Continental degassing of 4He by surficial discharge of deep groundwater

Aggarwal, Pradeep K.; Matsumoto, Takuya; Sturchio, Neil C.; Chang, Hung K.; Gastmans, Didier; Araguas-Araguas, Luis J.; Jiang, Wei; Lu, Zheng-Tian; Mueller, Peter; Yokochi, Reika; Purtschert, Roland; Torgersen, Thomas (2014). Continental degassing of 4He by surficial discharge of deep groundwater. Nature geoscience, 8(1), pp. 35-39. Nature Publishing Group 10.1038/ngeo2302

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Radiogenic He is produced by the decay of uranium and thorium in the Earth’s mantle and crust. From here, it is degassed to the atmosphere and eventually escapes to space. Assuming that all of the 4He produced is degassed, about 70% of the total He degassed from Earth comes from the continental crust. However, the outgoing flux of crustal He has not been directly measured at the Earth’s surface and the migration pathways are poorly understood. Here we present measurements of helium isotopes and the long-lived cosmogenic radio-isotope Kr in the deep, continental-scale Guarani aquifer in Brazil and show that crustal He reaches the atmosphere primarily by the surficial discharge of deep groundwater. We estimate that He in Guarani groundwater discharge accounts for about 20% of the assumed global flux from continental crust, and that other large aquifers may account for about 33%. Old groundwater ages suggest that He in the Guarani aquifer accumulates over half- to one-millionyear timescales. We conclude that He degassing from the continents is regulated by groundwater discharge, rather than episodic tectonic events, and suggest that the assumed steady state between crustal production and degassing of He, and its resulting atmospheric residence time, should be re-examined.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics

UniBE Contributor:

Purtschert, Roland

Subjects:

500 Science > 530 Physics

ISSN:

1752-0894

Publisher:

Nature Publishing Group

Language:

English

Submitter:

Doris Rätz

Date Deposited:

29 Jan 2015 10:27

Last Modified:

10 Sep 2015 10:19

Publisher DOI:

10.1038/ngeo2302

BORIS DOI:

10.7892/boris.62551

URI:

https://boris.unibe.ch/id/eprint/62551

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