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Marine isotopic stage
From Wikipedia, the free encyclopedia
Marine isotopic stages (MIS) are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting temperature curves derived from data from deep sea core samples.
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Each stage is a period of higher or lower temperature on a graph of mean temperature (y-axis) versus millions, hundreds of thousands or thousands of years (x-axis). The cycles were found to correspond to terrestrial evidence of glacials and interglacials. A graph of the entire series of stages then revealed hitherto unknown and unsuspected advances and retreats of ice and also filled in the details of the stadials and interstadials. More recent core samples of today's glacial ice substantiated the cycles through studies of ancient pollen deposition. Currently a number of methods are making additional detail possible.
Each stage represents a glacial, interglacial, stadial or interstadial. Interglacials are odd-numbered; glacials are even numbered, one for each stage, starting from the present and working backward in time. For example, the Holocene is MIS1, or O-stage 1, or just stage 1. The previous interglacial is MIS5, or O-stage 5, or just stage 5.
Exceptionally, MIS2-4 refer to the last glacial, because when initially interpreted MIS3 looked like an interglacial.
Stadials and interstadials are identified by a letter following the corresponding glacial or interglacial: 5a, 5b, etc. The dates of the stages were obtained by calibrating the graph on known dates by other methods.
MIS 11 of approximately 400ka is the most similar to MIS 1. A difference that has puzzled scientists is that CO2 levels remained steady or rose during MIS1 (before the industrial era), when by analogy to past interglacials, they should have been steadily decreasing over the last 5000 years. This is the basis of the Early anthropocene hypothesis.
Matching the stages to named periods proceeds as new dates are discovered and new regions are explored geologically. The process is challenging, however, since the marine isotopic record appears more complete and detailed than any terrestrial equivalents. The MIS data for the last 2.5 million years show "about fifty climate cycles...so far not even half these cycles have been identified on land..."[1] A current timeline of glaciation for the Plio-Pleistocene represents a version of this ongoing endeavor.
- ^ Koster, Eduard A., ed. The Physical Geography of Western Europe. Oxford, Oxford University Press, 2005; p. 41.