Oxygen isotope level
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Oxygen isotope stage also marine isotope stage ( MIS ) or isotope stage is in geology the dating of sediment layers based on the stable isotopes of oxygen they contain . At colder temperatures, a higher proportion of 18 O was built into the skeletons of fossil foraminifera . Therefore, the ratio of 18 O to 16 O in the calcite on the ocean floor varies depending on the warm or cold period . In this way, the course of the Quaternary climate can be reconstructed. Similar studies exist for the entire Cenozoic era .
principle
The reduced ocean temperatures during the cold periods also have a local effect on the isotope ratio of the calcareous shell of the foraminifera, because when the calcium carbonate is incorporated into its housing, the foraminifera fractionates the 18 O / 16 O ratio at lower temperatures to the heavier isotope ( temperature effect ). An increased evaporation in the habitat of the foraminifera, but also an increased input of isotopically lighter melt water leads to a shift of the 16 O / 18 O ratio in the water and thus in the shell of the calcareous algae ( salinity effect ). Due to the fact that the ice effect has the greatest influence and the temperature effect shifts the 16 O / 18 O ratio in the same direction, a stratigraphy for marine sediments , the marine oxygen isotope stratigraphy , can be developed from this . The normalized ratio of 16 O / 18 O is referred to as δ 18 O or also Delta-O-18.
The first systematic investigations into the variation of oxygen isotopes in ocean sediments were carried out by Cesare Emiliani in the 1950s on planktonic foraminifera in drill cores from the Caribbean deep sea. He noticed the cyclical fluctuations in the measured values and concluded that they represent cold and warm periods. He numbered the fluctuations by counting backwards from the present at 1. In the period that followed, numerous studies were carried out in this area, and by the early 1970s, numerous additional scientific papers were available that ultimately led to the development of an oxygen isotope stratigraphy of the Quaternary. In the Pleistocene, more than a hundred cycles were distinguished, which correspond to just as many warm-cold periods.
In the mid-1970s, Nicholas Shackleton and James Kennett and Samuel Savin's working group extended the principle to the entire Cenozoic . It was found that the oxygen isotope ratios after the Cretaceous-Paleogene boundary were also subject to significant fluctuations. The rapid changes in isotope ratios observed in the Quaternary are, however, not clearly perceptible, even if individual, well-examined sections show clear indications that such cycles also existed in the Paleogene or in the Neogene .
Marine Oxygen Isotope Stratigraphy of the Quaternary
The current Ice Age is subdivided into 103 isotope stages and numbered backwards from the base of the Quaternary (beginning of the Gelasia ) a little less than 2.6 million years ago. Odd numbers denote the warm periods (interstadials or interglacials), whereas cold periods (glacials) are precisely those. The current warm period corresponds to marine oxygen isotope stage 1 (abbreviated to MIS 1 for the internationally used marine isotope stage 1 ), the "peak" of the last glacial period corresponds to MIS 2. Since further isotope fluctuations could be detected after the first breakdown, additional steps were set up by adding a letter, for example 5e for the Eem warm period .
literature
- James D. Wright: Paleo-oceanography: Cenozoic Climate - Oxygen Isotope Evidence . In: J. Steele, S. Thorpe, K. Turekian (Eds.): Encyclopedia of Ocean Sciences . Academic Press, 2001, doi : 10.1006 / rwos.2001.0252 ( PDF ).
- Lorraine E. Lisiecki, Maureen E. Raymo: A Plio-Pleistocene Stack of 57 Globally Distributed Benthic δ 18 O Records . In: Paleoceanography . tape 20 , 2005 ( PDF file; 1.1 MB ( memento from June 16, 2011 in the Internet Archive )).
Individual evidence
- ^ Wright 2001, p. 7