The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment
We examined the susceptibility of δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios in organic-rich sediments to pre-analysis sample treatment. Each sample was subjected to three different kinds of processing. For comparative purposes, the first measurement serie...
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| Format: | Article |
| Language: | English |
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Pensoft Publishers
2011-08-01
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| Series: | Fossil Record |
| Online Access: | http://www.foss-rec.net/14/141/2011/fr-14-141-2011.pdf |
| _version_ | 1797370325338423296 |
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| author | S. Meisel U. Struck |
| author_facet | S. Meisel U. Struck |
| author_sort | S. Meisel |
| collection | DOAJ |
| description | We examined the susceptibility of δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios in organic-rich sediments to pre-analysis sample treatment. Each sample was subjected to three different kinds of processing. For comparative purposes, the first measurement series (MS-1) was carried out on untreated sediment. In MS-2, the sediment was rinsed with distilled water. In MS-3, analyses were carried out on decalcified and rinsed material, in MS-4 the samples were decalcified without being subsequently washed. The sediment yielded conspicuously different results depending on the type of processing it was subjected to. Rinsing, irrespective of whether acidification was included or not, induced substantial modifications in δ<sup>15</sup>N accompanied by a pronounced loss of NH<sub>4</sub><sup>+</sup> (up to 14 wt% of the initial N-content). Molar C<sub>org</sub>/N ratios, on the other hand, were only affected by a combination of acidification and rinsing. The discrepancies are ascribed to the influence of decomposition-derived ammonium (NH<sub>4</sub><sup>+</sup>). In untreated sediment (MS-1), NH<sub>4</sub><sup>+</sup> seems to produce misleading shifts in both δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios. Presumed mechanisms involved are as follows: Firstly, nitrogen isotopes fractionate during NH<sub>4</sub><sup>+</sup>-volatilisation in the heating oven, where the sediment is put to desiccate. Secondly, NH<sub>4</sub><sup>+</sup>-ions are able to escape that fractionation when adsorbed to negatively-charged SiO<sub>2</sub>-surfaces. The adsorption capacity of SiO<sub>2</sub> increases with increasing pH of the pore water and hence with increasing carbonate content. Our findings raise serious doubts about whether untreated sediment (MS-1) can provide reliable C<sub>org</sub>/N and δ<sup>15</sup>N-records. Pre-analysis acidification plus rinsing (MS-3) seems to eliminate the deceptive influence of NH<sub>4</sub><sup>+</sup>-adsorption and -outgassing.
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doi:<a href="http://dx.doi.org/10.1002/mmng.201100004" target="_blank">10.1002/mmng.201100004</a> |
| first_indexed | 2024-03-08T18:00:49Z |
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| id | doaj.art-f81e9025e5f4445db5b483945d7fafad |
| institution | Directory Open Access Journal |
| issn | 2193-0066 2193-0074 |
| language | English |
| last_indexed | 2024-03-08T18:00:49Z |
| publishDate | 2011-08-01 |
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| spelling | doaj.art-f81e9025e5f4445db5b483945d7fafad2024-01-02T02:22:29ZengPensoft PublishersFossil Record2193-00662193-00742011-08-0114214115210.5194/fr-14-141-2011The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatmentS. Meisel0U. Struck1Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung an der Humboldt-Universität zu Berlin, 10115 Berlin, GermanyMuseum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung an der Humboldt-Universität zu Berlin, 10115 Berlin, GermanyWe examined the susceptibility of δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios in organic-rich sediments to pre-analysis sample treatment. Each sample was subjected to three different kinds of processing. For comparative purposes, the first measurement series (MS-1) was carried out on untreated sediment. In MS-2, the sediment was rinsed with distilled water. In MS-3, analyses were carried out on decalcified and rinsed material, in MS-4 the samples were decalcified without being subsequently washed. The sediment yielded conspicuously different results depending on the type of processing it was subjected to. Rinsing, irrespective of whether acidification was included or not, induced substantial modifications in δ<sup>15</sup>N accompanied by a pronounced loss of NH<sub>4</sub><sup>+</sup> (up to 14 wt% of the initial N-content). Molar C<sub>org</sub>/N ratios, on the other hand, were only affected by a combination of acidification and rinsing. The discrepancies are ascribed to the influence of decomposition-derived ammonium (NH<sub>4</sub><sup>+</sup>). In untreated sediment (MS-1), NH<sub>4</sub><sup>+</sup> seems to produce misleading shifts in both δ<sup>15</sup>N-signals and C<sub>org</sub>/N ratios. Presumed mechanisms involved are as follows: Firstly, nitrogen isotopes fractionate during NH<sub>4</sub><sup>+</sup>-volatilisation in the heating oven, where the sediment is put to desiccate. Secondly, NH<sub>4</sub><sup>+</sup>-ions are able to escape that fractionation when adsorbed to negatively-charged SiO<sub>2</sub>-surfaces. The adsorption capacity of SiO<sub>2</sub> increases with increasing pH of the pore water and hence with increasing carbonate content. Our findings raise serious doubts about whether untreated sediment (MS-1) can provide reliable C<sub>org</sub>/N and δ<sup>15</sup>N-records. Pre-analysis acidification plus rinsing (MS-3) seems to eliminate the deceptive influence of NH<sub>4</sub><sup>+</sup>-adsorption and -outgassing. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201100004" target="_blank">10.1002/mmng.201100004</a>http://www.foss-rec.net/14/141/2011/fr-14-141-2011.pdf |
| spellingShingle | S. Meisel U. Struck The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment Fossil Record |
| title | The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment |
| title_full | The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment |
| title_fullStr | The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment |
| title_full_unstemmed | The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment |
| title_short | The potential distortion of sedimentary δ<sup>15</sup>N and C<sub>org</sub>/N ratios by NH<sub>4</sub><sup>+</sup> and the effects of pre-analysis sample treatment |
| title_sort | potential distortion of sedimentary delta sup 15 sup n and c sub org sub n ratios by nh sub 4 sub sup sup and the effects of pre analysis sample treatment |
| url | http://www.foss-rec.net/14/141/2011/fr-14-141-2011.pdf |
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