Chlorine-36 and the initial value problem

Stanley N. Davis, DeWayne Cecil, Marek G Zreda, Pankaj Sharma

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

Chlorine-36 is a radionuclide with a half-life of 3.01 × 105a. Most 36Cl in the hydrosphere originates from cosmic radiation interacting with atmospheric gases. Large amounts were also produced by testing thermonuclear devices during 1952-58. Because the monovalent anion, chloride, is the most common form of chlorine found in the hydrosphere and because it is extremely mobile in aqueous systems, analyses of both total Cl- as well as 36Cl have been important in numerous hydrologic studies. In almost all applications of 36Cl, a knowledge of the initial, or pre-anthropogenic, levels of 36CL is useful, as well as essential in some cases. Standard approaches to the determination of initial values have been to: (a) calculate the theoretical cosmogenic production and fallout, which varies according to latitude; (b) measure 36CL in present-day precipitation and assume that anthropogenic components can be neglected; (c) assume that shallow ground-water retains a record of the initial concentration; (d) extract 36CL from vertical depth profiles in desert soils; (e) recover 36CL from cores of glacial ice; and (f) calculate subsurface production of 36CL for water that has been isolated from the atmosphere for more than one million years. The initial value from soil profiles and ice cores is taken as the value that occurs directly below the depth of the easily defined bomb peak. All six methods have serious weaknesses. Complicating factors include 36CL concentrations not related to cosmogenic sources, changes in cosmogenic production with time, mixed sources of chloride in groundwater, melting and refrrezing of waterin glaciers, and seasonal groungwater recharge that does not contain average year-long concentrations of 36Cl.

Original languageEnglish (US)
Pages (from-to)104-114
Number of pages11
JournalHydrogeology Journal
Volume6
Issue number1
StatePublished - 1998

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chlorine isotope
hydrosphere
chloride
desert soil
groundwater
atmospheric gas
fallout
ice core
half life
soil profile
radionuclide
anion
chlorine
recharge
glacier
melting
ice
atmosphere
water
method

ASJC Scopus subject areas

  • Earth and Planetary Sciences (miscellaneous)
  • Water Science and Technology

Cite this

Davis, S. N., Cecil, D., Zreda, M. G., & Sharma, P. (1998). Chlorine-36 and the initial value problem. Hydrogeology Journal, 6(1), 104-114.

Chlorine-36 and the initial value problem. / Davis, Stanley N.; Cecil, DeWayne; Zreda, Marek G; Sharma, Pankaj.

In: Hydrogeology Journal, Vol. 6, No. 1, 1998, p. 104-114.

Research output: Contribution to journalArticle

Davis, SN, Cecil, D, Zreda, MG & Sharma, P 1998, 'Chlorine-36 and the initial value problem', Hydrogeology Journal, vol. 6, no. 1, pp. 104-114.
Davis SN, Cecil D, Zreda MG, Sharma P. Chlorine-36 and the initial value problem. Hydrogeology Journal. 1998;6(1):104-114.
Davis, Stanley N. ; Cecil, DeWayne ; Zreda, Marek G ; Sharma, Pankaj. / Chlorine-36 and the initial value problem. In: Hydrogeology Journal. 1998 ; Vol. 6, No. 1. pp. 104-114.
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