High variability of dissolved iron concentrations in the vicinity of Kerguelen Island (Southern Ocean)

Quéroué, Fabien; Sarthou, Géraldine; Planquette, Hélène; Bucciarelli, Eva; Chever, Fanny; Merwe, Pier van der; Lannuzel, Delphine; Townsend, Ashley T.; Cheize, Marie; Blain, S.; d’Ovidio, Francesco; Bowie, Andrew R.

doi:10.5194/bgd-12-231-2015

Cited by 26 publications

(34 citation statements)

References 63 publications

(87 reference statements)

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“…5) due to high pFe and pAl supply over the Kerguelen Plateau that is relatively deficient in pMn, such as would be found in glacial runoff that has a signature which reflects fresh weathering of basaltic rocks (Doucet et al, 2005). This source theory is supported by the observation of high dissolved Mn (dMn) near the Leclaire Rise (Quéroué et al, 2015) and uniquely high pMn : pFe in sediments found below station R-2 (Table 2). Surface water particulate trace metals also reveal distinct differences.…”

Section: Elemental Ratios At Stations R-2 F-l and A3supporting

confidence: 67%

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Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

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Abstract. The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upstream high-nutrient, low-chlorophyll (HNLC), deep water (2500 m), reference station to compare with a shallow (500 m), strongly fertilised plateau station and continued the observations to a downstream, bathymetrically trapped recirculation of the Polar Front where eddies commonly form and persist for hundreds of kilometres into the Southern Ocean. Over the Kerguelen Plateau, mean particulate (1-53 µm) Fe and Al concentrations (pFe = 13.4 nM, pAl = 25.2 nM) were more than 20-fold higher than at an offshore (lower-productivity) reference station (pFe = 0.53 nM, pAl = 0.83 nM). In comparison, over the plateau dissolved Fe levels were only elevated by a factor of ∼ 2. Over the Kerguelen Plateau, ratios of pMn / pAl and pFe / pAl resemble basalt, likely originating from glacial/fluvial inputs into shallow coastal waters. In downstream, offshore deep-waters, higher pFe / pAl, and pMn / pAl ratios were observed, suggesting loss of lithogenic material accompanied by retention of pFe and pMn. Biological uptake of dissolved Fe and Mn and conversion into the biogenic particulate fraction or aggregation of particulate metals onto bioaggregates also increased these ratios further in surface waters as the bloom developed within the recirculation structure. While resuspension of shelf sediments is likely to be one of the important mechanisms of Fe fertilisation over the plateau, fluvial and glacial sources appear to be important to areas downstream of the island. Vertical profiles within an offshore recirculation feature associated with the Polar Front show pFe Published by Copernicus Publications on behalf of the European Geosciences Union. P. van der Merwe et al.: Kerguelen Plateau: particulate trace metal sourcesand pMn levels that were 6-fold and 3.5-fold lower, respectively, than over the plateau in surface waters, though still 3.6-fold and 1.7-fold higher respectively than the reference station. Within the recirculation feature, strong depletions of pFe and pMn were observed in the remnant winter water (temperature-minimum) layer near 175 m, with higher values above and below this depth. The correspondence between the pFe minima and the winter water temperature minima implies a seasonal cycle is involved in the supply of pFe into the fertilised region. This observed association is indicative of reduced supply in winter, which is counterintuitive if sediment resuspension and entrainment within the mixed layer is the primary fertilising mechanism to the downstream recirculation structure. Therefore, we hypothesise that lateral transport of pFe from shallow coastal waters is strong in spring, associated with snow melt and increased runoff due to rainfall, drawdown through summer and reduced supply in winter when snowfal...

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Section: Elemental Ratios At Stations R-2 F-l and A3supporting

confidence: 67%

“…Trace metal analysis of suspended particles, underlying sediment and settling particulate material will elucidate the source to sink progression of the particulate Fe pool. Following on from this work, and together with dissolved Fe measurements (Quéroué et al, 2015), a focused Fe budget will be constructed .…”

Section: Introductionmentioning

confidence: 99%

Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

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“…4b) and coincided with a slight increase in nutrients. There a deep Fe-enriched and lithogenic silica reservoir seemed to influence the area Quéroué et al, 2015). O 2 distribution was similar to that observed in the TEW.…”

Section: Biogeochemical Variablessupporting

confidence: 57%

Dissolved greenhouse gases (nitrous oxide and methane) associated with the naturally iron-fertilized Kerguelen region (KEOPS 2 cruise) in the Southern Ocean

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Abstract. The concentrations of greenhouse gases (GHGs), such as nitrous oxide (N 2 O) and methane (CH 4 ), were measured in the Kerguelen Plateau region (KPR). The KPR is affected by an annual microalgal bloom caused by natural iron fertilization, and this may stimulate the microbes involved in GHG cycling. This study was carried out during the KEOPS 2 cruise during the austral spring of 2011. Oceanographic variables, including N 2 O and CH 4 , were sampled (from the surface to 500 m depth) in two transects along and across the KRP, the north-south (TNS) transect (46 • -51 • S, ∼ 72 • E) and the east-west (TEW) transect (66 • -75 • E, ∼ 48.3 • S), both associated with the presence of a plateau, polar front (PF) and other mesoscale features. The TEW presented N 2 O levels ranging from equilibrium (105 %) to slightly supersaturated (120 %) with respect to the atmosphere, whereas CH 4 levels fluctuated dramatically, being highly supersaturated (120-970 %) in areas close to the coastal waters of the Kerguelen Islands and in the PF. The TNS showed a more homogenous distribution for both gases, with N 2 O and CH 4 levels ranging from 88 to 171 % and 45 to 666 % saturation, respectively. Surface CH 4 peaked at southeastern stations of the KPR (A3 stations), where a phytoplankton bloom was observed. Both gases responded significantly, but in contrasting ways (CH 4 accumulation and N 2 O depletion), to the patchy distribution of chlorophyll a. This seems to be associated to the supply of iron from various sources. Air-sea fluxes for N 2 O (from −10.5 to 8.65, mean 1.25 ± 4.04 µmol m −2 d −1 ) and for CH 4 (from 0.32 to 38.1, mean 10.01 ± 9.97 µmol −2 d −1 ) indicated that the KPR is both a sink and a source for N 2 O, as well as a considerable and variable source of CH 4 . This appears to be associated with biological factors, as well as the transport of water masses enriched with Fe and CH 4 from the coastal area of the Kerguelen Islands. These previously unreported results for the Southern Ocean suggest an intense microbial CH 4 production in the study area.

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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%

“…The R-2 HNLC reference station (white dot in Fig. 1b) is characterized by a very low biomass (with low iron contents; Quéroué et al, 2015). Stations TEW-3 and TNS-8 (black dots) are characterized by low to moderate biomass and Fe contents.…”

Section: Study Areamentioning

confidence: 99%

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

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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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High variability of dissolved iron concentrations in the vicinity of Kerguelen Island (Southern Ocean)

Cited by 26 publications

References 63 publications

Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

Dissolved greenhouse gases (nitrous oxide and methane) associated with the naturally iron-fertilized Kerguelen region (KEOPS 2 cruise) in the Southern Ocean

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

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