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FIGURE 3.13 Thermohaline circulation, commonly referred to as the ocean “conveyor belt,” is made up of ocean currents that transport heat from the tropics to the polar regions. AMS of the radioactive isotope argon-39 will be used to explore this conveyor belt and its impact on climate. SOURCE: National Oceanic and Atmospheric Administration.

is comparable to the amount transported by the atmosphere. Therefore, it is very important to understand this system. With a half-life of 269 years, argon-39 is particularly well suited to study questions related to ocean circulation. However, its extremely low concentration (argon-39/Ar = 8.1 × 10−16), coupled to its long half-life, makes it impossible to measure the argon-39 decay in any sample of reasonable size.4

AMS using the ATLAS heavy ion accelerator at Argonne National Laboratory has been successful in separating argon-39 from its ubiquitous potassium-39 iso-baric background, the latter being 6-7 orders of magnitude more intense. Measurement of isotopic ratios as small as argon-39/Ar = 4 × 10−17 have been achieved. This program is now poised to measure argon-39 concentrations in ocean water samples in order to explore the oceanic “conveyor belt.”

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4 Portions of this paragraph have been adapted from M. Gaelens, M. Loiselet, G. Ryckewaert, et al., 2004, Oceans circulation and electron cyclotron resonance sources: Measurement of the AR-39 isotopic ratio in seawater, Review of Scientific Instruments 75: 1916.



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