KERFIX, a time-series station in the Southern Ocean: a presentation

Jeandel, Catherine; Ruiz‐Pino, Diana; Gjata, Elvis; Poisson, Alain; Brunet, Christian; Charriaud, Edwige; Dehairs, Frank; Delille, Daniel; Fiala, Michel; Fravalo, Charles; Miquel, Juan Carlos; Park, Young‐Hyang; Pondaven, Philippe; Quéguiner, Bernard; Razouls, Suzanne; Shauer, Bernard; Tréguer, Paul

doi:10.1016/s0924-7963(98)00064-5

Cited by 62 publications

(34 citation statements)

References 21 publications

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“…Station R-2, located south of the PF, also displays a young apparent age. At station Kerfix located close to station R-2, Jeandel et al (1998) reported westward currents associated with a recirculation pattern that may transport chemical elements originating from the Kerguelen Plateau. The Ra signal may then be transported eastward, as suggested by the significant 223 Ra activities also observed east of station R-2, south of the PF (Figs.…”

Section: Timescales Of the Offshore Transport Of Surface Watersmentioning

confidence: 95%

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

et al. 2015

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Abstract. The Southern Ocean is known to be the largest high-nutrient, low-chlorophyll (HNLC) region of the global ocean due to iron limitation. However, a large phytoplankton bloom develops annually downstream of the Kerguelen Islands, a bloom which is sustained partly by iron released from the sediments deposited onto the shelves. In the framework of the KEOPS-2 project, we used radium isotopes ( 224 Ra, T 1/2 = 3.66 d; 223 Ra, T 1/2 = 11.4 d; 228 Ra, T 1/2 = 5.75 yr) to provide information on the origin of iron fertilization and on the timescales of the transfer of sedimentderived inputs (including iron and other micronutrients) towards offshore waters. Significant 224 Ra and 223 Ra activities were found in the near vicinity of the Kerguelen Islands, in agreement with the short half-lives of these isotopes. Significant 224 Ra and 223 Ra activities were also detected up to 200 km downstream of the islands and more unexpectedly in offshore waters south of the polar front. These observations thus clearly indicate (i) that the sediment-derived inputs are rapidly transferred towards offshore waters (on timescales on the order of several days up to several weeks) and (ii) that the polar front is not a physical barrier for the chemical elements released from the sediments of the Kerguelen Plateau. The Ra data set suggests that iron and other micronutrients released by the shelves of the Kerguelen Islands may contribute to fueling the phytoplankton bloom downstream of the islands, despite the presence of the polar front. However, the heterogeneous distribution of the 224 Ra and 223 Ra activities in surface waters suggests that this supply across the front is not a continuous process but rather a process that is highly variable in space and time.

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Section: Timescales Of the Offshore Transport Of Surface Watersmentioning

confidence: 95%

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

et al. 2015

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“…In the model, the biomass of chlorophyll a, Chl a t , was calculated from the BSi concentration using the molar ratios Si : N of 4 : 1 (a typical value for the Southern Ocean (Pondaven et al, 1998), especially given the heavy silicification of diatoms like Fragilariopsis kerguelensis) and C : N of 106 : 16 (the Redfield ratio), and a mass ratio of C : Chlorophyll of 80 : 1 (Chan, 1980) as follows:…”

Section: Equations For Change In Concentrations Of Dsi and Bsimentioning

confidence: 99%

Exploring interacting influences on the silicon isotopic composition of the surface ocean: a case study from the Kerguelen Plateau

2014

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Abstract. This study presents six new water column profiles of the silicon isotopic composition (δ 30 Si) of dissolved silicon (DSi) from the Atlantic and Indian sectors of the Southern Ocean and a variable depth box model of silica cycling in the mixed layer that was constructed to illuminate the evolution of surface ocean δ 30 Si over the full course of a year. In keeping with previous observations, δ 30 Si values ranged from +1.9 to +2.4 ‰ in the mixed layer (ML), +1.2 to +1.7 ‰ in Winter Water (WW), and +0.9 to +1.4 ‰ in Circumpolar Deep Water (CDW). These data also confirmed the occurrence of diminished values for ML δ 30 Si at low DSi concentrations in early austral autumn on the Kerguelen Plateau. The box model was used to investigate whether these low, post-growing season values of δ 30 Si were related to input of DSi to the ML from basalt weathering, biogenic silica dissolution (with or without isotopic fractionation), the onset of winter mixing, or some combination of the three. Basalt weathering and fractionation during biogenic silica dissolution could both lower ML δ 30 Si below what would be expected from the extent of biological uptake of DSi. However, the key driver of the early autumn decrease in δ 30 Si appears to be the switch from bloom growth (with net removal of DSi and net accumulation of biogenic silica (BSi) biomass) to steady state growth (when slow but continuing production of BSi prevented significant net increase in DSi concentrations with diffusive input of DSi from WW but not decrease in ML δ 30 Si towards WW values). Model results also indicated that fractionation during dissolution has only a negligible effect on the δ 30 Si of BSi exported throughout the course of the year. However, seasonal changes in export efficiency (e.g. favouring the export of bloom BSi versus the export of BSi produced during other times of the year) should strongly influence the δ 30 Si of BSi accumulating in marine sediments.Finally, the choice for the parameterisation of the mixing between the ML and the WW in terms of δ 30 Si (i.e. constant or allowed to vary with the seasonal migration of the thermocline) is critical to take into account in box model simulations of the silica biogeochemical cycle. Altogether, these results suggest that as a paleoceanographic proxy, δ 30 Si may more reflect the dominant mode of production of the BSi that is exported (i.e. bloom versus steady state growth) rather than strictly the extent of DSi utilisation by diatoms.

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“…To study the temporal stability (or variability) of the oceanic properties below the mixed layer, the first 1000 m of the water column is sampled at each station. Three additional full‐depth stations are obtained; one in the subtropical region (4500 m for station 17 at 30°S–66°E), one situated south of the Polar Front (PF, 1650 m for station 10 at 50°40′S, also known as Kerfix/JGOFS time series station [ Jeandel et al , 1998]), and one in the Southern Ocean (4750 m for station 11 at 56°30′S–63°E). The deep samples are also used to check the accuracy of the measurements from cruise to cruise.…”

Section: Data Collections During Océan Indien Service D'observations mentioning

confidence: 99%

“…To estimate the magnitude of anomalies for the period of our cruises, we computed the monthly SST anomalies from 1982 to 2000 at location 50.5°S–68.5°E (Figure 4), which is the position of one of our hydrocast stations in the POOZ (OISO st‐10). The station is known as KERFIX/JGOFS time series station, which was operating in 1990–1995 [ Jeandel et al , 1998]. In this region, SST varies from about 2°C in winter to 4.5°C in summer.…”

Section: Large‐scale Distribution Of Co2 Sources and Sinks In Australmentioning

confidence: 99%

Interannual variability of the carbon dioxide system in the southern Indian Ocean (20°S–60°S): The impact of a warm anomaly in austral summer 1998

Jabaud-Jan

Metzl

Brunet

et al. 2004

Global Biogeochemical Cycles

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The interannual variations of the carbon dioxide system and air‐sea CO2 fluxes are analyzed in the southwestern Indian Ocean from both in situ (Océan Indien Service d'Observations cruises in 1998 and 2000) and simulated oceanic CO2 fugacity dissolved inorganic carbon, total alkalinity, and nutrients. During austral summer of 1998, the ocean was warmer from 20°S to 60°S. In the Subtropical Zone (20°S–37°S), the warming, associated with the subtropical dipole pattern, creates an oceanic CO2 source around 2 mmol m−2 d−1 in January 1998 where all previous observations, included in 2000, indicated that this region was a small sink in summer. In the Sub‐Antarctic and Polar Front Zones (37°S–50°S), the interannual signal is not clearly detected because of the complex coupling between the horizontal and vertical dynamics and the biological activity that creates very high mesoscale variability in each summer. For the austral region, south of the Polar Front, we observe large variability in the CO2 sources and sinks between summer 1998 and 2000. In the Seasonal Ice Zone (south of 58°S) the interannual variation of the CO2 flux was mainly controlled by a warmer ocean, from 1.1°C, in summer 1998 (CO2 source of 3.2 mmol m−2 d−1) and an enhanced primary production occurring during summer 2000 (CO2 sink of −3.8 mmol m−2 d−1). In the Permanent Open Ocean Zone (POOZ, latitude 50°S–57°S), despite the half‐degree warmer sea surface in 1998, we observe lower (−15 μatm (1 atm = 105 × 1.01325 N m−2) on average) during this period, and consequently, we estimate a double of the oceanic CO2 sink in this region in 1998 than 2000, from −3.2 mmol m−2 d−1 in 1998 to −1.3 mmol m−2 d−1 in 2000. The strong oceanic CO2 sink in 1998 is associated with a dramatic decrease of nutrients (silicates less than 2 μmol kg−1). The enhanced biological activity in summer 1998, probably diatoms bloom, is also apparent in Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) chlorophyll a estimates. Using a one‐dimensional biogeochemical model applied in the POOZ and SeaWIFS time series, we predict a stronger oceanic sink during summer season than the winter, which is contrary to previous studies. The model suggests that biological activity controls most of the sink anomaly in summer 1998 (for about 70%) and dominates the warming effect.

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KERFIX, a time-series station in the Southern Ocean: a presentation

Cited by 62 publications

References 21 publications

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

Exploring interacting influences on the silicon isotopic composition of the surface ocean: a case study from the Kerguelen Plateau

Interannual variability of the carbon dioxide system in the southern Indian Ocean (20°S–60°S): The impact of a warm anomaly in austral summer 1998

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