Ocean Circulation/Mixing Studies with Decay-Series Isotopes.

Ku, Teh-Lung and Luo, Shangde (2008) Ocean Circulation/Mixing Studies with Decay-Series Isotopes. In: U-Th series nuclides in aquatic systems. , ed. by Krishnaswami, S. and Cochran, J. Kirk. Radioactivity in the environment, 13 . Elsevier, Amsterdam, pp. 307-344. DOI 10.1016/S1569-4860(07)00009-5.

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Abstract

This chapter summarizes the efforts to use naturally occurring U- and Th-decay series nuclides as tracers of ocean circulation/mixing in open-ocean and coastal environments. The decay-series isotopes that have been exploited for ocean mixing studies are the four radium isotopes (226Ra, 228Ra, 224Ra, and 223Ra), 222Rn, and 227Ac. In addition, particle-reactive radionuclides (230Th, 231Pa, and 210Pb) have been used to constrain basin-wide water residence or ventilation times. Isotopes of radium, 222Rn, and 227Ac have been used to trace mixing and circulation in the ocean because of their relatively high solubility in seawater and suitable half-lives. 226Ra has a suitable radioactive mean-life, ∼2,300y, for large-scale oceanic mixing studies. The small-scale temporal and spatial variability generally associated with coastal mixing processes accentuates the integrating power of the 228Ra tracer. Along with the three other radium isotopes of the “radium quartet,” 228Ra is steadily input to coastal waters by desorption and diffusion from shelf, estuarine, and/or marsh sediments and through submarine groundwater discharge. Water close to the shore thus has a continual supply of these Ra isotopes despite their short decay lives. Produced in seawater by the decay of 226Ra, 222Rn in the ocean has activities equal to those of 226Ra except in regions of the air–sea and sediment–sea interfaces. Exceptionally high apparent vertical mixing has been observed in deep-ocean passages, where the interplay between strong bottom water flows, manganese nodule occurrence, and high standing crop of excess 222Rn is much in evidence. Several studies have explored the use of 227Ac for tracing basin-wide circulation and mixing on decadal time-scales. The potential of 227Ac as a tracer appears to lie chiefly in assessing diapycnal mixing in the deep sea.

Document Type: Book chapter
Additional Information: Das Buch ist in der GEOMAR-Bibliothek vorhanden.
Keywords: Ocean circulation, Decay-series isotopes
Publisher: Elsevier
Projects: Enrichment
Date Deposited: 05 Oct 2016 08:04
Last Modified: 05 Oct 2016 08:04
URI: https://oceanrep.geomar.de/id/eprint/34109

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