With the exception of today's record levels, the atmospheric carbon dioxide concentration has been relatively stable over the past 2.1 million years, American researchers have found. A decline in CO2 concentration can not, as previously thought, have caused the great glacial periods during the Pleistocene geological age 1.2 million to 500, 000 years ago today. The results of Bärbel Hönisch of Columbia University in Palisades and her colleagues suggest that other factors must have caused the expansion of ice ages. Interesting side result of the study: Currently, the carbon dioxide levels are almost 40 percent higher than they were on average during the past two million years. Hönisch and her colleagues reconstructed the course of the atmospheric CO2 concentration over the past 2.1 million years and could find no indication that the atmospheric carbon dioxide concentration in the Pleistocene declined gradually about 850, 000 years ago. During this time, ice-time cycles stretched from 40, 000 to 100, 000 years, and many scientists blame cooling the atmosphere by reducing the concentration of CO2 for the onset of the great ice ages. However, the new results clearly showed that CO2 could be ruled out as a reason for the massive ice ages, the researchers report.
For the reconstruction, the scientists used fossilized plankton from the seabed on the coast of Africa. When plankton organisms petrify, the element boron that they have taken up during their lifetime is also trapped in the shell. This boron served researchers as a measure of the carbon dioxide content in the water. Because this Borvariante, also called isotope, prevails in the water, depends on the CO2 concentration of the water. The scientists thus determined which boron isotopes were found in the shells of the plankton and thus could indirectly infer the carbon dioxide concentration of the atmosphere.
The plankton organisms covered a period of up to 2.1 million years, allowing researchers to trace the course of carbon dioxide concentration further than was possible with previous measurements from polar ice drilling. With these methods, the values could be reconstructed only for about 800, 000 years, the transition to the great ice age in the Pleistocene, however, is about 850, 000 years back. The new results, as well as the previous studies, showed a close connection between the CO2 content in the atmosphere and the global climate? despite the lack of link between a decline in concentration and the intensification of ice ages.
Bärbel Hönisch (Columbia University, Palisades) et al .: Science, vol. 324, p. 1551 ddp / science.de? Stefanie shrub display