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| Titel |
The contribution of tephra constituents during biogenic silica determination: implications for soil and palaeoecological studies |
| VerfasserIn |
W. Clymans, L. Barão, N. Van der Putten, S. Wastegård, G. Gísladóttir, S. Björck, B. Moine, E. Struyf, D. J. Conley |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 12 ; Nr. 12, no. 12 (2015-06-22), S.3789-3804 |
| Datensatznummer |
250117994
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| Publikation (Nr.) |
 copernicus.org/bg-12-3789-2015.pdf |
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| Zusammenfassung |
| Biogenic silica (BSi) is used as a proxy by soil scientists to identify
biological effects on the Si cycle and by palaeoecologists to study
environmental changes. Alkaline extractions are typically used to measure
BSi in both terrestrial and aquatic environments. The dissolution properties
of volcanic glass in tephra deposits and their nanocrystalline weathering
products are hypothesized to overlap those of BSi; however, data to support
this behaviour are lacking. The potential that Si-bearing fractions dissolve
in alkaline media (SiAlk) that do not necessarily correspond to
BSi brings the applicability of BSi as a proxy into question. Here, analysis of 15 samples
reported as tephra-containing allows us to reject the hypothesis that tephra
constituents produce an identical dissolution signal to that of BSi during
alkaline extraction. We found that dissolution of volcanic glass shards is
incomplete during alkaline dissolution. Simultaneous measurement of Al and
Si used here during alkaline dissolution provides an important parameter to
enable us to separate glass shard dissolution from dissolution of BSi and
other Si-bearing fractions. The contribution from volcanic glass shards
(between 0.2 and 4 wt % SiO2), the main constituent of distal tephra,
during alkaline dissolution can be substantial depending on the total
SiAlk. Hence, soils and lake sediments with low BSi concentrations are
highly sensitive to the additional dissolution from tephra constituents and
its weathering products. We advise evaluation of the potential for volcanic
or other non-biogenic contributions for all types of studies using BSi as an
environmental proxy. |
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