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| Titel |
Reconstruction of the biogeochemistry and ecology of photoautotrophs based on the nitrogen and carbon isotopic compositions of vanadyl porphyrins from Miocene siliceous sediments |
| VerfasserIn |
Y. Kashiyama, N. O. Ogawa, M. Shiro, R. Tada, H. Kitazato, N. Ohkouchi |
| 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 ; 5, no. 3 ; Nr. 5, no. 3 (2008-05-15), S.797-816 |
| Datensatznummer |
250002523
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| Publikation (Nr.) |
 copernicus.org/bg-5-797-2008.pdf |
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| Zusammenfassung |
| We determined both the nitrogen and carbon isotopic compositions of various
vanadyl alkylporphyrins isolated from siliceous marine sediments of the
Onnagawa Formation (middle Miocene, northeastern Japan) to investigate the
biogeochemistry and ecology of photoautotrophs living in the paleo-ocean.
The distinctive isotopic signals support the interpretations of previous
works that the origin of 17-nor-deoxophylloerythroetioporphyrin (DPEP) is
chlorophylls-c1-3, whereas 8-nor-DPEP may have originated from
chlorophylls-a2 or b2 or bacteriochlorophyll-a. Although DPEP and
cycloheptanoDPEP are presumably derived from common precursory pigments,
their isotopic compositions differed in the present study, suggesting that
the latter represents a specific population within the photoautotrophic
community. The average δ15N value for the entire
photoautotrophic community is estimated to be –2 to +1‰ from the δ15N values of DPEP (–6.9 to –3.6‰; n=7), considering that the
empirical isotopic relationships that the tetrapyrrole nuclei of
chloropigments are depleted in 15N by ~4.8‰ and enriched in
13C by ~1.8‰ relative to the whole cells. This
finding suggests that nitrogen utilized in the primary production was
supplied mainly through N2-fixation by diazotrophic cyanobacteria.
Based on the δ13C values of DPEP (–17.9 to –15.6‰; n=7), we
estimated isotopic fractionation associated with photosynthetic carbon
fixation to be 8–14‰. This range suggests the importance of β-carboxylation and/or active transport of the carbon substrate, indicating
in turn the substantial contribution of diazotrophic cyanobacteria to
primary production. Based on the δ15N values of 17-nor-DPEP
(–7.4 to –2.4‰ n=7), the δ15N range of chlorophylls-c-producing algae was estimated to be –3 to +3‰. This relative depletion in
sup>15N suggests that these algae mainly utilized nitrogen regenerated from
diazotrophic cyanobacteria. Given that diatoms are likely to have
constituted the chlorophylls-c-producing algae within the
biogenic-silica-rich Onnagawa Formation, cyanobacteria-hosting diatoms may
have been important contributors to primary production. |
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