West Antarctic coast took more effort when compared to its Western counterpart as many parts of West Antarctica were already situated below sea level.
“Our results clearly show how cold it had to get before the ice could advance to cover West Antarctica that, at that time, was already below sea level in many parts,” Hanna Knahl, a paleoclimate modeller at the Alfred Wegener Institute, said in a statement.
Many areas in West Antarctica, Klages explained, are below sea level today. This means we would need a lot less effort to let the West Antarctic ice sheet disappear when compared to its East Antarctic companion. A slight warming is enough to cause the ice in West Antarctica to melt again, which is already happening.
The new findings, according to the researchers, can help improve current climate models’ predictive capabilities.
