In:
Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 103, No. C12 ( 1998-11-15), p. 27931-27946
Abstract:
A new procedure to quantify the components of oceanic helium (“terrigenic” 3 He and 4 He released from the ocean floor and “tritiugenic” 3 He from tritium decay) is described. Terrigenic He and nonatmospheric 3 He (i.e., terrigenic and tritiugenic combined) are obtained in terms of measured concentrations of the He isotopes and also of neon (Ne) (which improves the separation considerably), assuming terrigenic He to vanish in the mixed layer. For the subsequent separation of terrigenic and tritiugenic 3 He, additional information is required and 3 He due to natural tritium represents a complication. The procedure is applied to data from a hydrographic section in the South Atlantic (19°S, 1991) and one in the Eastern Mediterranean (1987). The 1σ data precisions and a systematic error accounting for uncertainties in mixed‐layer He are approximately 0.3%. Sections of the new representations of oceanic He and 3 He and comparisons to the nearest classical quantities (i.e., 3 He, He) are presented. In the South Atlantic the 3 He distribution reflects the hydrographic structure. East of 20°W the average 3 He/ 4 He ratio of terrigenic He below 800 m is 4.5±0.8 times the atmospheric ratio, which implies a substantial contribution of crustal He. In the upper waters, tritiugenic 3 He (0.5 tritium units, ±20%) is separated from terrigenic 3 He. In the Eastern Mediterranean, tritiugenic 3 He is quantified throughout the water column in the presence of substantial levels of terrigenic He; the release rate of terrigenic He from the sea floor is found to be 3.1±1.2 10 10 atoms m −2 s −1 , similar to the rate for continental crust, with a mantle He contribution of 5±1.2% only. Recommendations for future work are to reduce the mentioned systematic error and the uncertainty margins of the He and Ne solubilities and of 3 He due to natural tritium.
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1998
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