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- The isotopic record found in ice cores reveal direct information about the past climate. d18O (delta oxygen-18), 16O and 18O are isotopes of oxygen with slight differences in atomic weight. Depending on the temperature of evaporation and how far the water has had to travel before it fell as snow, the ratio of 18O to
16O will vary. This ratio, known as d18O, can be measured very accurately using a mass spectrometer. Over short time scales the change in temperature from summer to winter produces a very clear oscillation in the 18O/16O ratio. This oscillation is used to determine the age of the core at different depths,
simply by counting the oscillations. Over longer time periods, this ratio indicates the average temperature of the regions between the evaporation site and the coring site. Investigators in Greenland and Antarctica are also analyzing for the ratio of 1H/2H (Hydrogen to deuterium) which will allow even finer detail about source temperature and condensation history to be obtained.
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Abstract from DBPedia | Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) due to different numbers of neutrons in their nuclei. While all isotopes of a given element have almost the same chemical properties, they have different atomic masses and physical properties. The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. It was coined by Scottish doctor and writer Margaret Todd in 1913 in a suggestion to the British chemist Frederick Soddy. The number of protons within the atom's nucleus is called its atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons. The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that every carbon atom has 6 protons so that the neutron numbers of these isotopes are 6, 7, and 8 respectively.同位体(どういたい、英: isotope;アイソトープ)とは、同一原子番号を持つものの中性子数(質量数 A - 原子番号 Z)が異なる核種の関係をいう。この場合、同位元素とも呼ばれる。歴史的な事情により核種の概念そのものとして用いられる場合も多い。 同位体は、放射能を持つ放射性同位体 (radioisotope) とそうではない安定同位体 (stable isotope) の2種類に分類される。 (Source: http://dbpedia.org/resource/Isotope) |