Arctic ice formed much earlier than previous estimates: study
Prehistoric geological records from the frigid vault of the Arctic Ocean have shown that glaciers were formed in the Arctic Ocean about 45 million years ago, 14 million years earlier than geologists had thought, scientists reported on Wednesday.
The evidence, pea-sized pebbles locked inside a 430 meter-long sediment core, also indicates that the immense sheets of ice at the Earth's two poles formed almost simultaneously. Earlier, geologists had believed that glaciers had formed in Antarctica long before they appeared in the Arctic.
These findings appeared in three papers in the June 1 issue of the journal Nature.
The new study clears up the climate mystery and underscores the role that carbon dioxide and other greenhouse gases play in climate change, according to researchers from the Arctic Coring Expedition (ACEX), an international research project which recovers and analyzes ice core evidence from under the Arctic Ocean.
The retrieved evidence provides a 56-million-year climate record spanning the transition from a warm "greenhouse" to a colder "icehouse" world, and identifies more key events in the history of the Arctic Ocean, according to the researchers.
About 55 million years ago, they said, the surface water of the ocean was much warmer than previous estimates, and at one time Arctic temperatures rose to about 23 degrees Celsius, as high as today's subtropical level.
At one point 49 million years ago, the Arctic was green, with fresh surface water and large amounts of fern covering the water at least in summer months, the researchers said. The first ice-rafted debris occurred 45 million years ago.
"The revised timing of the earliest Arctic cooling events coincides with those from Antarctica, supporting arguments for bipolar symmetry in climate change," the researchers wrote in one paper.
The evidence also sheds new light on the global warming theory, which says human-induced greenhouse gases have warmed the Earth to record-high levels. The findings from this study indicate that 45 million years ago, the Earth's greenhouse gas levels could haven been much higher than today.
"This suggests that higher-than-modern greenhouse gas concentrations must have operated in conjunction with other feedback mechanisms-perhaps polar stratospheric clouds or hurricane-induced ocean mixing-to amplify early Palaeogene polar temperatures," they wrote in the Nature paper.
|People's Daily Online --- http://english.people.com.cn/|