Antarctica's ice sheet is the largest single mass of ice on the planet covering an area of almost 14 million square kilometers. It contains 30 million cubic kilometers of ice. The ice sheet contains about 90 percent of fresh water on Earth's surface.
Scientists already know a great deal about Antarctica but much about the oldest, coldest, driest and windiest continent in the world remains unknown particularly how it formed so rapidly about 34 million years ago.
Theories Explaining How Antarctica Formed
Two competing theories attempt to explain how the continent was formed. The first theory lies on the idea of a global climate change. The level of atmospheric carbon dioxide dropped steadily since the start of the Cenozoic Era 66 million years ago, and once the gas dropped below a critical threshold, the cooler temperatures allowed the formation of Antarctica's ice sheets.
The second theory, which is about the dramatic changes in ocean circulation patterns, posits that when the Drake Passage that lies between Antarctica and the southern tip of South America deepened dramatically, the phenomenon set off a complete reorganization of the ocean circulation.
The theory suggests that the increased separation of South America and the Antarctic land mass helped create the powerful Antarctic Circumpolar Current that served as a sort of water barrier which prevented the warmer waters from the Central Pacific and North Atlantic from going toward the Antarctic land mass. The isolation of Antarctica and the lowered temperature helped in the formation of ice sheets.
Combining The Two Theories
Now, a new study links these two theories. In the new paper published in Nature Geoscience, researchers argued that the changes in the Drake Passage led to a sort of domino effect. The warmer waters were initially pushed north which resulted in more rainfall about 35 million years ago since a warmer atmosphere can contain more moisture compared with a cooler one.
All the excess rain resulted in lowered carbon dioxide levels in the atmosphere which can be attributed to increased plant and tree growth, further made possible by a process known as silicate weathering, where carbon dioxide is trapped inside newly formed limestone. The levels of carbon dioxide eventually dropped low enough to allow the rapid formation of ice sheets in Antarctica.
"We suggest that this mechanism illustrates another way in which ocean-atmosphere climate dynamics can introduce nonlinear threshold behaviour through interaction with the geologic carbon cycle," wrote study researcher Galen Halverson, from McGill University's Dept. of Earth and Planetary Sciences, and colleagues in a study published online on Jan. 30.
The researchers think that they are the first to consider combining the two theories since the time scales of the ideas are vastly different. The changes in the ocean circulation occurred over a period of thousand years while global silicate weathering occurred over hundreds of thousands of years.
Antarctica And Climate Change
Scientists have been monitoring the Antarctic ice sheet as the melting ice can serve as indicator of a warming world. Late last year, scientists reported finding a lake of freshwater underneath the Roi Baudouin ice shelf in East Antarctica, which hints that climate change has impacted the region. The phenomenon raised concern about the broken masses of ice melting more easily in the sea.