Jenk, in Encyclopedia of Quaternary Science (Second Edition), 2013 IntroductionĪnalyses of air bubbles extracted from selected polar ice cores are an accurate and straightforward method of reconstructing the evolution of atmospheric CO 2 concentrations over the past few hundred thousand years. The CO 2 concentration is given in parts per million (ppm), which means parts per million by volume. Most of the CO 2 data, presented in the different figures can be found on the webside of the World Data Center for Paleoclimatology ( ). Analytical methods and possible natural artifacts are discussed in the last two sections. In this article, CO 2 records of different time intervals, starting with the last millennium, are presented and discussed in individual sections.
The discrepancy can, therefore, not be explained by the time resolution of ice-core CO 2 records. However, it was shown that despite the limited time resolution of the Dome C record, it would still detect the reported short-term fluctuations of the stomatal records ( Blunier et al., 2005). Indirect CO 2 measurements from δ 13C in peat and stomatal density and stomatal index measurements on fossil leaves have a better time resolution and suggest century or even decadal variations of atmospheric CO 2 concentration in certain time intervals ( see Quaternary Paleobotony, CO 2 reconstruction from fossil leaves). For the EPICA Dome C ice core it was shown that a deviation of a gas concentration lasting 150 years is still detectable but its amplitude is reduced to about 50% of the original. In ice cores from high accumulation rate sites the time resolution is only a few years, but very long ice-core records are only available from low-accumulation drilling sites, where the time resolution is less precise. The possible time resolution depends on temperature and especially on annual accumulation rates. The mixing of air in the firn and the gradual enclosure process are responsible for the fact that the air in an ice sample does not have a well-defined age, but rather represents a mixture of atmospheric air within a certain age range. The enclosure of bubbles occurs gradually in a depth interval of about 10 m. By comparing CO 2 records from ice cores from different drilling sites with different impurity concentrations and different surface temperatures at drilling sites, it can be estimated that the uncertainty is below about 5 ppm.Ī EPICA: European Project for Ice Coring in Antarctica b DML Dronning Maud Land However, the accuracy of the measurements could be slightly affected by the production or depletion of CO 2 in the air bubbles, as will be discussed in the last section.
The reproducibility, determined by measuring the CO 2 concentration on closely neighboring samples of the same ice core, is between 1.5 and 3 parts per million (ppm) depending on extraction and analytical methods but also on origin and depth of the ice cores. Only ice cores from locations where summer melting can be excluded are suited for such analyses. Stauffer, in Encyclopedia of Quaternary Science, 2007 IntroductionĪnalyses of air bubbles extracted from selected polar ice cores are a very accurate and straight forward method of reconstructing the evolution of atmospheric carbon dioxide (CO 2) concentrations in the past few hundred thousands of years.
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