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Algae helps explains Antarctic ice sheet formation

Antarctic ice sheets first began to form some 34 million years ago, during a period of sharply declining atmospheric carbon dioxide levels, a new study of ancient algae suggests.

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This photo, taken from NASA’s DC-8 research plane in October, shows a giant crack forming across Antarctica's Pine Island Glacier ice shelf. The ice shelf is in the midst of a natural process of calving a large iceberg, which it hasn’t done since 2001. Scientists say this type of cracking happens naturally every decade and is not related to global warming.

Jefferson Beck/Goddard Space Flight Center/NASA/AP

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Antarctica's vast ice sheets first grew when carbon dioxide levels in the Earth's atmosphere sharply declined millions of years ago, scientists now find.

Carbon dioxide is a greenhouse gas — it traps heat radiating away from the Earth's surface. High levels of it in the atmosphere are linked with global warming, while low levels are linked with global cooling. Many such periods of warming and cooling have occurred in the Earth's history, with repercussions for climate around the planet.

But reconstructions of what atmospheric carbon dioxide levels were like back when glaciers began to cover Antarctica nearly 34 million years ago had appeared contradictory. Some research actually suggested carbon dioxide levels rose just before and across this time, a period known as the Eocene-Oligocene climate transition, which is the opposite of what would be expected as prime glacier-growing conditions.

Now research suggests that a sharp decline of atmospheric carbon dioxide levels may have played a major role in seeding Antarctica's glaciers.

Ancient algae

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