My OperaAntarctic Ice and Plate Tectonics
Tuesday, May 30, 2006 9:09:57 AM
Now that the Antarctic ice is melting away it may be relevant to ask why, how and when the Antartic ice was formed in the first place.
More than 30 million years ago rapid cooling seemed to have swept over Antartica replacing boreal pine forest with ice and snow, and by 33.6 million years ago Antarctica is known to have been covered with ice. This shows that the position on the South pole is only part of the story.
About 34 million years ago our planet underwent a so-called 'greenhouse to icehouse transition'. Earth went from having virtually no ice on it at all to one with a more or less permanent ice sheet covering Antartica.
The Antarctic ice sheet may have been initiated by a drop in greenhouse gas concentration in combination with a change in ocean circulation.
Today the Antarctic Circumpolar Current (ACC) is the most important current in the Southern Ocean, and the only current that flows completely around the globe. The ACC transports more water than any other ocean current. It extends from the sea surface to depths of 2000-4000 m and can be as wide as 2000 km. This cold current (shown in blue) isolates Antartica from any warm (red) current transporting heat southwards.
This has nor always been the case. Sometimes all continents were united in one big supercontinent. One such supercontinent was Gondwana. 200 million years ago Antarctica was near the equator and surrounded on three sides by Australia, India, Africa, and South America. About 160 million years ago the supercontinent Gondwana began to break apart in bits and pieces that slowly drifted towards their present locations around the world.
50 million years ago Antarctica was not yet separated from South America and Australia, and the warm currents (shown in red) could still reach the coasts of Antarctica. When the seaways between Antarctica and respectively South America and Australia opened deep enough to allow the Antarctic Circumpolar Current to pass around Antarctica has been somewhat controversial.
Drilling cores from The Ocean Drilling Program (ODP) indicated that the Tasmanian Gateway opened between 37 and 33.5 million years ago. The fact that estimates of the age of the Drake Passage ranged from 49 millions to 17 million years ago complicated interpretations of the relationship between ocean circulation and global cooling. If the opening of the Drake Passage took place much later than the opening of the Tasmanian Gareway, then the Antarctic Circumpolar Current has nothing to do with the sudden cooling of Antarctica about 34 million years ago.
Findings from a study reported in the journal Science of 21 April 2006 and based on Nd (neodynium) isotopes in fish teeth found downstream from the drake Passage indicate however that the pasage must have begun to open 41 million years ago. This report therefore concludes that yhe opening of the drake Passage preceded the opening of the last remaining corridor, the Tasmanian gateway, around 35 million years ago, and major ice sheets growth in Antarctica, which began around 34 million years ago.
Sources and relevant links:
Timing and Climatic Consequences of the Opening of Drake Passage by Howie D. Scher and Ellen E. Martin (Science, 21 April 2006, VOL 312, pp. 428-430)
Paleogene opening of Drake Passage by Roy Livermore, Adrian Nankivell, Graeme Eagles and Peter Morris (Earth and Planetary Science Letters 236 (2005) 459– 470)
More than 30 million years ago rapid cooling seemed to have swept over Antartica replacing boreal pine forest with ice and snow, and by 33.6 million years ago Antarctica is known to have been covered with ice. This shows that the position on the South pole is only part of the story.
About 34 million years ago our planet underwent a so-called 'greenhouse to icehouse transition'. Earth went from having virtually no ice on it at all to one with a more or less permanent ice sheet covering Antartica.
The Antarctic ice sheet may have been initiated by a drop in greenhouse gas concentration in combination with a change in ocean circulation.
Today the Antarctic Circumpolar Current (ACC) is the most important current in the Southern Ocean, and the only current that flows completely around the globe. The ACC transports more water than any other ocean current. It extends from the sea surface to depths of 2000-4000 m and can be as wide as 2000 km. This cold current (shown in blue) isolates Antartica from any warm (red) current transporting heat southwards.
This has nor always been the case. Sometimes all continents were united in one big supercontinent. One such supercontinent was Gondwana. 200 million years ago Antarctica was near the equator and surrounded on three sides by Australia, India, Africa, and South America. About 160 million years ago the supercontinent Gondwana began to break apart in bits and pieces that slowly drifted towards their present locations around the world.
50 million years ago Antarctica was not yet separated from South America and Australia, and the warm currents (shown in red) could still reach the coasts of Antarctica. When the seaways between Antarctica and respectively South America and Australia opened deep enough to allow the Antarctic Circumpolar Current to pass around Antarctica has been somewhat controversial. Drilling cores from The Ocean Drilling Program (ODP) indicated that the Tasmanian Gateway opened between 37 and 33.5 million years ago. The fact that estimates of the age of the Drake Passage ranged from 49 millions to 17 million years ago complicated interpretations of the relationship between ocean circulation and global cooling. If the opening of the Drake Passage took place much later than the opening of the Tasmanian Gareway, then the Antarctic Circumpolar Current has nothing to do with the sudden cooling of Antarctica about 34 million years ago.
Findings from a study reported in the journal Science of 21 April 2006 and based on Nd (neodynium) isotopes in fish teeth found downstream from the drake Passage indicate however that the pasage must have begun to open 41 million years ago. This report therefore concludes that yhe opening of the drake Passage preceded the opening of the last remaining corridor, the Tasmanian gateway, around 35 million years ago, and major ice sheets growth in Antarctica, which began around 34 million years ago.
Sources and relevant links:
Timing and Climatic Consequences of the Opening of Drake Passage by Howie D. Scher and Ellen E. Martin (Science, 21 April 2006, VOL 312, pp. 428-430)
Paleogene opening of Drake Passage by Roy Livermore, Adrian Nankivell, Graeme Eagles and Peter Morris (Earth and Planetary Science Letters 236 (2005) 459– 470)
- Antarctica in the past http://www.secretsoftheice.org/explore/past.html with plate tectonic animation
- The Antarctic CP Current http://oceancurrents.rsmas.miami.edu/southern/antarctic-cp.html
- Opening Of Passage May Be Tied To Antarctic Cooling http://www.terradaily.com/reports/Opening_Of_Passage_May_Be_Tied_To_Antarctic_Cooling.html
- Ocean currents helped frost Antarctica http://feeds.asiapacificnews.net/?rid=8b8244203d6aac5d&cat=4a8b544d0e80ba53&f=1
- New Evidence of Early Glacial Development, History of Antarctic Ice Sheet Revised http://www.physorg.com/news66060296.html
- opening of the Tasmanian Gateway http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_65573.htm
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