Influence of biotic factors on the hydrochemical structure of surface water in the Polar Frontal Zone of the Atlantic Antarctic

Dafner, Evgeny V.; Mordasova, N. V.

doi:10.1016/0304-4203(94)90098-1

Cited by 27 publications

(23 citation statements)

References 9 publications

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“…3a) (Dafner and Mordasova, 1994;Brzezinski et al, 2001;Varela et al, 2004;De La Rocha et al, 2011). As also expected based on previous studies (Brzezinski et al, 2001;Varela et al, 2004;Cardinal et al, 2005;Fripiat et al, 2011c), the isotopic composition of DSi (δ 30 Si DSi ) generally increased with decreasing DSi concentration, both at the surface (Fig.…”

Section: Concentration and δ 30 Si Of Dsi And Bsi On The Kerguelen Plsupporting

confidence: 88%

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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Section: Concentration and δ 30 Si Of Dsi And Bsi On The Kerguelen Plsupporting

confidence: 88%

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

2014

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“…Between the SACCF and the Antarctic Polar Front (APF) to the north there exists the most intense and most geographically extensive meridional gradient in mixed-layer silicic acid concentration in the global ocean (Pondaven et al 2000;Smith et al 2000). The gradient can be as steep as 0.5 mol L Ϫ1 km Ϫ1 across, which [Si(OH) 4 ] changes by over 40 mol L Ϫ1 (Dafner and Mordasova 1994;Smith et al 2000). Near-total silicic acid depletion (Ͻ1 mol L Ϫ1 ) can occur in this zone during austral summer while nitrate remains Ͼ20 mol L Ϫ1 (Sigmon et al 2002), resulting in a seasonal shift from HNLC to LSiHNLC conditions.…”

Section: Acknowledgmentsmentioning

confidence: 99%

Control of silica production by iron and silicic acid during the Southern Ocean Iron Experiment (SOFeX)

Brzezinski

Jones

Demarest

2005

Limnology & Oceanography

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We examined the role of Si limitation in mediating the response of siliceous biomass and silica production to mesoscale Fe fertilization in the high-silicic acid high-nitrate waters of the Antarctic and in the low-silicic acid high-nitrate waters of the Subantarctic during austral summer. Iron fertilization stimulated biogenic silica production and silicic acid depletion in both regions. Si limitation significantly curtailed the response of silica production to Fe in the Subantarctic, but not in the Antarctic. Additions of silicic acid to Fe-enriched waters of the Subantarctic more than doubled specific silica production rates beyond the increase caused by Fe alone. This result, combined with the presence of Si limitation both inside and outside of the fertilized patch in the Subantarctic, indicates that silica production in the Subantarctic is regulated by both Fe and Si during austral summer. Fe increased the ability of Subantarctic diatom assemblages to take up low concentrations of Si over an order of magnitude by increasing maximum uptake rates and lowering half-saturation constants for silicic acid uptake. Our observations indicate that the dramatic gradient in Si availability across the Antarctic Circumpolar Current exerts a strong control on the contribution of diatoms to new production following Fe enrichment in the Southern Ocean during austral summer. With sufficient Fe to allow nitrate depletion, the abundant silicic acid in the Antarctic would allow diatoms to dominate nitrate use; however, low silicic acid concentrations in the Subantarctic would restrict the fraction of available nitrate that would be consumed by diatoms to ca. 5%.

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“…Phytoplankton blooms associated with the PF are typically dominated by larger diatom species (Lutjeharms et al, 1985;Laubscher et al, 1993;Dafner and Mordosova, 1994;Jochem et al, 1995;de Baar et al, 1995;Smetacek et al, 1997;Brown and Landry, 2001). Smaller phytoplankton species experience strong grazing pressure by microzooplankton.…”

Section: Introductionmentioning

confidence: 99%

“…Olson et al (1994) argued that the secondary circulation and local eddy field associated with meanders play key roles in frontal biological enhancement. Dafner and Mordosova (1994) also stressed the role of eddy pumping as a source of nutrients. Meander-induced upwelling and eddy formation are likely intensified where Southern Ocean fronts interact with large topographic features (Moore et al, 1999a,b;.…”

Section: Introductionmentioning

confidence: 99%

Surface chlorophyll concentrations in relation to the Antarctic Polar Front: seasonal and spatial patterns from satellite observations

Moore

Abbott

2002

Journal of Marine Systems

150

118

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Satellite ocean color data from the Sea Viewing Wide Field of View Sensor (SeaWiFS) are used to investigate phytoplankton bloom dynamics at the Antarctic Polar Front (PF). Satellite sea surface temperature (SST) data are used to map the location of the PF at weekly timescales. Elevated chlorophyll within the PF often appears as a narrow band that occupies only a portion of the SST gradient across the PF. Phytoplankton blooms within the PF occur most frequently during the month of December and are unevenly distributed within the Southern Ocean. Elevated chlorophyll concentrations at the PF are most frequently observed where the current is interacting with large topographic features.Mesoscale physical processes, including meander-induced upwelling and increased eddy mixing, where the PF encounters large topographic features likely leads to increased nutrient flux to surface waters in these regions. The highest mean chlorophyll values associated with the PF occur where the front comes into contact with relatively shallow waters along the North Scotia Ridge and at Kerguelen Plateau. Iron input from sedimentary sources likely plays an important role in these regions.Over seasonal timescales it appears likely that light-limitation prevents phytoplankton blooms at the PF during winter and spring months. PF blooms are observed most commonly during December when surface radiation peaks and mixed layer depths are rapidly shoaling. Even during December, when the light regime would seem to be favorable, PF blooms are largely restricted to regions where enhanced nutrient fluxes to surface waters due to frontal dynamics are likely. During late summer, nutrient limitation due to depletion of iron and possibly silicate largely prevent blooms at the PF. In the fall, deepening mixed layers would provide some relief from nutrient limitation but likely lead again to light-limitation of growth rates and the prevention of blooms. D

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Influence of biotic factors on the hydrochemical structure of surface water in the Polar Frontal Zone of the Atlantic Antarctic

Cited by 27 publications

References 9 publications

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

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

Control of silica production by iron and silicic acid during the Southern Ocean Iron Experiment (SOFeX)

Surface chlorophyll concentrations in relation to the Antarctic Polar Front: seasonal and spatial patterns from satellite observations

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