Zeebe Wolf Gladrow Chapter 3 Book
141
Chapter 3
Stable Isotope Fractionation
In 1913, Sir J.J. Thomson found that the element neon has two different kinds of atoms with atomic weights of 20 and 22, respectively. This was the first experimental proof of a hypothesis by F. Soddy that different atoms might occupy the same place in the Periodic Table. Soddy named these atoms isotopes, which in Greek means equal places (Soddy, 1913). For his experiments, Thomson used a so-called ‘positive ray apparatus’, a predecessor of today’s mass spectrometers (Thomson, 1914). Around 1920, F.W.
Aston greatly improved the apparatus proposed by Thomson and subsequently discovered 212 of the 287 naturally occurring isotopes. In 1931,
Harold C. Urey studied hydrogen by spectroscopic methods and detected a substance that had the same chemical properties as hydrogen but exhibited a larger mass than hydrogen known at this time (Urey et al., 1932). Because the mass was about twice the mass of hydrogen, Urey named it deuterium.
The reason for atoms of the same element having different weights was, however, unclear until the discovery of the neutron by Chadwick in 1932
(Chadwick, 1932).
The discoveries summarized above are milestones at the beginning of a whole branch of science dealing with stable isotopes. Among the different properties of isotopic substances, one is of particular importance for earth sciences: their slightly different physico-chemical behaviors that lead to socalled isotopic fractionation effects. In 1947, Urey published a paper on the thermodynamic properties of isotopic substances (Urey, 1947). This provided the basis for the utilization of stable isotopes in modern disciplines such as stable isotope geochemistry, isotope geology, biogeochemistry, pale-
142
Chapter 3. Stable Isotope Fractionation
oceanography and others. For instance, the analysis of the ratio of stable oxygen isotopes in calcium carbonate, secreted by organisms like belemnites, mollusca, and foraminifera and buried in deep-sea
Chapter 3
Stable Isotope Fractionation
In 1913, Sir J.J. Thomson found that the element neon has two different kinds of atoms with atomic weights of 20 and 22, respectively. This was the first experimental proof of a hypothesis by F. Soddy that different atoms might occupy the same place in the Periodic Table. Soddy named these atoms isotopes, which in Greek means equal places (Soddy, 1913). For his experiments, Thomson used a so-called ‘positive ray apparatus’, a predecessor of today’s mass spectrometers (Thomson, 1914). Around 1920, F.W.
Aston greatly improved the apparatus proposed by Thomson and subsequently discovered 212 of the 287 naturally occurring isotopes. In 1931,
Harold C. Urey studied hydrogen by spectroscopic methods and detected a substance that had the same chemical properties as hydrogen but exhibited a larger mass than hydrogen known at this time (Urey et al., 1932). Because the mass was about twice the mass of hydrogen, Urey named it deuterium.
The reason for atoms of the same element having different weights was, however, unclear until the discovery of the neutron by Chadwick in 1932
(Chadwick, 1932).
The discoveries summarized above are milestones at the beginning of a whole branch of science dealing with stable isotopes. Among the different properties of isotopic substances, one is of particular importance for earth sciences: their slightly different physico-chemical behaviors that lead to socalled isotopic fractionation effects. In 1947, Urey published a paper on the thermodynamic properties of isotopic substances (Urey, 1947). This provided the basis for the utilization of stable isotopes in modern disciplines such as stable isotope geochemistry, isotope geology, biogeochemistry, pale-
142
Chapter 3. Stable Isotope Fractionation
oceanography and others. For instance, the analysis of the ratio of stable oxygen isotopes in calcium carbonate, secreted by organisms like belemnites, mollusca, and foraminifera and buried in deep-sea