Crustal He flux

Assuming that the He production in the entire crust is balanced by degassing, an average continental crustal He flux of 2.8x10 ° atoms m s = 3.3x10 ° cm STP cm yr can be derived (O Nions and Oxburgh 1983). This flux may in some cases be useful to estimate the He accumulation rate, but it remains questionable whether the assumption of a uniform flux is justified (e.g., Castro et al. 1998b Ballentine et al. 2002 in this volume Ballentine and Burnard 2002 in this volume). Therefore, He accumulation usually provides only a qualitative timescale. 

In summary, the studies of the Stampriet aquifer highlight all main features of noble gas paleoclimate studies (1) The noble gas temperatures in conjunction with a timescale provide a quantitative record of the glacial/interglacial temperature change, (2) the local long-term relationship between 5 0 and noble gas temperature can be quantified, (3) the excess air record appears to provide additional climatic information related to precipitation, and iv) the accumulation of He provides a qualitative age scale and information on the crustal He flux. 

Based on the observed " He excess and turnover time of the Pacific Ocean Craig et al. (1975) estimated the oceanic " He flux to be 3 lxl0 atoms cm if referred to the area of the entire oceanic crust. This estimate includes both the hydrothermal " He flux emanating from mid-ocean ridges as well as the crustal " He flux by degassing of fhe oceanic crust. The oceanic " He flux is small compared to the total " He flux of ca. 1.3x10 afoms cm s (normalized fo fhe entire earth surface). 

In the case of subducting area, however, Van Soest, Hilton, and Kreulen (1998) called attention to the importance of the arc crust carbon in the C/He flux the crustal... 

TorgersenT. and Clarke W. B. (1985) Helium accumulation in groundwater I. An evaluation of sources and the continental flux of crustal He in the Great Artesian Basin, Australia. Geochim. Cosmochim. Acta 49, 1211-1218. 

Province Total Heat flux mW Crustal Heat Flux mW m " He flux cm STP m Heat flux from " He mW m Heat balance... 

He/ °Ar ratio close to that of the crustal production. The required " "Ar flux was estimated to be comparable to that produced by the whole crust. However, they noted that this flux is decoupled from the " He flux and has to be discontinuous in time and space. The difference between He and Ar was attributed to several factors including heterogeneous distribution of U, Th and K, differential release of noble gas isotopes from... 

The analytical model was calibrated with an external flux to the bottom of the aquifer of 3.6 X 10 cm STP cm H is important to note that this flux represents only part of the local integrated crustal production as a consequence of downstream He dilution in the deeper aquifer. Thus, this flux is smaller than the average crustal flux calculated for the GAB by Torgersen and Clarke (1985) (3.62 X 10 cm STP yr ) or that calculated for the Paris Basin by... 

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