Why Antarctica went into deep freeze 34 million years ago
Friday, 29 Feb 2008 14:23
The oceans did cool 34 million years ago, study finds
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Scientists believe they may have solved some of the mystery surrounding the creation of the Antarctic ice sheet 34 million years ago.
Temperature records have shown no evidence of the oceans cooling during this time and instead suggest that they warmed.
Now a team of scientists from Cardiff University and the National Museum Wales say their studies of ancient sea floor mud have contradicted these records and paint a less confusing period of the climate system that led to the Antarctic ice sheet.
Their studies of the mud, recovered from Tanzania, and the shell chemistry of pin-head sized animals called 'forams' found in it show that ocean temperatures did in fact cool by about 2.5C.
The chemistry of the Tanzanian microfossils enabled the scientists to construct records of temperature and ice volume over the climate period 34 million years ago.
These records show that the oceans cooled, creating enough ice to fit onto Antarctica.
"Forams are great tools for studying climates of the past, which helps us learn about the uncertainties of our future greenhouse climate," said Dr Carrie Lear.
"These new records help resolve a long-standing puzzle regarding the extent of ice-sheet growth versus global cooling, and bring climate proxy records into line with climate model simulations."
The researchers now plan to use forams to study the cause of the global cooling.
At present they believe the main cause is a gradual reduction of carbon dioxide in the atmosphere, combined with a 'trigger' time when Earth's orbit around the sun made Antarctic summers cold enough for ice to remain frozen all year round.
