How did Antarctica turned into a frigid place
The first theory is that atmospheric carbon dioxide levels steadily declined after the Cenozoic Era about 66 million years ago. Once it was below a certain threshold, ice sheets began to form, creating Antarctica.
The second is it could be a result of changes to the Drake Passage — the body of water between South America and Antarctica — which deepened about 35 million years ago and triggered a dramatic shift in ocean currents. The increasing separation between Antarctica and South America created a powerful underwater tug called the Antarctic Circumpolar Current (ACC). The ACC blocked warmer waters from the North Atlantic and Central Pacific from moving towards Antarctica, isolating it and allowing ice sheets to form.
In their new paper, the researchers, led by scientists in McGill University's Department of Earth and Planetary Sciences, argue that the changes in the Drake Passage resulted in a sort of domino effect: First, warmer water was pushed north, which led to more rainfall about 35 million years ago, because a warmer atmosphere can hold more moisture than a cooler one before reaching saturation, and when it does cool down, this moisture condenses to liquid and it rains.All that extra rain, in turn, lowered the carbon dioxide levels in the atmosphere by increasing plant and tree growth and via a process called silicate weathering, where carbon dioxide gets trapped inside newly-formed limestone.
Eventually, carbon dioxide levels dropped low enough for ice sheets to start forming rapidly in Antarctica.
The team believe they are the first to think of combining these two theories because the time scales of the ideas are vastly different; changes in ocean circulation happen over thousands of years, whereas global silicate weathering happens over hundreds of thousands of years.
"It's an interesting lesson for us when it comes to climate change," Dr Galen Halverson, professor of Earth and Atmospheric Science at McGill University and one of the authors of the paper, said in a statement. "Because what we get is a thumbnail shift between two stable climatic states in Antarctica — from no glaciers to glaciers. And what we see is both how complex climate changes can be and how profound an effect changing patterns of ocean circulation can have on global climate states, if looked at on a geological time scale."