Iron budgets for three distinct biogeochemical sites around the Kerguelen archipelago (Southern Ocean) during the natural fertilisation experiment KEOPS-2

Bowie, Andrew R.; Merwe, Pier van der; Quéroué, Fabien; Trull, Thomas W.; Fourquez, Marion; Planchon, F.; Sarthou, Géraldine; Chever, Fanny; Townsend, Ashley T.; Obernosterer, Ingrid; Sallée, Jean‐Baptiste; Blain, S.

doi:10.5194/bgd-11-17861-2014

Cited by 33 publications

(40 citation statements)

References 127 publications

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“…Unexpectedly, the highest DWA Ba xs value of the whole study area (572 pM; 150-400 m) was observed at the reference R-2 site. For R-2, Bowie et al (2014), Quéroué et al (2015) and van der Merve et al (2015) reported local maxima in particulate and dissolved trace metals at 500 m and deeper, reflecting lateral transport of lithogenic matter possibly originating from the Leclaire Rise (a large seamount located west of R-2). Similarly, observed a maximum of lithogenic silica (LSi) at 500 m, confirming lithogenic inputs there.…”

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

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

confidence: 99%

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

et al. 2015

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“…At all stations, seawater was collected with 10 L Teflon-lined Niskin-1010X bottles mounted on a 1018 rosette system adapted for trace-metal clean work (Bowie et al, 2014). Sampling depths (surface mixed layer) were 40 m at stations R2 and E-4W, 37 m at station E-3 and 25 m at station E-5.…”

Section: Experimental Designmentioning

confidence: 99%

“…In situ samples for dissolved organic carbon (DOC) analyses were taken with Teflon-lined Niskin-1010X bottles adapted for trace-metal clean work (Bowie et al, 2014). Seawater was filtered through two combusted GF/F (0.7 µm nominal pore size, Whatman) filters and 15 mL of the filtrate was stored acidified (H 3 PO 4 , final pH = 2) in combusted 20 mL glass ampoules at room temperature in the dark.…”

Section: Dissolved Organic Carbon Analysesmentioning

confidence: 99%

Fe and C co-limitation of heterotrophic bacteria in the naturally fertilized region off the Kerguelen Islands

2015

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Abstract. It has been univocally shown that iron (Fe) is the primary limiting nutrient for phytoplankton metabolism in high-nutrient, low-chlorophyll (HNLC) waters, yet the question of how this trace metal affects heterotrophic microbial activity is far less understood. We investigated the role of Fe for bacterial heterotrophic production and growth at three contrasting sites in the naturally Fe-fertilized region east of the Kerguelen Islands and at one site in HNLC waters during the KEOPS2 (Kerguelen Ocean and Plateau Compared Study 2) cruise in spring 2011. We performed dark incubations of natural microbial communities amended either with iron (Fe, as FeCl 3 ) or carbon (C, as trace-metal clean glucose), or a combination of both, and followed bacterial abundance and heterotrophic production for up to 7 days. Our results show that single and combined additions of Fe and C stimulated bulk and cell-specific bacterial production at the Fe-fertilized sites, while in HNLC waters only combined additions resulted in significant increases in these parameters. Bacterial abundance was enhanced in two out of the three experiments performed in Fe-fertilized waters but did not respond to Fe or C additions in HNLC waters. Our results provide evidence that both Fe and C are present at limiting concentrations for bacterial heterotrophic activity in the naturally fertilized region off the Kerguelen Islands in spring, while bacteria were co-limited by these elements in HNLC waters. These results shed new light on the role of Fe in bacterial heterotrophic metabolism in regions of the Southern Ocean that receive variable Fe inputs.

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“…Seawater samples were collected with 10-L Niskin 1010X bottles set up on an autonomous model 1018 trace metal rosette especially adapted for trace metal work (General Oceanics Inc., USA; Bowie et al, 2014). Each Niskin bottle was acid-washed (2 % HCl) and rinsed with Milli-Q water before the rosette was deployed.…”

Section: Sampling and Manipulation Under Trace Metal Clean Conditionsmentioning

confidence: 99%

Microbial iron uptake in the naturally fertilized waters in the vicinity of the Kerguelen Islands: phytoplankton–bacteria interactions

et al. 2015

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Abstract. Iron (Fe) uptake by the microbial community and the contribution of three different size fractions was determined during spring phytoplankton blooms in the naturally Fe-fertilized area off the Kerguelen Islands (KEOPS2). Total Fe uptake in surface waters was on average 34 ± 6 pmol Fe L −1 d −1 , and microplankton (> 25 µm size fraction; 40-69 %) and pico-nanoplankton (0.8-25 µm size fraction; 29-59 %) were the main contributors. The contribution of heterotrophic bacteria (0.2-0.8 µm size fraction) to total Fe uptake was low at all stations (1-2 %). Iron uptake rates normalized to carbon biomass were highest for pico-nanoplankton above the Kerguelen Plateau and for microplankton in the downstream plume. We also investigated the potential competition between heterotrophic bacteria and phytoplankton for the access to Fe. Bacterial Fe uptake rates normalized to carbon biomass were highest in incubations with bacteria alone, and dropped in incubations containing other components of the microbial community. Interestingly, the decrease in bacterial Fe uptake rate (up to 26-fold) was most pronounced in incubations containing piconanoplankton and bacteria, while the bacterial Fe uptake was only reduced by 2-to 8-fold in incubations containing the whole community (bacteria + pico-nanoplankton + microplankton). In Fe-fertilized waters, the bacterial Fe uptake rates normalized to carbon biomass were positively correlated with primary production. Taken together, these results suggest that heterotrophic bacteria are outcompeted by small-sized phytoplankton cells for the access to Fe during the spring bloom development, most likely due to the limitation by organic matter. We conclude that the Fe and carbon cycles are tightly coupled and driven by a complex interplay of competition and synergy between different members of the microbial community.

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Iron budgets for three distinct biogeochemical sites around the Kerguelen archipelago (Southern Ocean) during the natural fertilisation experiment KEOPS-2

Abstract: International audienc

Cited by 33 publications

References 127 publications

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

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

Fe and C co-limitation of heterotrophic bacteria in the naturally fertilized region off the Kerguelen Islands

Microbial iron uptake in the naturally fertilized waters in the vicinity of the Kerguelen Islands: phytoplankton–bacteria interactions

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