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| Titel |
Nitrogen isotopes in bulk marine sediment: linking seafloor observations with subseafloor records |
| VerfasserIn |
J.-E. Tesdal, E. D. Galbraith, M. Kienast |
| 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 ; 10, no. 1 ; Nr. 10, no. 1 (2013-01-09), S.101-118 |
| Datensatznummer |
250017461
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| Publikation (Nr.) |
 copernicus.org/bg-10-101-2013.pdf |
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| Zusammenfassung |
| The stable isotopes of nitrogen offer a unique perspective on changes in the
nitrogen cycle, past and present. However, the presence of multiple forms of
nitrogen in marine sediments can complicate the interpretation of bulk nitrogen
isotope measurements. Although the large-scale global patterns of seafloor δ15N
have been shown to match process-based expectations, small-scale heterogeneity on
the seafloor, or alterations of isotopic signals during translation into the
subseafloor record, could obscure the primary signals. Here, a public database of nitrogen isotope
measurements is described, including both seafloor and subseafloor sediment samples
ranging in age from modern to the Pliocene, and used to assess these uncertainties.
In general, good agreement is observed between neighbouring seafloor sites within
a 100 km radius, with 85% showing differences of < 1‰. There is
also a good correlation between the δ15N of the shallowest (< 5 ka)
subseafloor sediments and neighbouring seafloor sites within
a 100 km radius (R2 = 0.83), which suggests a reliable translation of
sediments into the buried sediment record. Meanwhile, gradual
δ15N decreases over multiple glacial–interglacial cycles appear to
reflect post-depositional alteration in records from the deep sea (below 2000 m).
We suggest a simple conceptual model to explain these 100-kyr-timescale changes
in well-oxygenated, slowly accumulating sediments, which calls on differential
loss rates for pools of organic N with different δ15N. We conclude
that bulk sedimentary nitrogen isotope records are reliable monitors of past
changes in the marine nitrogen cycle at most locations, and could be further
improved with a better understanding of systematic post-depositional alteration.
Furthermore, geochemical or environmental criteria should be developed in order to effectively identify problematic locations
and to account for confounding influences where possible. |
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