Seasonal variation of phytoplankton community structure and nitrogen uptake regime in the Indian Sector of the Southern Ocean

Mengesha, S; Dehairs, Frank; Fiala, Michel; Elskens, Marc; Goeyens, Léo

doi:10.1007/s003000050302

Cited by 67 publications

(29 citation statements)

References 28 publications

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“…New production estimates, on the other hand do not discriminate on a size basis and represents the potential export of both dissolved and particulate material. This is consistent with other observations in both the Indian (Mengesha et al, 1998) and Pacific sector (Savoye et al, 2004) of the Southern Ocean and highlights the important role of this ocean in the global carbon cycle.…”

Section: N Estimates and 234 Th Export Fluxsupporting

confidence: 93%

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

et al. 2011

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Abstract. As part of the Bonus-GoodHope (BGH) campaign, 15 N-labelled nitrate, ammonium and urea uptake measurements were made along the BGH transect from Cape Town to ∼60 • S in late austral summer, 2008. Our results are categorised according to distinct hydrographic regions defined by oceanic fronts and open ocean zones. High regenerated nitrate uptake rate in the oligotrophic Subtropical Zone (STZ) resulted in low f -ratios (f = 0.2) with nitrogen uptake being dominated by ρurea, which contributed up to 70 % of total nitrogen uptake. Size fractionated chlorophyll data showed that the greatest contribution (>50 %) of picophytoplankton (<2 µm) were found in the STZ, consistent with a community based on regenerated production. The Subantarctic Zone (SAZ) showed the greatest total integrated nitrogen uptake (10.3 mmol m −2 d −1 ), mainly due to enhanced nutrient supply within an anticyclonic eddy observed in this region. A decrease in the contribution of smaller size classes to the phytoplankton community was observed with increasing latitude, concurrent with a decrease in the contribution of regenerated production. Higher f -ratios observed in the SAZ (f = 0.49), Polar Frontal Zone (f = 0.41) and Antarctic Zone (f = 0.45) relative to the STZ (f = 0.24), indicate a higher contribution of NO − 3 -uptake relative to total nitrogen and potentially higher export production. High ambient regenerated nutrient concentrations are indicative of active regeneration processes throughout the transect and ascribed to late summer season sampling. Higher depth integratedCorrespondence to: W. R. Joubert (wjoubert@csir.co.za) uptake rates also correspond with higher surface iron concentrations. No clear correlation was observed between carbon export estimates derived from new production and 234 Th flux. In addition, export derived from 15 N estimates were 2-20 times greater than those based on 234 Th flux. Variability in the magnitude of export is likely due to intrinsically different methods, compounded by differences in integration time scales for the two proxies of carbon export.

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Section: N Estimates and 234 Th Export Fluxsupporting

confidence: 93%

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

et al. 2011

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“…Dortch 1990, Flynn et al 1997, Lomas & Glibert 1999a, Page et al 1999, with studies in the Southern Ocean also supporting this relationship (Glibert et al 1982, Owens et al 1991, Mengesha et al 1998. A recent model proposed the co-limitation of nitrate and phytoplankton growth in HNLC areas by iron, light and ammonium (Armstrong 1999).…”

Section: Specific Nutrient Depletionmentioning

confidence: 85%

“…Ammonium concentrations are generally low early in the spring and nitrogen uptake tends to be dominated by nitrate use, with consequently high ƒ ratios. However, despite the fact that nitrate concentrations are rarely depleted to what would be considered limiting concentrations in temperate oceanic areas, ammonium utilization becomes increasingly important during the course of the season, with a shift from predominantly new to regenerated production (Mengesha et al 1998). Increasing evidence suggests that the reduced forms of N, such as ammonium and urea, may be less temperature-dependent than nitrate, so further increasing their importance as N sources at low temperatures.…”

Section: Specific Nutrient Depletionmentioning

confidence: 99%

Regulation by low temperature of phytoplankton growth and nutrient uptake in the Southern Ocean

Reay¹,

Priddle²,

Nedwell³

et al. 2001

Mar. Ecol. Prog. Ser.

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During oceanographic cruises in 1996 and 1998, phytoplankton from 15 stations in the southwest Atlantic sector of the Southern Ocean were incubated at ambient temperature and 2 elevated temperatures (ambient plus 3°C, and ambient plus 6°C). Rates of growth, nutrient depletion, 15 N-nitrate uptake and nutrient interaction were all studied. Microalgal growth rate showed a strong positive relationship to temperature elevation, indicating ambient temperatures were sub-optimal for the phytoplanktonic community as a whole. Ratios of silicate uptake to chlorophyll a increase were high at ambient temperatures and showed a strong negative relationship with temperature elevation. Nitrate uptake rates, measured by 15 N-nitrate incorporation, showed a consistent trend of increased uptake rate at elevated temperature. Specific nitrate-depletion rates, 15 N-nitrate uptake rates, and the ƒ ratio all showed an inverse relationship to increasing ammonium concentration. The results of this study imply that ambient temperature, in addition to direct iron limitation, is important in the maintenance of the high nutrient, low chlorophyll conditions common to the Southern Ocean.

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“…The depth of the upper mixed layer (UML) was determined as the depth where a change of σ t > 0.05 occurred over a 5 m depth interval. Vertical water column stability (E) was calculated according to Mengesha et al (1998): E = dσ t /dz × 1/σ t(avg) where dσ t /dz is the density vertical gradient, dz is 50 m depth, and σ t(avg) is the average density.…”

Section: Methodsmentioning

confidence: 99%

Phytoplankton spatial distribution patterns along the western Antarctic Peninsula (Southern Ocean)

Garibotti¹,

Vernet²,

Ferrario³

et al. 2003

Mar. Ecol. Prog. Ser.

157

117

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This paper describes spatial distribution patterns of the phytoplankton community (composition, cell abundance and biomass concentration) in relation to local environmental conditions in the Southern Ocean. Sampling was performed during summer 1997 off the coast of the western Antarctic Peninsula between Anvers Island and Marguerite Bay. Phytoplankton was characterized by relatively low biomass throughout most of the study area and was dominated by nanoalgae (< 20 µm). Phytoplankton varied along an on-offshore gradient, with decreasing total cell abundance, chlorophyll a (chl a) concentration and carbon biomass toward the open ocean. Chl a concentration showed surface or subsurface maxima in coastal and middle-shelf waters, and deep maxima between ~40 and 100 m in oceanic waters. Across-shelf variability in phytoplankton correlated with vertical stability in the water column, which appears to be the major parameter affecting phytoplankton community structure in the area. We hypothesize that the deep chl a maximum offshore may be associated with iron limitation in near-surface waters and higher iron concentration in 'winter waters' (subsurface remnant of Antarctic Surface Waters). On a smaller spatial scale, a cluster analysis showed great regional variability in phytoplankton assemblages. The area was divided into 4 main regions based on differences in the phytoplankton composition and concentration. Three peaks in phytoplankton abundance were found on a north-to-south gradient in near-shore waters: a Cryptomonas spp. bloom near Anvers Island, a small unidentified phytoflagellate bloom in Grandidier Channel, and a diatom bloom in Marguerite Bay. These assemblages resemble different stages of the phytoplankton seasonal succession, and may be related to the progressive sea-ice retreat, which might have regulated the timing of the onset of the phytoplankton seasonal succession in a north-south gradient. Biological environmental factors, such as seeding of the water column by epontic algae and selective zooplankton herbivory, are hypothesized to affect community composition in coastal regions. We conclude that large-scale variability in phytoplankton community structure is related to water column physical conditions and possibly iron availability, while mesoscale variability, as seen in coastal waters, is more likely due to seasonal succession of different algae groups.

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Seasonal variation of phytoplankton community structure and nitrogen uptake regime in the Indian Sector of the Southern Ocean

Cited by 67 publications

References 28 publications

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

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

Regulation by low temperature of phytoplankton growth and nutrient uptake in the Southern Ocean

Phytoplankton spatial distribution patterns along the western Antarctic Peninsula (Southern Ocean)

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