Polar <scp>F</scp>ront around the <scp>K</scp>erguelen <scp>I</scp>slands: An up‐to‐date determination and associated circulation of surface/subsurface waters

Park, Young‐Hyang; Durand, Isabelle; Kestenare, Élodie; Rougier, Gilles; Zhou, Meng; d’Ovidio, Francesco; Cotté, Cédric; Lee, Jae-Hak

doi:10.1002/2014jc010061

Cited by 118 publications

(182 citation statements)

References 25 publications

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“…Studies conducted during KEOPS1 showed a decoupling of the seasonal use of nitrate and silicic acid stocks over the Kerguelen Plateau (Mosseri et al, 2008), although Si : NO 3 assimilation ratios were close to 1, in accordance with what is expected for non-limiting iron conditions (Takeda, 1998; Park et al (2014). The inset picture gives indication about surface chl a (colour scale), surface velocity fields (arrows), and the polar front (PF, black line).…”

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

confidence: 70%

“…1). Moreover, a third condition impacting productivity is the proximity of the polar front, the trajectory of which is steered by the bottom topography (Park et al, 2014). Such a frontal system by itself offers peculiar conditions inducing significant biological activity (de Baar et al, 1995).…”

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

confidence: 99%

“…1): (i) over the south-eastern Kerguelen Plateau, remarkably constrained by the bathymetry, (ii) in a plume extending eastward through the interaction between the polar front jet, crossing the plateau in a narrow mid-depth channel just to the south of the Kerguelen Island, and the rise bordering the basin to the north, (iii) and to the easternmost part of the study area in a zone of retroflection of the polar front and of eddy mixing between Antarctic and subantarctic surface waters (see Park et al, 2014). This complex distribution is in agreement with an input of iron from the interaction between the iron-deficient Antarctic Circumpolar Current and the local bathymetry Sokolov and Rintoul, 2007).…”

Section: High Primary Production In Naturally Iron-fertilized Bloomsmentioning

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: 70%

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

confidence: 99%

Section: High Primary Production In Naturally Iron-fertilized Bloomsmentioning

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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“…Dissolved iron (dFe) is delivered to the mixed layer through two processes: winter mixing and entrainment of dFe from deeper waters and, to a less extend, vertical diapycnal diffusion of dFe in summer (Bowie et al, 2015). South of the Kerguelen Island, the polar front is permanent and non motile (Park et al, 2014) and therefore does not impact sediment trap deployment location. At the A3 station, the circulation is weak (o3 cm s À 1 ) and primarily tidal-driven (Park et al, 2008).…”

Section: Sediment Trap Deployment and Environmental Datamentioning

confidence: 99%

Planktic foraminifer and coccolith contribution to carbonate export fluxes over the central Kerguelen Plateau

Rembauville

Meilland

Ziveri

et al. 2016

Deep Sea Research Part I: Oceanographic Research Papers

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a b s t r a c tWe report the contribution of planktic foraminifers and coccoliths to the particulate inorganic carbon (PIC) export fluxes collected over an annual cycle (October 2011/September 2012) on the central Kerguelen Plateau in the Antarctic Zone (AAZ) south of the Polar Front (PF). The seasonality of PIC flux was decoupled from surface chlorophyll a concentration and particulate organic carbon (POC) fluxes and was characterized by a late summer (February) maximum. This peak was concomitant with the highest satellite-derived sea surface PIC and corresponded to a Emiliania huxleyi coccoliths export event that accounted for 85% of the annual PIC export. The foraminifer contribution to the annual PIC flux was much lower (15%) and dominated by Turborotalita quinqueloba and Neogloboquadrina pachyderma. Foraminifer export fluxes were closely related to the surface chlorophyll a concentration, suggesting food availability as an important factor regulating the foraminifer's biomass. We compared size-normalized test weight (SNW) of the foraminifers with previously published SNW from the Crozet Islands using the same methodology and found no significant difference in SNW between sites for a given species. However, the SNW was significantly species-specific with a threefold increase from T. quinqueloba to Globigerina bulloides. The annual PIC:POC molar ratio of 0.07 was close to the mean ratio for the global ocean and lead to a low carbonate counter pump effect ( $ 5%) compared to a previous study north of the PF (6-32%). We suggest that lowers counter pump effect south of the PF despite similar productivity levels is due to a dominance of coccoliths in the PIC fluxes and a difference in the foraminifers species assemblage with a predominance of polar species with lower SNW.

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“…Detailed descriptions of the complex physical structure of the area, circulation, water masses and fronts are given in Park et al (2014). Briefly, the main hydrodynamic features observed during the cruise are the following (see θ − S diagram, Fig.…”

Section: Study Areamentioning

confidence: 99%

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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Polar Front around the Kerguelen Islands: An up‐to‐date determination and associated circulation of surface/subsurface waters

Cited by 118 publications

References 25 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

Planktic foraminifer and coccolith contribution to carbonate export fluxes over the central Kerguelen Plateau

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

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