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| Titel |
Estimation of the extraterrestrial 3He and 20Ne fluxes on Earth from He and Ne systematics in marine sediments |
| VerfasserIn |
Deborah Chavrit, Manuel Moreira, Frederic Moynier |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132480
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| Publikation (Nr.) |
 EGU/EGU2016-12990.pdf |
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| Zusammenfassung |
| Sediments contain interplanetary dust particles (IDPs) carrying extraterrestrial noble gases,
such as 3He, which have previously been used to estimate the IDP accretion flux over time
and the duration of past environmental events. However, due to its high diffusivity, He can be
lost by diffusion either due to frictional heating during entry in the atmosphere, or once it
has been incorporated in the sediments. Therefore the absolute values of 3He IDP
fluxes cannot be known. Due to its lower diffusivity, Ne is less likely to be lost by
diffusion than He and can potentially provide an absolute IDP flux value. Here, we
studied the Ne and He isotopic composition of 21 sediments of different ages (3 to 38
Myr, 56 Myr and 183 Myr) in order to better constrain the retention of 3He in such
deposits. The samples are carbonates from 2 sites of the Integrated Ocean Drilling
Program (IODP), which previously showed evidence of detectable extraterrestrial
3He, and from the Sancerre core in the Paris basin. The 3He/4He, 20Ne/22Ne and
21Ne/22Ne ratios of decarbonated residues vary respectively from 0.09×10−6 to
76.5×10−6, 9.54±0.08 to 11.30±0.60 and from 0.0295±0.0001 to 0.0344±0.0003.
These isotopic compositions can be explained by a mixing between two terrestrial
components (atmosphere and radiogenic He and nucleogenic Ne present in the
terrigenous fractions) and an extraterrestrial component. The linear relationship
between 20Ne/22Ne and 3He/22Ne ratios shows that the extraterrestrial component has
a unique composition and is similar to the He and Ne composition of implanted
solar wind. This composition is different from the individual stratospheric IDPs for
which the Ne and He isotopic compositions have been measured. We suggest that
this difference is due to a bias in the sampling of the individual IDPs previously
analyzed toward the largest ones that are more likely to lose He during entry in the
atmosphere. Our data further constrains the size of the majority of the IDPs to be less than
10 μm in diameter. In addition, the constant 3He/22Ne ratio of the extraterrestrial
component present in the samples, which is similar to the implanted solar wind
composition, suggests that no diffusive loss of 3He occurred in the atmosphere or on the
seafloor. Thus, neglecting any non-fractionating He and Ne loss by weathering and/or
alteration of the host phases on the seafloor, the extraterrestrial 3He and 20Ne fluxes
between 3 to 38 Myr ago are respectively 0.2±0.1 ×10−12 cm3.cm−2.kyr−1 and
0.2±0.1 ×10−11 cm3.cm−2.kyr−1. During the sharp increases of the late Eocene and
late Miocene, the IDP 3He and 20Ne fluxes reach values up to five times higher. |
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