Si/C decoupling in the world ocean: is the Southern Ocean different?

Ragueneau, Olivier; Dittert, Nicolas; Pondaven, Philippe; Tréguer, Paul; Corrin, Lydie

doi:10.1016/s0967-0645(02)00075-9

Cited by 71 publications

(85 citation statements)

References 116 publications

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“…The annual integrated Si:C production ratio, derived from Leblanc et al (2003), was estimated to be 0.03 ( Si/ C=0.14 mol Si/4.5 mol C m −2 y −1 ), which is similar to values found in the Equatorial Pacific (review in Ragueneau et al, 2000). Average annual Si:C export ratios increased to 0.09 at 56 m and 0.14 at 142 m and were comparable to those observed in other open ocean oligotrophic sites such as BATS and PAP (Ragueneau et al, 2002).…”

Section: Si/c Decouplingsupporting

confidence: 81%

Efficiency of the silicate pump at a coastal oligotrophic site in the Mediterranean Sea

et al. 2005

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Abstract.A one-year survey of the sedimenting particulate material was conducted at the SOFi site located on the edge of the continental slope in the Gulf of Lions (Northwestern Mediterranean) between September 1999 and December 2000. The main focus of this paper was to establish an annual budget of biogenic silica export, to describe the seasonnal pattern of Si fluxes in relation to the organic and mineral C fluxes and to quantify the Si/C decoupling processes during sedimentation. The pattern of the downward flux of BSi was partly typical with increased daily sedimentation rates during spring followed by smaller peaks during summer. However, an unusual sedimentation event was recorded in the bottom trap in February before the spring thermal stratification occurred, and represented 37% of the annual BSi mass flux. The total annual BSi flux at the SOFi site was estimated from the bottom trap and amounted to 86.8 mmol Si m −2 y −1 , while the organic carbon flux amounted to 154.9 mmol C m −2 y −1 . The overall efficiency of C export to depth compared to surface primary production budgets was low (3%) and similar to values found for oligotrophic regions of the Eastern Mediterranean. On the other hand, we documented a very high efficiency of the Si export at the SOFi site, with 62% of the Si produced in the surface layer exported to the bottom trap. The excellent correlation between BSi and particulate organic C (POC) in the bottom trap further indicates that the bulk of the organic matter is transferred to depth in association with diatoms. However, the main fraction of the C produced by phytoplankton is lost in the water column through oxidation or metabolisation, while biogenic silica is more efficiently transferred to depth. This strong Si/C decoupling with depth is likely to be the cause of the spring Correspondence to: K. Leblanc (leblanc@com.univ-mrs.fr) depletion of silicic acid over the entire water column which was observed by mid-April in a companion study (Leblanc et al., 2003) and may cause a severe Si limitation of the diatom spring bloom in this oligotrophic region of the Gulf of Lions.

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Section: Si/c Decouplingsupporting

confidence: 81%

Efficiency of the silicate pump at a coastal oligotrophic site in the Mediterranean Sea

et al. 2005

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“…The molar Si to POC ratios (Si/C) of standing stocks mirrored the changes in bSiO 2 concentrations rather than reflecting overall patterns in the POC standing stocks (Figure 5F). Outside the mesocosms, Si/C ratios were around 0.015, which is similar to the lowest ratios reported for North Atlantic Waters (Ragueneau et al, 2002). The +Si mesocosms had Si/C ratios of 0.04-0.10, similar to global ocean average (0.04-0.25, Ragueneau et al, 2002).…”

Section: Standing Stocks and Phytoplankton Compositionsupporting

confidence: 67%

Copepods Boost the Production but Reduce the Carbon Export Efficiency by Diatoms

et al. 2018

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The fraction of net primary production that is exported from the euphotic zone as sinking particulate organic carbon (POC) varies notably through time and from region to region. Phytoplankton containing biominerals, such as silicified diatoms have long been associated with high export fluxes. However, recent reviews point out that the magnitude of export is not controlled by diatoms alone, but determined by the whole plankton community structure. The combined effect of phytoplankton community composition and zooplankton abundance on export flux dynamics, were explored using a set of 12 large outdoor mesocosms. All mesocosms received a daily addition of minor amounts of nitrate and phosphate, while only 6 mesocosms received silicic acid (dSi). This resulted in a dominance of diatoms and dinoflagellate in the +Si mesocosms and a dominance of dinoflagellate in the −Si mesocosms. Simultaneously, half of the mesocosms had decreased mesozooplankton populations whereas the other half were supplemented with additional zooplankton. In all mesocosms, POC fluxes were positively correlated to Si/C ratios measured in the surface community and additions of dSi globally increased the export fluxes in all treatments highlighting the role of diatoms in C export. The presence of additional copepods resulted in higher standing stocks of POC, most probably through trophic cascades. However it only resulted in higher export fluxes for the −Si mesocosms. In the +Si with copepod addition (+Si +Cops) export was dominated by large diatoms with higher Si/C ratios in sinking material than in standing stocks. During non-bloom situations, the grazing activity of copepods decrease the export efficiency in diatom dominated systems by changing the structure of the phytoplankton community and/or preventing their aggregation. However, in flagellate-dominated system, the copepods increased phytoplankton growth, aggregation and fecal pellet production, with overall higher net export not always visible in term of export efficiency.

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“…A number of possible explanations for the observed correlations were evaluated as follows: There is obviously no close coupling of BSi and OM in the particle flux to the seafloor and within the sediment which could explain the correlation of Si:O 2 fluxes. Although both BSi and OM are major components of diatoms that are found in certain ratios in the living organisms (Ragueneau et al, 2000, the biogeochemical cycles of silicon and carbon decouple both vertically and horizontally in the water column (Rivkin et al, 1996;Gallinari et al, 2002;Ragueneau et al, 2002). Considering the multitude of water depths, and the different regions investigated, related concentrations in the particle rain reaching the seafloor are highly unlikely.…”

Section: Discussionmentioning

confidence: 99%

“…The good correlation of the kinetic rate constants k andk indicates that the kinetics of BSi dissolution is related to the kinetics of OM degradation, rather than to an intrinsic property of the solid BSi phase, as the latter would require a close coupling of BSi and OM in the particle downflux, which is not the case. Further investigations that integrate studies on how BSi and OM are associated within particles (Schrader, 1971;Tande and Slagstad, 1985;Ragueneau et al, 2002), the structure of diatom skeletons (Hecky et al, 1973;Wetherbee et al, 2000;Volcani, 2002), and models on the use and spreading of hydrolytic enzymes by bacteria (Vetter et al, 1998;Rothman and Forney, 2007) are necessary to elucidate the conditions under which bacteria may mediate BSi dissolution, and the low impact of sediment opal contents on its dissolution rate.…”

Section: Kinetics and Reactive Surface Areamentioning

confidence: 99%

Microbial mediation of benthic biogenic silica dissolution

Holstein

Hensen

2009

Geo-Mar Lett

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Pore water profiles from 24 stations in the South Atlantic (located in the Guinea, Angola, Cape, Guyana, and Argentine basins) show good correlations of oxygen and silicon, suggesting microbially mediated dissolution of biogenic silica. We used simple analytical transport and reaction models to show the tight coupling of the reconstructed process kinetics of aerobic respiration and silicon regeneration. A generic transport and reaction model successfully reproduced the majority of Si pore water profiles from aerobic respiration rates, confirming that the dissolution of biogenic silica (BSi) occurs proportionally to O 2 consumption. Possibly limited to well-oxygenated sediments poor in BSi, benthic Si fluxes can be inferred from O 2 uptake with satisfactory accuracy. Compared to aerobic respiration kinetics, the solubility of BSi emerged as a less influential parameter for silicon regeneration. Understanding the role of bacteria for silicon regeneration requires further investigations, some of which are outlined. The proposed aerobic respiration control of benthic silicon cycling is suitable for benthic-pelagic models. The empirical relation of BSi dissolution to aerobic respiration can be used for regionalization assessments and estimates of the silicon budget to increase the understanding of global primary and export production patterns.

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Si/C decoupling in the world ocean: is the Southern Ocean different?

Cited by 71 publications

References 116 publications

Efficiency of the silicate pump at a coastal oligotrophic site in the Mediterranean Sea

Efficiency of the silicate pump at a coastal oligotrophic site in the Mediterranean Sea

Copepods Boost the Production but Reduce the Carbon Export Efficiency by Diatoms

Microbial mediation of benthic biogenic silica dissolution

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