Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer

Joubert, WR; Thomalla, S.; Waldron, H. N.; Lucas, Michael I.; Boyé, Marie; Moigne, F.A Le; Planchon, F.; Speich, Sabrina

doi:10.5194/bg-8-2947-2011

Cited by 34 publications

(52 citation statements)

References 71 publications

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“…Furthermore, the radionuclides derived export production (e.g. 234 Th / 238 U) showed that the transfer rate of carbon to the mesopelagic zone was quite low in this domain (Planchon et al, 2012), consistent with a low new production (Joubert et al, 2011), and probably leading to the relative accumulation of particulate organic N and C observed in the subtropical region (Fig. 5).…”

Section: Biogeochemical Features Of the Subtropical Domain And Its Comentioning

confidence: 61%

“…It is likely that the ammonium which is kept at low value here was rapidly taken up. Oligotrophic conditions were further supported by 15 N incubation experiments which showed that the new production rate was low in this domain, unlike the regenerated production, as exemplified by a f-ratio of 0.24 compared to f-ratios of 0.41-0.49 south of this domain (Joubert et al, 2011). PIC and BSi concentrations were extremely low in this area, indicating that the biomass resulted from non-mineralizing phytoplankton.…”

Section: Biogeochemical Features Of the Subtropical Domain And Its Comentioning

confidence: 80%

“…Those later terms were not estimated during the cruise and not considered in our estimates, but they can represent 40 % of NO − 3 (Pondaven et al, 2000). The fraction of total nitrogen production sustained by ammonium or urea was deduced from shipboard determination of f-ratio (Joubert et al, 2011), where mean f-ratio characterizing each domain was used in our calculation.…”

Section: Daily Production Ratementioning

confidence: 99%

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Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

et al. 2013

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Abstract. Meridional and vertical distributions of several biogeochemical parameters were studied along a section in the southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer 2008 of the International Polar Year to characterize the biogeochemical provinces and to assess the seasonal net diatom production. Based on analyses of macro-nutrients, ammonium (NH 4 ), chlorophyll a, (Chl a), phaeopigments, biogenic silica (BSi), particulate inorganic carbon (PIC), and particulate organic carbon and nitrogen (POC and PON, respectively), four biogeochemical domains were distinguished along the section: the subtropical Atlantic, the confluence zone of the subtropical and subantarctic domains, the Polar Frontal Zone (PFZ) in the Antarctic Circumpolar Current (ACC), and the north-eastern branch of the Weddell Gyre. The subtropical region displayed extremely low nutrient concentrations featuring oligotrophic conditions, and sub-surface maxima of Chl a and phaeopigments never exceeded 0.5 µg L −1 and 0.25 µg L −1 , respectively. The anticyclonic and cyclonic eddies crossed in the Cape Basin were characterized by a deepening and a rise, respectively, of the nutrients isoclines. The confluence zone of the subtropical domain and the northern side of the ACC within the subantarctic domain displayed remnant nitrate and phosphate levels, whereas silicate concentrations kept to extremely low levels. In this area, Chl a level of 0.4-0.5 µg L −1 distributed homogenously within the mixed layer, and POC and PON accumulated to values up to 10 µM and 1.5 µM, respectively, indicative of biomass accumulation along the confluence zone during the late productive period. In the ACC domain, the Polar Frontal Zone was marked by a post-bloom of diatoms that extended beyond the Polar Front (PF) during this late summer condition, as primarily evidenced by the massive depletion of silicic acid in the surface waters. The accumulation of NH 4 to values up to 1.25 µM at 100 m depth centred on the PF and the accumulation of BSi up to 0.5 µM in the surface waters of the central part of the PFZ also featured a late stage of the seasonal diatom bloom. The silica daily net production rate based on the seasonal depletion of silicic acid was estimated to be 11.9 ± 6.5 mmol m −2 d −1 in the domain of the vast diatom post-bloom, agreeing well with the previously recorded values in this province. The Weddell Gyre occasionally displayed relative surface depletion of silicic acid, suggesting a late stage of a relatively minor diatom bloom possibly driven by iceberg drifting releases of iron. In this domain the estimated range of silica daily net production rate (e.g. 21.1 ± 8.8 mmol m −2 d −1 ) is consistent with previous studies, but was not significantly higher than that in the Polar Front region.

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Section: Biogeochemical Features Of the Subtropical Domain And Its Comentioning

confidence: 61%

Section: Biogeochemical Features Of the Subtropical Domain And Its Comentioning

confidence: 80%

Section: Daily Production Ratementioning

confidence: 99%

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Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

et al. 2013

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“…were the most abundant phytoplankton groups in the subtropical domain (Beker and Boye, 2010). This domain also featured oligotrophic conditions (Le Moigne et al, 2012) and relatively high regenerated production (Joubert et al, 2011), which leads us to think that cyanobacteria may also have been present. Cyanobacteria are often too small to be recognized clearly in light-microscope studies.…”

Section: Cycle Of the Organic Ligands Along The Sectionmentioning

confidence: 99%

New insights on the role of organic speciation in the biogeochemical cycle of dissolved cobalt in the southeastern Atlantic and the Southern Ocean

2012

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Abstract. The organic speciation of dissolved cobalt (DCo) was investigated in the subtropical region of the southeastern Atlantic, and in the Southern Ocean in the Antarctic Circumpolar Current (ACC) and the northern Weddell Gyre, between 34°25´ S and 57°33´ S along the Greenwich Meridian during the austral summer of 2008. The organic speciation of dissolved cobalt was determined by competing ligand exchange adsorptive cathodic stripping voltammetry (CLE-AdCSV) using nioxime as a competing ligand. The concentrations of the organic ligands (L) ranged between 26 and 73 pM, and the conditional stability constants (log K'CoL) of the organic complexes of Co between 17.9 and 20.1. Most dissolved cobalt was organically complexed in the water-column (60 to >99.9%). There were clear vertical and meridional patterns in the distribution of L and the organic speciation of DCo along the section. These patterns suggest a biological source of the organic ligands in the surface waters of the subtropical domain and northern subantarctic region, potentially driven by the cyanobacteria, and a removal of the organic Co by direct or indirect biological uptake. The highest L:DCo ratio (5.81 ± 1.07 pM pM−1) observed in these surface waters reflected the combined effects of ligand production and DCo consumption. As a result of these combined effects, the calculated concentrations of inorganic Co ([Co']) were very low in the subtropical and subantarctic surface waters, generally between 10−19 and 10−17 M. In intermediate and deep waters, the South African margins can be a source of organic ligands, as it was suggested to be for DCo (Bown et al., 2011), although a significant portion of DCo (up to 15%) can be stabilized and transported as inorganic species in those DCo-enriched water-masses. Contrastingly, the distribution of L does not suggest an intense biological production of L around the Antarctic Polar Front where a diatom bloom had recently occurred. Here [Co'] can be several orders of magnitude higher than those reported in the subtropical domain, suggesting that cobalt limitation was unlikely in the ACC domain. The almost invariant L:DCo ratio of ~1 recorded in these surface waters also reflected the conservative behaviours of both L and DCo. In deeper waters higher ligand concentrations were observed in waters previously identified as DCo sources (Bown et al., 2011). At those depths the eastward increase of DCo from the Drake Passage to the Greenwich Meridian could be associated with a large scale transport and remineralisation of DCo as organic complexes; here, the fraction stabilized as inorganic Co was also significant (up to 25%) in the low oxygenated Upper Circumpolar Deep Waters. Organic speciation may thus be a central factor in the biogeochemical cycle of DCo in those areas, playing a major role in the bioavailability and the geochemistry of Co.

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“…The PlankTOM10.2 biogeochemical model coupled with the two N 2 O submodels is incorporated into the ocean general circulation model NEMO v3.1 (Madec, 2008) Simulations were run to 2014, forced with daily atmospheric conditions from the NCEP reanalysis (Kalnay et al, 1996; for details see Buitenhuis et al, 2013a). Results are reported averaged over the last 5 years.…”

Section: N 2 O Productionmentioning

confidence: 99%

Constraints on global oceanic emissions of N<sub>2</sub>O from observations and models

2018

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Abstract. We estimate the global ocean N 2 O flux to the atmosphere and its confidence interval using a statistical method based on model perturbation simulations and their fit to a database of pN 2 O (n = 6136). We evaluate two submodels of N 2 O production. The first submodel splits N 2 O production into oxic and hypoxic pathways following previous publications. The second submodel explicitly represents the redox transformations of N that lead to N 2 O production (nitrification and hypoxic denitrification) and N 2 O consumption (suboxic denitrification), and is presented here for the first time. We perturb both submodels by modifying the key parameters of the N 2 O cycling pathways (nitrification rates; NH + 4 uptake; N 2 O yields under oxic, hypoxic and suboxic conditions) and determine a set of optimal model parameters by minimisation of a cost function against four databases of N cycle observations. Our estimate of the global oceanic N 2 O flux resulting from this cost function minimisation derived from observed and model pN 2 O concentrations is 2.4 ± 0.8 and 2.5 ± 0.8 Tg N yr −1 for the two N 2 O submodels. These estimates suggest that the currently available observational data of surface pN 2 O constrain the global N 2 O flux to a narrower range relative to the large range of results presented in the latest IPCC report.

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Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer

Cited by 34 publications

References 71 publications

Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

New insights on the role of organic speciation in the biogeochemical cycle of dissolved cobalt in the southeastern Atlantic and the Southern Ocean

Constraints on global oceanic emissions of N<sub>2</sub>O from observations and models

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Nitrogen uptake by phytoplankton in the Atlantic sector of the Southern Ocean during late austral summer

Cited by 34 publications

References 71 publications

Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year

New insights on the role of organic speciation in the biogeochemical cycle of dissolved cobalt in the southeastern Atlantic and the Southern Ocean

Constraints on global oceanic emissions of N&lt;sub&gt;2&lt;/sub&gt;O from observations and models

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About

Constraints on global oceanic emissions of N<sub>2</sub>O from observations and models