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Thomson, J; Crudeli, D; De Lange, Gj; Slomp, Cp; Erba, E; Corselli, C; Calvert, Se. |
High relative concentrations of the lower photic zone nannofossil Florisphaera profunda have been reported in all recent eastern Mediterranean sapropels. In the most recent sapropel (S1), high bulk sediment Sr/Ca ratios occur along with high F. profunda contents toward the base of the unit, exemplified here in four cores from 1.5-3.5 km water depth. Co-occurring biogenic carbonates contain insufficient Sr to account for these high Sr concentrations, and X-ray diffraction and selective leaching show that the high Sr/Ca ratios are due to aragonite, the CaCO3 polymorph that is rarely preserved in deep marine sediments, with similar to1 wt % Sr. The possible sources of this aragonite include ( 1) precipitation with surface ocean production, ( 2) detrital input... |
Tipo: Text |
Palavras-chave: Sapropel; Aragonite; Strontium. |
Ano: 2004 |
URL: https://archimer.ifremer.fr/doc/00229/33975/32412.pdf |
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Galbraith, Ed; Kienast, M; Pedersen, Tf; Calvert, Se. |
An analysis of sedimentary nitrogen isotope records compiled from widely distributed marine environments emphasizes the global synchrony of denitrification changes and provides evidence for a strong temporal coupling of these variations to changes in nitrogen fixation as previously inferred. We explain the global coherence of these records by a simple physical control on the flux of dissolved oxygen to suboxic zones and the coupling to fixation via the supply of phosphorus to diazotrophs in suitable environments. According to our hypothesis, lower glacial-stage sea surface temperature increased oxygen solubility, while stronger winds in high-latitude regions enhanced the rate of thermocline ventilation. The resultant colder, rapidly flushed thermocline... |
Tipo: Text |
Palavras-chave: Isotopes; Fixation; Denitrification. |
Ano: 2004 |
URL: https://archimer.ifremer.fr/doc/00229/34026/32421.pdf |
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Kienast, M; Higginson, Mj; Mollenhauer, G; Eglinton, Ti; Chen, Mt; Calvert, Se. |
The bulk sedimentary nitrogen isotopic composition of two cores from nearby sites on the northern slope of the South China Sea ( Site 17940 and Ocean Drilling Program (ODP) Site 1144) differs by up to > 2 parts per thousand during the last glacial period. Given their close proximity, both core sites are located in the same biogeographic zone and nutrient regime, and it is thus unlikely that this offset is due to a true gradient in surface ocean conditions. In an attempt to resolve this offset, we have investigated the possible effects of two sedimentological parameters that can affect bulk sedimentary delta(15)N, namely, the variable contribution of inorganic N to bulk N in the sediment and the grain-size dependence of bulk delta(15)N. We find that... |
Tipo: Text |
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Ano: 2005 |
URL: https://archimer.ifremer.fr/doc/00230/34076/32639.pdf |
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