[Homestead] Dynamics of global climate system

Tvoivozhd tvoivozd at infionline.net
Tue Sep 21 11:59:00 EDT 2004

University Of California - Santa Barbara <http://www.ucsb.edu/>

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    Past Antarctic Ice Sheet Development Linked To Ocean Temperatures
    And Carbon Dioxide

Santa Barbara, Calif.) –– New research published in the September 17 
issue of the journal Science sheds light on the evolution of Earth's 
climate system by identifying changes in temperature, ocean circulation, 
and global carbon cycling associated with the rapid growth of Antarctic 
ice sheets approximately 14 million years ago.

/View of East Antarctic Ice Sheet from Australia's Mawson Station. 
(Photo Credit: Katharine Burgdorff)/

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By studying chemical changes in deep sea sediments, scientists at the 
University of California, Santa Barbara discovered that high-latitude 
Southern Ocean cooling helped to trigger this major expansion of 
Antarctic ice sheets, which have since become a permanent feature of the 
global climate system. These results document ice sheet history and 
supply crucial insight into the dynamics of the global climate system.

Scientists have long recognized that the Southern Ocean and the 
development of Antarctic ice sheets play a major role in the evolution 
of Earth's present climate system. Only now have researchers been able 
to obtain a clearer picture of the relationship between high-latitude 
temperatures, global carbon cycling and the size of Antarctic ice sheets.

Southern Ocean temperature data exhibits a rapid 7 degree cooling of 
surface waters around 14 million years ago and suggests a strengthening 
of the Antarctic Circumpolar Current in response to changes in the 
geometry of Earth's orbits. As a result, Antarctica became increasingly 
isolated from tropical heat and moisture sources. Records of Antarctic 
ice volume indicate that following this cooling ice sheets expanded 
rapidly to near present-day size, which suggests that changes in the 
Southern Ocean directly influence the size of the Antarctic ice sheet.

UCSB researchers speculate that the climate system responded quickly to 
orbital variations because of generally low atmospheric carbon dioxide 
levels and plate tectonic changes north and south of Australia.

"Our study indicates that the sensitivity of Earth's climate system can 
shift rapidly when climate boundary conditions, such as atmospheric 
greenhouse gas levels or the configuration of the continents, change," 
said Amelia Shevenell, the lead author of the Science study and a Ph.D. 
candidate at UCSB.

"Our results suggest that scientifically it is somewhat incidental 
whether these boundary conditions are altered via natural or 
human-induced processes," she said. "If the boundary conditions change, 
we should expect Earth's climate system to respond."

Shevenell and co-authors Jim Kennett and David Lea, both professors of 
Geological Sciences at UCSB, developed the records of Southern Ocean sea 
surface temperature change, Antarctic ice volume, and global carbon 
cycling by measuring chemical changes in the fossilized skeletal remains 
of marine plankton contained in deep-sea sediments. Shevenell and 
Kennett collected these sediments south of Tasmania when they sailed as 
scientists on the Ocean Drilling Program's drill ship, the JOIDES 

This research was supported by the National Science Foundation and Joint 
Oceanographic Institutes.

*Editor's Note:* The original news release can be found here 

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