Today.Az » Weird / Interesting » Prehistoric greenhouse data from ocean floor could predict earth's future, study finds
01 November 2011 [09:30] - Today.Az
New research from the University of Missouri indicates that Atlantic Ocean temperatures during the greenhouse climate of the Late Cretaceous Epoch were influenced by circulation in the deep ocean. These changes in circulation patterns 70 million years ago could help scientists understand the consequences of modern increases in greenhouse gases.
"We are examining ocean conditions from several past greenhouse
climate intervals so that we can understand better the interactions
among the atmosphere, the oceans, the biosphere, and climate," said
Kenneth MacLeod, professor of geological sciences in the College of Arts
and Science. "The Late Cretaceous Epoch is a textbook example of a
greenhouse climate on earth, and we have evidence that a northern water
mass expanded southwards while the climate was cooling. At the same
time, a warm, salty water mass that had been present throughout the
greenhouse interval disappeared from the tropical Atlantic."
The study found that at the end of the Late Cretaceous greenhouse
interval, water sinking around Greenland was replaced by surface water
flowing north from the South Atlantic. This change caused the North
Atlantic to warm while the rest of the globe cooled. The change started
about five million years before the asteroid impact that ended the
Cretaceous Period.
To track circulation patterns, the researchers focused on
"neodymium," an element that is taken up by fish teeth and bones when a
fish dies and falls to the ocean floor. MacLeod said the ratio of two
isotopes of neodymium acts as a natural tracking system for water
masses. In the area where a water mass forms, the water takes on a
neodymium ratio like that in rocks on nearby land. As the water moves
through the ocean, though, that ratio changes little. Because the fish
take up the neodymium from water at the seafloor, the ratio in the fish
fossils reflects the values in the area where the water sank into the
deep ocean. Looking at changes through time and at many sites allowed
the scientists to track water mass movements.
While high atmospheric levels of carbon dioxide caused Late
Cretaceous warmth, MacLeod notes that ocean circulation influenced how
that warmth was distributed around the globe. Further, ocean circulation
patterns changed significantly as the climate warmed and cooled.
"Understanding the degree to which climate influences circulation and
vice versa is important today because carbon dioxide levels are rapidly
approaching levels most recently seen during ancient greenhouse times,"
said MacLeod. "In just a few decades, humans are causing changes in the
composition of the atmosphere that are as large as the changes that
took millions of years to occur during geological climate cycles."
The paper, "Changes in North Atlantic circulation at the end of the
Cretaceous greenhouse interval," was published in the October online
edition of the journal Nature Geoscience. Coauthors include C.
Isaza Londoño of the University of Missouri; E.E. Martin and C. Basak of
the University of Florida, and A. Jiménez Berrocoso of the Unviersity
of Manchester, United Kingdom. The study was sponsored by the National
Science Foundation.
/Science Daily/
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