EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols
In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox condi...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2012-01-01
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| Series: | Biogeosciences |
| Online Access: | http://www.biogeosciences.net/9/341/2012/bg-9-341-2012.pdf |
| _version_ | 1811283382445801472 |
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| author | N. Glock A. Eisenhauer V. Liebetrau M. Wiedenbeck C. Hensen G. Nehrke |
| author_facet | N. Glock A. Eisenhauer V. Liebetrau M. Wiedenbeck C. Hensen G. Nehrke |
| author_sort | N. Glock |
| collection | DOAJ |
| description | In this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in
tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ)
determined with SIMS. These results are a contribution to a better
understanding of the proxy potential of these elemental ratios for ambient
redox conditions. Foraminiferal tests are often contaminated by diagenetic
coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings.
Thus, it is substantial to assure that the cleaning protocols are efficient
or that spots chosen for microanalyses are free of contaminants. Prior to
the determination of the element/Ca ratios, the distributions of several
elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow
infaunal species <i>Uvigerina peregrina</i> and <i>Bolivina spissa</i> were mapped with an electron microprobe (EMP). To
visualize the effects of cleaning protocols uncleaned and cleaned specimens
were compared. The cleaning protocol included an oxidative cleaning step. An
Fe rich phase was found on the inner test surface of uncleaned <i>U. peregrina</i> specimens.
This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was
found at the inner test surface of <i>B. spissa</i>. Specimens of both species treated with
oxidative cleaning show the absence of this phase. Neither in <i>B. spissa</i> nor in <i>U. peregrina</i> were
any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca
and Fe/Ca ratios of single specimens of <i>B. spissa</i> from different locations have been
determined by secondary ion mass spectrometry (SIMS). Bulk analyses using
solution ICP-MS of several samples were compared to the SIMS data. The
difference between SIMS analyses and ICP-MS bulk analyses from the same
sampling sites was 14.0–134.8 μmol mol<sup>−1</sup> for the Fe/Ca and
1.68(±0.41) μmol mol<sup>−1</sup> for the Mn/Ca ratios. This is in the same order of magnitude
as the variability inside single specimens determined with SIMS at these
sampling sites (1σ<sub>[Mn/Ca]</sub> = 0.35–2.07 μmol mol<sup>−1</sup>; 1σ<sub>[Fe/Ca]</sub> =
93.9–188.4 μmol mol<sup>−1</sup>). The Mn/Ca ratios in the calcite
were generally relatively low (2.21–9.93 μmol mol<sup>−1</sup>) but in the same
magnitude and proportional to the surrounding pore waters (1.37–6.67 μmol mol<sup>−1</sup>).
However, the Fe/Ca ratios in <i>B. spissa</i> show a negative correlation to the
concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca
ratios (87.0–101.0 μmol mol<sup>−1</sup>) were found at 465 m water depth, a
location with a strong sharp Fe peak in the pore water next to the sediment
surface and respectively, high Fe concentrations in the surrounding pore
waters. Previous studies found no living specimens of <i>B. spissa</i> at this location. All
these facts hint that the analysed specimens already were dead before the Fe
flux started and the sampling site just recently turned anoxic due to
fluctuations of the lower boundary of the OMZ near the sampling site (465 m
water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for
redox conditions, if cleaning protocols are carefully applied. The data
presented here may be rated as base for the still pending detailed
calibration. |
| first_indexed | 2024-04-13T02:10:36Z |
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| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-04-13T02:10:36Z |
| publishDate | 2012-01-01 |
| publisher | Copernicus Publications |
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| series | Biogeosciences |
| spelling | doaj.art-97855378fd4042b89f1519171b1807312022-12-22T03:07:19ZengCopernicus PublicationsBiogeosciences1726-41701726-41892012-01-019134135910.5194/bg-9-341-2012EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocolsN. Glock0A. Eisenhauer1V. Liebetrau2M. Wiedenbeck3C. Hensen4G. Nehrke5Sonderforschungsbereich 754, Christian-Albrechts-University Kiel, Climate-Biogeochemistry Interactions in the Tropical Ocean, Kiel, GermanyHelmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR, Wischhofstr. 1–3, 24148 Kiel, GermanyHelmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR, Wischhofstr. 1–3, 24148 Kiel, GermanyHelmholtz-Zentrum Potsdam, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, GermanyHelmholtz-Zentrum für Ozeanforschung Kiel, GEOMAR, Wischhofstr. 1–3, 24148 Kiel, GermanyAlfred Wegener Institut für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, GermanyIn this study we present an initial dataset of Mn/Ca and Fe/Ca ratios in tests of benthic foraminifera from the Peruvian oxygen minimum zone (OMZ) determined with SIMS. These results are a contribution to a better understanding of the proxy potential of these elemental ratios for ambient redox conditions. Foraminiferal tests are often contaminated by diagenetic coatings, like Mn rich carbonate- or Fe and Mn rich (oxyhydr)oxide coatings. Thus, it is substantial to assure that the cleaning protocols are efficient or that spots chosen for microanalyses are free of contaminants. Prior to the determination of the element/Ca ratios, the distributions of several elements (Ca, Mn, Fe, Mg, Ba, Al, Si, P and S) in tests of the shallow infaunal species <i>Uvigerina peregrina</i> and <i>Bolivina spissa</i> were mapped with an electron microprobe (EMP). To visualize the effects of cleaning protocols uncleaned and cleaned specimens were compared. The cleaning protocol included an oxidative cleaning step. An Fe rich phase was found on the inner test surface of uncleaned <i>U. peregrina</i> specimens. This phase was also enriched in Al, Si, P and S. A similar Fe rich phase was found at the inner test surface of <i>B. spissa</i>. Specimens of both species treated with oxidative cleaning show the absence of this phase. Neither in <i>B. spissa</i> nor in <i>U. peregrina</i> were any hints found for diagenetic (oxyhydr)oxide or carbonate coatings. Mn/Ca and Fe/Ca ratios of single specimens of <i>B. spissa</i> from different locations have been determined by secondary ion mass spectrometry (SIMS). Bulk analyses using solution ICP-MS of several samples were compared to the SIMS data. The difference between SIMS analyses and ICP-MS bulk analyses from the same sampling sites was 14.0–134.8 μmol mol<sup>−1</sup> for the Fe/Ca and 1.68(±0.41) μmol mol<sup>−1</sup> for the Mn/Ca ratios. This is in the same order of magnitude as the variability inside single specimens determined with SIMS at these sampling sites (1σ<sub>[Mn/Ca]</sub> = 0.35–2.07 μmol mol<sup>−1</sup>; 1σ<sub>[Fe/Ca]</sub> = 93.9–188.4 μmol mol<sup>−1</sup>). The Mn/Ca ratios in the calcite were generally relatively low (2.21–9.93 μmol mol<sup>−1</sup>) but in the same magnitude and proportional to the surrounding pore waters (1.37–6.67 μmol mol<sup>−1</sup>). However, the Fe/Ca ratios in <i>B. spissa</i> show a negative correlation to the concentrations in the surrounding pore waters. Lowest foraminiferal Fe/Ca ratios (87.0–101.0 μmol mol<sup>−1</sup>) were found at 465 m water depth, a location with a strong sharp Fe peak in the pore water next to the sediment surface and respectively, high Fe concentrations in the surrounding pore waters. Previous studies found no living specimens of <i>B. spissa</i> at this location. All these facts hint that the analysed specimens already were dead before the Fe flux started and the sampling site just recently turned anoxic due to fluctuations of the lower boundary of the OMZ near the sampling site (465 m water depth). Summarized Mn/Ca and Fe/Ca ratios are potential proxies for redox conditions, if cleaning protocols are carefully applied. The data presented here may be rated as base for the still pending detailed calibration.http://www.biogeosciences.net/9/341/2012/bg-9-341-2012.pdf |
| spellingShingle | N. Glock A. Eisenhauer V. Liebetrau M. Wiedenbeck C. Hensen G. Nehrke EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols Biogeosciences |
| title | EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| title_full | EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| title_fullStr | EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| title_full_unstemmed | EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| title_short | EMP and SIMS studies on Mn/Ca and Fe/Ca systematics in benthic foraminifera from the Peruvian OMZ: a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| title_sort | emp and sims studies on mn ca and fe ca systematics in benthic foraminifera from the peruvian omz a contribution to the identification of potential redox proxies and the impact of cleaning protocols |
| url | http://www.biogeosciences.net/9/341/2012/bg-9-341-2012.pdf |
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