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Greenland ice core dating

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"The Mid Pleistocene Transition is a most important and enigmatic time interval in the more recent climate history of our planet," says Fischer.

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“The idea that there was a lag of CO2 behind temperature is something climate change skeptics pick on,” says Edward Brook of Oregon State University’s College of Earth, Ocean and Atmospheric Sciences.Now, an international team of scientists wants to know what happened before that.At the root of their quest is a climate transition that marine-sediment studies reveal happened some 1.2 million years to 900,000 years ago.“They say, ‘How could CO2 levels affect global temperature when you are telling me the temperature changed first?’” Frédéric Parrenin of the Laboratory of Glaciology and Geophysical Environment in France and a team of researchers may have found an answer to the question.Ice cores provide excellent seasonal markers allowing very accurate dating.

Seasonal markers such as stable isotope ratios of water vary depending on temperature and can reveal warmer and colder periods of the year.

Through analysis of ice cores, scientists learn about glacial-interglacial cycles, changing atmospheric carbon dioxide levels, and climate stability over the last 10,000 years. This picture shows a traversing field camp from December 2010.

From top to bottom: * Levels of carbon dioxide (CO2). High rates of snow accumulation provide excellent time resolution, and bubbles in the ice core preserve actual samples of the world’s ancient atmosphere[6].

There is, however, still a degree of uncertainty about which came first—a spike in temperature or CO2.

Until now, the most comprehensive records to date on a major change in Earth’s climate came from the EPICA Dome C ice core on the Antarctic Plateau.

By studying the past climate, scientists can understand better how temperature responds to changes in greenhouse-gas concentrations in the atmosphere.