Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Thomalla, Sandy J.; Waldron, H. N.; Lucas, Michael I.; Read, J.F.; Ansorge, I. J.; Pakhomov, Evgeny A.

doi:10.5194/os-7-113-2011

Cited by 29 publications

(15 citation statements)

References 80 publications

(75 reference statements)

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“…4). This is consistent with previous results of low f -ratios in the Indian (f = 0.07 ± 0.03) (Thomalla et al, 2011) and Pacific basins (Sambrotto and Mace, 2000) (Table 2). These results imply that this region of the Southern Ocean is dominated by urea re-cycling within the microbial loop, with little carbon export, little atmospheric CO 2 "draw-down", and conservation of nitrogen in surface waters (LeFevre et al, 1998;Smetacek et al, 2004).…”

Section: The Subtropical Zonesupporting

confidence: 94%

“…Mesoscale eddies such as these provide important areas for local but significant POC export and biological CO 2 draw-down in an overall HNLC Southern Ocean. ∫ρN rates in the SAZ of the Atlantic measured in this study (10.3 mmol m −2 d −1 ) were slightly higher than those measured in the Australian sector in late spring/early summer (4.4±0.3 mmol m −2 d −1 ) (Savoye et al, 2004) and were comparable to the Indian sector in late summer (12.7 ± 7.9 mmol m −2 d −1 ) observations (Thomalla et al, 2011) (Table 3).…”

Section: The Subantarctic Zonesupporting

confidence: 55%

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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: The Subtropical Zonesupporting

confidence: 94%

Section: The Subantarctic Zonesupporting

confidence: 55%

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

et al. 2011

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“…1). The summer cruise was conducted on board the MV SA Agulhas from the 15 February to 11 March 2013 (Thomalla et al, 2013). Nitrogen uptake rates were estimated at two stations along the GoodHope line and two process stations (A and B) within the subantarctic zone.…”

Section: Sampling and Analytical Methodsmentioning

confidence: 99%

A geographical and seasonal comparison of nitrogen uptake by phytoplankton in the Southern Ocean

2015

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The impact of light and nutrients (such as silicate and iron) availability on nitrogen uptake and primary production vary seasonally and regionally in the Southern Ocean. The seasonal cycle of nitrogen uptake by phytoplankton in the Southern Ocean is not fully resolved over an annual scale due to the lack of winter in situ measurements. In this study, nitrate and ammonium uptake rates were measured using 15 N tracers during a winter cruise in July 2012 and a summer cruise in February-March 2013. The winter cruise consisted of two legs: leg 1 extended from Cape Town to the ice margin along the GoodHope line and leg 2 stretched from the ice margin to Marion Island. The summer cruise was mostly focused on the subantarctic zone of the Atlantic sector. In winter, nitrogen uptake rates were measured at 55 and 1 % of the surface photosynthetically active radiation (sPAR). The summer uptake rates were measured at four light depths corresponding to 55, 30, 10 and 3 % sPAR. The integrated nitrate uptake rates during the winter cruise ranged from 0.17 to 5.20 mmol N m −2 d −1 (average 1.14 mmol N m −2 d −1 ) while the ammonium uptake rates ranged from 0.60 to 32.86 mmol N m −2 d −1 (average 6.73 mmol N m −2 d −1 ). During the summer cruise, the mean-integrated nitrate uptake rate was 0.20 mmol N m −2 d −1 with a range between 0.10 and 0.38 mmol N m −2 d −1 . The integrated ammonium uptake rate averaged 4.39 mmol N m −2 d −1 and ranged from 1.12 to 9.05 mmol N m −2 d −1 .The factors controlling nitrogen uptake in winter and summer were investigated. During the winter cruise, it was found that the different nitrogen uptake regimes were not separated by the fronts of the Antarctic Circumpolar Current (ACC). Light (in terms of day length) and ammonium concentration had the most influence on the nitrogen uptake. In the summer, increases in the mixed layer depth (MLD) resulted in increased nitrogen uptake rates. This suggests that the increases in the MLD could be alleviating nutrient limitations experienced by the phytoplankton at the end of summer.

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“…Anthropogenic climate change appears to be pushing the Antarctic Circumpolar Current poleward (Fyfe & Saenko, ; Gille, ; Biastoch et al ., ) due to warming and fresh water inputs (Böning et al ., ). The Southern Ocean covers ~ 10% of the earth's surface area (Aronson et al ., ), and due to the important role it plays in sequestering anthropogenic CO 2 (Sabine et al ., ; Mikaloff Fletcher et al ., ) through both physiochemical processes and the ‘biological pump’ of CO 2 fixation and export from the euphotic zone to the ocean depths (Thomalla et al ., ), the changes taking place in Antarctic waters could have major global ecological consequences (Liu & Curry, ). This is emphasized by the fact that changes to ecosystems in the south polar region (e.g.…”

Section: The Southern Oceanmentioning

confidence: 99%

Key microbial drivers in Antarctic aquatic environments

et al. 2013

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Antarctica is arguably the world's most important continent for influencing the Earth's climate and ocean ecosystem function. The unique physico-chemical properties of the Southern Ocean enable high levels of microbial primary production to occur. This not only forms the base of a significant fraction of the global oceanic food web, but leads to the sequestration of anthropogenic CO2 and its transport to marine sediments, thereby removing it from the atmosphere; the Southern Ocean accounts for ~ 30% of global ocean uptake of CO2 despite representing ~ 10% of the total surface area of the global ocean. The Antarctic continent itself harbors some liquid water, including a remarkably diverse range of surface and subglacial lakes. Being one of the remaining natural frontiers, Antarctica delivers the paradox of needing to be protected from disturbance while requiring scientific endeavor to discover what is indigenous and learn how best to protect it. Moreover, like many natural environments on Earth, in Antarctica, microorganisms dominate the genetic pool and biomass of the colonizable niches and play the key roles in maintaining proper ecosystem function. This review puts into perspective insight that has been and can be gained about Antarctica's aquatic microbiota using molecular biology, and in particular, metagenomic approaches.

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Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Cited by 29 publications

References 80 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

A geographical and seasonal comparison of nitrogen uptake by phytoplankton in the Southern Ocean

Key microbial drivers in Antarctic aquatic environments

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