Seasonal evolution of net and regenerated silica production around a natural Fe-fertilized area in the Southern Ocean estimated with Si isotopic approaches

Closset, Ivia; Lasbleiz, M.; Leblanc, Karine; Quéguiner, Bernard; Cavagna, A.-J.; Elskens, Marc; Navez, Jacques; Cardinal, Damien

doi:10.5194/bg-11-5827-2014

Cited by 47 publications

(60 citation statements)

References 69 publications

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“…Significant nitrification can also explain why silicic acid is depleted (with high biogenic silica production : dissolution ratio) but not nitrate (Mosseri et al, 2008;Closset et al, 2014). Si : NO 3 assimilation ratios were close to 1 (Mosseri et al, 2008;Closset et al, 2014), in accordance with what is expected for nonlimiting iron conditions (Takeda, 1998;Hutchins and Bruland, 1998).…”

Section: A J Cavagna Et Al: N Cycling In the Vicinity Of Kerguelensupporting

confidence: 75%

“…South of the polar front, mixed layer macronutrient levels were high and their distributions were relatively uniform between stations Closset et al, 2014), with an average nitrate concentration of ∼ 25 µmol L −1 (Fig. 2a).…”

Section: Resultsmentioning

confidence: 99%

“…Indeed, the maximum difference in temperature was less than 2 • C and according to the growth-temperature relationship described in Eppley (1972) such a small range of temperature cannot explain the large change in growth rate. Throughout the study period the uniformly high macronutrient concentrations Closset et al, 2014;Fig. 2) remained at levels preventing any Si, P, or N limitation of phytoplankton growth (e.g. Sarthou et al, 2005, and reference therein).…”

Section: High Primary Production In Naturally Iron-fertilized Bloomsmentioning

confidence: 99%

“…Given the low underestimation, uncorrected ammonium uptake rates will be presented and discussed. Moreover, we opted for long incubation times in order to enhance sensitivity for detection of nitrification and to enable the comparison with Si uptake and dissolution experiments carried out over similar 24 h periods (Closset et al, 2014).…”

Section: A J Cavagna Et Al: N Cycling In the Vicinity Of Kerguelenmentioning

confidence: 99%

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Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

et al. 2015

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Abstract. Although the Southern Ocean is considered a high-nutrient, low-chlorophyll (HNLC) area, massive and recurrent blooms are observed over and downstream of the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N uptake (NO − 3 and NH + 4 ), and nitrification rates were measured at eight stations in austral spring 2011 (October-November) during the KEOPS 2 cruise in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production, with mixed layer integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m −2 d −1 and up to 0.31 d −1 respectively) compared to the HNLC reference site (12 mmol C m −2 d −1 and 0.06 d −1 respectively). Primary production was mainly sustained by nitrate uptake, with f ratios (corresponding to NO − 3 -uptake / (NO − 3 -uptake + NH + 4 -uptake)) lying at the upper end of the observations for the Southern Ocean (up to 0.9). We report high rates of nitrification (up to ∼ 3 µmol N L −1 d −1 , with ∼ 90 % of them < 1 µmol N L −1 d −1 ) typically occurring below the euphotic zone, as classically observed in the global ocean. The specificity of the studied area is that at most of the stations, the euphotic layer was shallower than the mixed layer, implying that nitrifiers can efficiently compete with phytoplankton for the ammonium produced by remineralization at low-light intensities. Nitrate produced by nitrification in the mixed layer below the euphotic zone is easily supplied to the euphotic zone waters above, and nitrification sustained 70 ± 30 % of the nitrate uptake in the productive area above the Kerguelen Plateau. This complicates estimations of new production as potentially exportable production. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.

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Section: A J Cavagna Et Al: N Cycling In the Vicinity Of Kerguelensupporting

confidence: 75%

Section: Resultsmentioning

confidence: 99%

Section: High Primary Production In Naturally Iron-fertilized Bloomsmentioning

confidence: 99%

Section: A J Cavagna Et Al: N Cycling In the Vicinity Of Kerguelenmentioning

confidence: 99%

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Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

et al. 2015

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“…Indeed, surface waters had 10 % less nitrate than winter water (26 µM at 5 m vs. 29 µM at 200 m), and the isotopic enrichment of this surface nitrate confirmed a suggestion of uptake (see Dehairs et al, 2014). Also, reported relatively low Si : C and Si : N ratios for surface ocean suspended matter), pointing to the development of a diatom assemblage just prior to the sampling, consistent with the high dissolution rates of biogenic silica (BSi) that Closset et al (2014) reported for R-2 surface waters. It is therefore likely that the mesopelagic Ba xs content at R-2 indeed reflects remineralization of organic material that was fuelled by an important past early spring production and export event.…”

Section: Depth-weighted Average Ba Xs Content Of Mesopelagic Waterssupporting

confidence: 65%

Early spring mesopelagic carbon remineralization and transfer efficiency in the naturally iron-fertilized Kerguelen area

et al. 2015

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Abstract. We report on the zonal variability of mesopelagic particulate organic carbon remineralization and deep carbon transfer potential during the Kerguelen Ocean and Plateau compared Study 2 expedition (KEOPS 2; OctoberNovember 2011) in an area of the polar front supporting recurrent massive blooms from natural Fe fertilization. Mesopelagic carbon remineralization (MR) was assessed using the excess, non-lithogenic particulate barium (Ba xs ) inventories in mesopelagic waters and compared with bacterial production (BP), surface primary production (PP) and export production (EP). Results for this early season study are compared with the results obtained during a previous study (2005; KEOPS 1) for the same area at a later stage of the phytoplankton bloom. Our results reveal the patchiness of the seasonal advancement and of the establishment of remineralization processes between the plateau (A3) and polar front sites during KEOPS 2. For the Kerguelen plateau (A3 site) we observe a similar functioning of the mesopelagic ecosystem during both seasons (spring and summer), with low and rather stable remineralization fluxes in the mesopelagic column (150-400 m). The shallow water column (∼ 500 m), the lateral advection, the zooplankton grazing pressure and the pulsed nature of the particulate organic carbon (POC) transfer at A3 seem to drive the extent of MR processes on the plateau. For deeper stations (> 2000 m) located on the margin, inside a polar front meander, as well as in the vicinity of the polar front, east of Kerguelen, remineralization in the upper 400 m in general represents a larger part of surface carbon export. However, when considering the upper 800 m, in some cases, the entire flux of exported carbon is remineralized. In the polar front meander, where successive stations form a time series, two successive events of particle transfer were evidenced by remineralization rates: a first mesopelagic and deep transfer from a past bloom before the cruise, and a second transfer expanding at mesopelagic layers during the cruise. Regarding the deep carbon transfer efficiency, it appeared that above the plateau (A3 site) the mesopelagic remineralization was not a major barrier to the transfer of organic matter to the seafloor (close to 500 m). There, the efficiency of carbon transfer to the bottom waters (> 400 m) as assessed by PP, EP and MR fluxes comparisons reached up to 87 % of the carbon exported from the upper 150 m. In contrast, at the deeper locations, mesopelagic remineralization clearly limited the transfer of carbon to depths of > 400 m. For sites at the margin of the plateau (station E-4W) and the polar front (station F-L), mesopelagic remineralization even exceeded Published by Copernicus Publications on behalf of the European Geosciences Union. S. H. M. Jacquet et al.: Early season mesopelagic carbon remineralizationupper 150 m export, resulting in a zero transfer efficiency to depths > 800 m. In the polar front meander (time series), the capacity of the meander to transfer carbon to depth > 800 ...

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Effect of trace metal‐limited growth on the postmortem dissolution of the marine diatom Pseudo‐nitzschia delicatissima

Boutorh

Moriceau

Gallinari

et al. 2016

Global Biogeochemical Cycles

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We investigated the effects of iron (Fe) and copper (Cu) limitations on biogenic silica (bSiO2) dissolution kinetics of the marine diatom Pseudo‐nitzschia delicatissima during a 3 week batch dissolution experiment. The dissolution of this species was faster during the first week than thereafter. Modeling results from four dissolution models and scanning electron microcopy images suggested the successive dissolution of two phases of bSiO2, with two different dissolution constants. Micronutrient limitation during growth affected the respective proportion of the two phases and their dissolution constants. After 3 weeks of dissolution, frustules from micronutrient‐limited diatoms were better preserved than those of replete cells. Our results also confirm that micronutrient‐limited cells may export more Si relative to N than replete cells and may increase the silicate pump: This may not only be due to a higher degree of silicification of the live cells but also to a decoupling between the recycling of Si and N during dissolution. We suggest that a mechanistic understanding of the evolution of the dissolution constant during dissolution is needed. This would improve the parameterization of dissolution in ecosystem models, and ultimately their predictions on the amount of bSiO2 that dissolves in the photic zone, and the amount of bSiO2 that is exported to the seafloor.

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Seasonal evolution of net and regenerated silica production around a natural Fe-fertilized area in the Southern Ocean estimated with Si isotopic approaches

Cited by 47 publications

References 69 publications

Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

Early spring mesopelagic carbon remineralization and transfer efficiency in the naturally iron-fertilized Kerguelen area

Effect of trace metal‐limited growth on the postmortem dissolution of the marine diatom Pseudo‐nitzschia delicatissima

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