Terrigenic helium

Marcantonio F., Higgins S., Anderson R. F., Stute M., Schlosser P., and Rasbury E. T. (1998) Terrigenous helium in deep-sea sediments. Geochim. Cosmochim. Acta 62, 1535-1543. 

To separate tritiogenic He from the total He of the water sample (Eqn.3), both " He and neon are used as indicators of atmospheric and terrigenic helium. 

Helium contained in ocean sediments can be interpreted as a mixture of helium from two sources, extraterrestrial and terrigeneous helium (Takayanagi and Ozima 1987 Marcantonio et al. 1995). Contributions from an atmospheric helium component have been shown to be negligible (e g., Farley and Patterson 1995). Assuming that the isotopic compositions of both mixing end-members are known, one can easily calculate the amount of extraterrestrial He, using the following equation ... 

Farley and Patterson 1995). The envelope represents mixing with the two extreme cases of terrigeneous helium signatures analyzed to date sediments derived from old continental crast (e.g., North Atlantic ice-rafted debris with He/ " He = 6xlO , Marcantonio et al. 1998) and sediments from the Amazon River fan ( He/" He = 2xl0 , Marcantonio et al. 1998). 

For the separation of terrigenic helium, neon measurements have to be employed. Two assumptions are (1) that the neon comes only from the atmosphere and also (2) that [Ne/ He]gq = [Ne/ He]air. The terrigenic He component will then become... 

He] is calculated by multiplying the [ Hetenr] calculated from the above equation by the [ He/ He] ratio of the terrigenic helium component, which can be radiogenic helium, mantle helium, or a mixture of both. 

Hem = measured He concentration of the water sample, Hetn = tritiogenic He, eq = He concentration in solubility equilibrium with the atmosphere, Heex = He originating from excess air, and Heter = terrigenic He (crustal and mantle helium). 

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