Winter biogenic silica and diatom distributions in the Indian sector of the Southern Ocean

Weir, Ian; Fawcett, Sarah E.; Smith, S.; Walker, David; Bornman, Thomas G.; Fietz, Susanne

doi:10.1016/j.dsr.2020.103421

Cited by 18 publications

(26 citation statements)

References 106 publications

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“…Major nutrient concentrations have been reported previously (Weir et al, 2020). Here we briefly describe the distribution of PO 4 (Figure 2B and Supplementary Figure 2…”

Section: Dissolved Phosphatementioning

confidence: 68%

“…Seawater samples for macronutrient analysis were collected from GO-FLO bottles, filtered immediately after collection using a 0.2 µm pore size syringe filter (Anotop) into 50 mL Falcon R tubes and frozen at −20 • C. Post cruise, PO 4 was determined manually by colorimetric method (Grasshoff, 1983) at the Marine Biogeochemistry Laboratory at the University of Cape Town (MBL-UCT; Weir et al, 2020). The analytical error of the PO 4 measurements was ±0.06 µmol kg −1 (Weir et al, 2020).…”

Section: Phosphate (Po 4 ) Determinationmentioning

confidence: 99%

“…The transect intersected several frontal systems which, in turn, separated the study area into physically and biogeochemically distinct regions (Figure 1A). Frontal positions were determined previously (Weir et al, 2020) following temperature, salinity and oxygen criteria outlined in the literature (Orsi et al, 1995;Belkin and Gordon, 1996;Pollard et al, 2002…”

Section: Frontal Positionsmentioning

confidence: 99%

“…The SML at each station was defined as the depth interval between the sea surface and the Mixed Layer Depth (MLD) which was calculated as the depth (between 10 and 400 m) at which the Brunt Väisälä frequency (BVF) squared reaches a maximum while the euphotic zone depth was approximated as the depth at which 1% of surface PAR was measured (Weir et al, 2020…”

Section: Surface Mixed Layer (Sml) and Euphotic Depthmentioning

confidence: 99%

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Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

et al. 2021

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Winter distributions of dissolved cadmium (dCd) and particulate cadmium (pCd) were measured for the first time in the Indian sector of the Southern Ocean thereby contributing a unique spatial and seasonal dataset. Seven depth profiles, between 41°S and 58°S, were collected along the 30°E longitude during the 2017 austral winter to investigate the biogeochemical cycling of cadmium during a period characterized by contrasting upper water column dynamics compared to summer. Our results support an important role for biological uptake during winter months albeit weaker compared to summer. Distinct, biologically driven changes in cadmium cycling across the transect were observed. For example, surface ratios of pCd to phosphorus (P; pCd:P) increased from 0.37 to 1.07 mmol mol–1 between the subtropical zone (STZ) and the Antarctic zone (AAZ) reflecting increased Cd requirements for diatoms at higher latitudes which, in turn, was driven by a complex relationship between the availability of dCd and dissolved iron (dFe), zinc (dZn) and manganese (dMn). Vertical profiles of pCd:P displayed near-surface maxima consistent with (1) P occurring in two phases with different labilities and the lability of Cd being somewhere in-between and (2) increasing dCd to phosphate (PO4; dCd:PO4) ratios with depth at each station. North of the Antarctic Polar Front (APF), a secondary, deeper pCd:P maximum may reflect an advective signal associated with northward subducting Antarctic Intermediate Water (AAIW). The strong southward increase in surface dCd and dCd:PO4, from approximately 10–700 pmol kg–1 and 40–400 μmol mol–1, respectively, reflected the net effect of preferential uptake and regeneration of diatoms with high Cd content and the upwelling of Cd enriched water masses in the AAZ. Furthermore, distinct dCd versus PO4 relationships were observed in each of the intermediate and deep water masses suggesting that dCd and PO4 distributions at depth are largely the result of physical water mass mixing.

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“…Major nutrient concentrations have been reported previously (Weir et al, 2020). Here we briefly describe the distribution of PO 4 (Figure 2B and Supplementary Figure 2…”

Section: Dissolved Phosphatementioning

confidence: 68%

Section: Phosphate (Po 4 ) Determinationmentioning

confidence: 99%

Section: Frontal Positionsmentioning

confidence: 99%

Section: Surface Mixed Layer (Sml) and Euphotic Depthmentioning

confidence: 99%

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Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

et al. 2021

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“…strong correlation with NH₄⁺ concentration south of the SAF (r = 0.65). In the nano+ size class, NO uptake was likely driven in the SAZ by dinoflagellates and some nanoeukaryotes, and in the PFZ and AZ by diatoms, which remain active in these zones in winter (Weir et al, 2020). By contrast, nanoeukaryotes, which have a higher per-cell nutrient requirement than the equally-abundant picoeukaryotes, may have dominated NH₄⁺ uptake in the PFZ and AZ given that higher nanoeukaryote abundances corresponded with lower NH₄⁺ concentrations at a number of stations (e.g., stations 50.0°S, 51.1°S, and 55.5°S; Fig.…”

Section: Ammonium Consumptionmentioning

confidence: 99%

Biogeochemical controls on wintertime ammonium accumulation in the surface layer of the Southern Ocean

Smith

Altieri

Mdutyana

et al. 2021

Preprint

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Abstract. The production and consumption of ammonium (NH4+) are essential upper-ocean nitrogen cycle pathways, yet in the Southern Ocean where NH4+ has been observed to accumulate in surface waters, its mixed-layer cycling remains poorly understood. For surface samples collected between Cape Town and the marginal ice zone (MIZ) in winter 2017, we found that NH4+ concentrations were five-fold higher than is typical for summer, and lower north than south of the Subantarctic Front (SAF; 0.01–0.26 µM versus 0.19–0.70 µM). Our observations confirm that NH4+ accumulates in the Southern Ocean’s winter mixed layer, particularly in polar waters. NH4+ uptake rates were highest near the Polar Front (PF; 12.9 ± 0.4 nM day−1) and in the Subantarctic Zone (10.0 ± 1.5 nM day−1), decreasing towards the MIZ (3.0 ± 0.8 nM day−1) despite high ambient NH4+ concentrations, likely due to low sea surface temperatures and light availability. By contrast, rates of NH4+ oxidation were higher south than north of the PF (16.0 ± 0.8 versus 11.1 ± 0.5 nM day−1), perhaps due to the lower light and higher iron conditions characteristic of polar waters. Augmenting our dataset with NH4+ concentration measurements spanning the 2018/2019 annual cycle reveals that mixed-layer NH4+ accumulation south of the SAF likely derives from sustained heterotrophic NH4+ production in late summer through winter that outpaces NH4+ consumption by temperature-, light, and iron-limited microorganisms. Our observations thus imply that the Southern Ocean becomes a biological source of CO2 to the atmosphere for half the year not only because nitrate drawdown is weak, but also because the ambient conditions favour net heterotrophy and NH4+ accumulation.

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The kinetics of ammonium uptake and oxidation across the Southern Ocean

Mdutyana

Sun

Burger

et al. 2022

Limnology & Oceanography

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Winter biogenic silica and diatom distributions in the Indian sector of the Southern Ocean

Cited by 18 publications

References 106 publications

Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

Biogeochemical controls on wintertime ammonium accumulation in the surface layer of the Southern Ocean

The kinetics of ammonium uptake and oxidation across the Southern Ocean

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