An integrated sulfur isotope model for Namibian shelf sediments

Dale, Andrew W.; Brüchert, Volker; Alperin, Marc J.; Regnier, Pierre

doi:10.1016/j.gca.2008.12.015

Cited by 111 publications

(94 citation statements)

References 85 publications

(138 reference statements)

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“…Total residual OS is typically more 34 S-enriched than its sulfur source, broadly indicating an equilibrium isotope effect in its formation. This relationship holds both in a global compilation of rocks, where pyrite δ 34 S is taken to represent HS s (Bottrell and Raiswell, 2000) and in modern marine sediments (Dale et al, 2009 Based on the above evidence, we propose that OM sulfurization may be associated with equilibrium or kinetic isotope effects under different conditions (Fig. 4).…”

Section: Isotope Effects During Om Sulfurizationmentioning

confidence: 66%

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Raven

Adkins

Werne

et al. 2015

Organic Geochemistry

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Reactions between reduced inorganic sulfur and organic compounds are thought to be important for the preservation of organic matter (OM) in sediments, but the sulfurization process is poorly understood. Sulfur isotopes are potentially useful tracers of sulfurization reactions, which often occur in the presence of a strong porewater isotopic gradient driven by microbial sulfate reduction. Prior studies of bulk sedimentary OM indicate that sulfurized products are 34 Senriched relative to coexisting sulfide, and experiments have produced 34 S-enriched organosulfur compounds. However, analytical limitations have prevented the relationship from being tested at the molecular level in natural environments. Here we apply a new method, coupled gas chromatography -inductively coupled plasma mass spectrometry, to measure the compoundspecific sulfur isotopic compositions of volatile organosulfur compounds over a 6 m core of anoxic Cariaco Basin sediments. In contrast to current conceptual models, nearly all extractable organosulfur compounds were substantially depleted in 34 S relative to coexisting kerogen and 2 porewater sulfide. We hypothesize that this 34 S depletion is due to a normal kinetic isotope effect during the initial formation of a carbon-sulfur bond and that the source of sulfur in this relatively irreversible reaction is most likely the bisulfide anion in sedimentary pore water. The 34 Sdepleted products of irreversible bisulfide addition alone cannot explain the isotopic composition of total extractable or residual OM. Therefore, at least two different sulfurization pathways must operate in the Cariaco Basin, generating isotopically distinct products. Compound-specific sulfur isotope analysis thus provides new insights into the timescales and mechanisms of OM sulfurization.3

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Section: Isotope Effects During Om Sulfurizationmentioning

confidence: 66%

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Raven

Adkins

Werne

et al. 2015

Organic Geochemistry

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“…We also focus on the importance of DNRA to N turnover since previous modeling studies suggest that it may dominate benthic sulfur and nitrogen cycling in suboxic upwelling regions as well as organic-rich costal sediments where sulfide accumulates in the porewater (e.g. Dale et al, 2009;. Furthermore, because of the widespread occurrence of bacterial mats off southern Peru and Chile we expect this process to be significant (e.g.…”

Section: Introductionmentioning

confidence: 99%

Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Bohlen

Dale

Sommer

et al. 2011

Geochimica et Cosmochimica Acta

107

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“…We selected 2 values to estimate the benthic contribution: an average value of + 5.75 ‰ versus VCDT was used as the isotopically light end member representing spatially pooled freeze-dried sediment containing diatoms, benthic meiofauna and sulphur bacteria. An alternative value of -15 ‰ versus VCDT was used as the second end member based on previous measurements at a shelf station at 23°45.5' S, 14°16.0' E in 114 m water depth (Dale et al 2009). We based the use of this value on the fact that sulphur available to grazing gobies is porewater hydrogen sulphide, organic sulphur and elemental sulphur stored in sulphur bacteria, but not mineral sulphides and inorganic sulphate.…”

mentioning

confidence: 99%

“…We based the use of this value on the fact that sulphur available to grazing gobies is porewater hydrogen sulphide, organic sulphur and elemental sulphur stored in sulphur bacteria, but not mineral sulphides and inorganic sulphate. The origin of the sulphides and elemental sulphur is through production by sulphate-reducing bacteria, which fractionate porewater sulphate to derive hydrogen sulphide with a value of -15 ‰ (Dale et al 2009). The fatty acid data were analysed quantitatively (µg mg -1 DW relative to a standard, 23:0) and qualitatively (as percentage of TFA), the latter being useful in situations where samples vary greatly in their TFA content.…”

mentioning

confidence: 99%

Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures

Bank¹,

Utne‐Palm²,

Pittman³

et al. 2011

Mar. Ecol. Prog. Ser.

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The bearded goby Sufflogobius bibarbatus has become a key component of the pelagic food web off Namibia following the crash in pelagic fish populations during the 1970s, and its biomass is increasing despite significant predation pressure and apparent life-history constraints. The integrated feeding of the bearded goby was studied from samples collected during April 2008, using stable isotope ratios (δ 13 C, δ 15 N, δ 34 S) and fatty acids, to resolve conflict amongst previous dietary studies based on gut-content analysis and to understand how diet could influence its success within the region. Isotopes of carbon and nitrogen suggest that the now abundant jellyfish could contribute up to 74% of the diet, and δ 34S signatures indicate that the diatom-and bacteria-rich sulphidic sediments on the central shelf may contribute around 15% to the diet. Fatty acid analyses provided support for sulphur bacterial and jellyfish-feeding amongst gobies, and further suggest that small gobies fed more on zooplankton while large gobies fed more on sedimented diatoms. Both data sets suggest that ontogenetic changes in diet were linked to changes in habitat: pelagic when small, more demersal when large. The study highlights the value of using multiple tracers in trophic studies and indicates that the dietary flexibility of the bearded goby, in conjunction with its behaviour and physiology, likely contributes to its success within the northern Benguela ecosystem.KEY WORDS: Benthic-pelagic coupling · Keystone species · Disturbed ecosystem · Feeding · Aequorea forskalea · Chrysaora fulgida Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 428: [219][220][221][222][223][224][225][226][227][228][229][230][231][232][233] 2011 fish Chrysaora fulgida (Reynaud, 1830) and Aequorea forskalea (Forskål, 1775) (Bakun & Weeks 2006, Lynam et al. 2006. These jellyfish have changed the transfer and flow of energy through the system, with most energy now thought to be channelled from jellyfish directly to the detrital food web (Heymans et al. 2004). The scarcity of sardines has also resulted in an increased sedimentation of primary production (Bakun & Weeks 2006), which contributes to increased regional anoxia (Monteiro et al. 2006).Sufflogobius bibarbatus is an unlikely 'winner' in the changed ecosystem off Namibia, as it is a relatively large, slow-growing gobiid that can attain 140 mm total length (TL) and an age of at least 6 yr (Melo & Le Clus 2005). Reproductive maturity is attained only at 2 to 3 yr of age, and although it is considered to be a serial batch spawner, overall fecundity is not high (Melo & Le Clus 2005). The species is discontinuously distributed between Southern Angola and the Eastern Cape (South Africa), with peaks in abundance mirroring the distribution of the diatomaceous mud belt off central Namibia (Staby & Krakstad 2006). Juvenile gobies generally occur inshore of the 200 m isobath, while larger individuals are more common offshore (O'Toole 1978). Although S. ...

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An integrated sulfur isotope model for Namibian shelf sediments

Cited by 111 publications

References 85 publications

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments

Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Dietary success of a ‘new’ key fish in an overfished ecosystem: evidence from fatty acid and stable isotope signatures

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