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  • 2005-2009  (7)
  • 1
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    Global warming may decrease nitrogen fixation by Trichodesmium (2005)
    In:  [Talk] In: ASLO Summer Meeting, 19.-24.6.2005, Santiago de Compostela, Spain .
    Details
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 2
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    Water column biology (2006)
    Details
    Publication Date: 2023-09-19
    Type: Report , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Report - other report
  • 3
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    Nitrogen and phosphorus co-limitation of bacterial productivity and growth in the Oligotrophic Sub-Tropical North Atlantic (2008)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 53 . pp. 824-834.
    Details
    Publication Date: 2018-08-14
    Description: Bacterial productivity and biomass are thought to be limited by dissolved organic carbon (DOC) in much of the world’s oceans. However, the mixed layer of oligotrophic oceans is often depleted in dissolved inorganic nitrogen and phosphate, raising the possibility that macronutrients may also limit heterotrophic bacterial growth. We used nutrient bioassay experiments to determine whether inorganic nutrients (N, P, Fe) and/or DOC could limit bacterial productivity and biomass in the central North Atlantic during the spring of 2004 (Mar–Apr). We observed that both heterotrophic bacterial productivity and biomass were co-limited by N and P in the oligotrophic North Atlantic, and additions of labile DOC (glucose) provided no stimulation unless N and P were also added. Flow cytometry results indicated that only a small subset of large cells high in nucleic acid content were responsible for the increased productivity in the combined NP amendments. In contrast, nutrient additions elicited no net change on the dominant component of the bacterial population, composed of small cells with relatively low nucleic acid content. In the combined NP treatments the relative increase in bacterial production was greater than that measured when phytoplankton productivity was relieved of nitrogen limitation. These results suggest that N and P co-limitation in the bacterial community results in increased competition between the heterotrophic and autotrophic components of the surface communities in the Central North Atlantic Ocean, and potentially impacts the cycling of organic matter by the bacterioplankton.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2008.53.2.0824
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Nutrient limitation of picophytoplankton photosynthesis and growth in the tropical North Atlantic (2008)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 53 . pp. 1722-1733.
    Details
    Publication Date: 2017-05-02
    Description: Identification of the proximal nutrient limiting primary production is a necessary first step toward evaluating the physiological state of phytoplankton communities and the biogeochemical constraints on the current oceanic carbon cycle. We conducted 48-h nutrient addition bioassay experiments to evaluate nitrogen, phosphorus, and iron limitation of primary productivity, net chlorophyll synthesis, and net increase in cell numbers of the dominant picophytoplankton from the tropical North Atlantic. Our results indicate that N was the proximal limiting factor for primary production during the autumn of 2002, followed by P and then Fe. Net chlorophyll synthesis was significantly stimulated by addition of N alone and further stimulated by addition of P. Analysis of picophytoplankton populations by analytical flow cytometry revealed a more complex response. Cellular red fluorescence, an index of cell chlorophyll content, increased in Prochlorococcus, Synechococcus, and picoeukaryotes in response to addition of NH4NO3 but was not affected by single or combined additions of P and Fe. In contrast, cell abundance in these picophytoplankton populations increased only after combined N and P (63% of comparisons) or N and Fe (21% of comparisons) additions. Thus, our experiments revealed that chlorophyll synthesis and primary production were limited by the availability of nitrogen alone, while net increase in cell abundance was colimited by N and P or N and Fe in the majority of these picophytoplankton populations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2008.53.5.1722
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Large-scale distribution of Atlantic nitrogen fixation controlled by iron availability (2009)
    Nature Publishing Group
    In:  Nature Geoscience, 2 . pp. 867-871.
    Details
    Publication Date: 2017-02-22
    Description: Oceanic fixed-nitrogen concentrations are controlled by the balance between nitrogen fixation and denitrification. A number of factors, including iron limitation, can restrict nitrogen fixation, introducing the potential for decoupling of nitrogen inputs and losses. Such decoupling could significantly affect the oceanic fixed-nitrogen inventory and consequently the biological component of ocean carbon storage and hence air–sea partitioning of carbon dioxide. However, the extent to which nutrients limit nitrogen fixation in the global ocean is uncertain. Here, we examined rates of nitrogen fixation and nutrient concentrations in the surface waters of the Atlantic Ocean along a north–south 10,000 km transect during October and November 2005. We show that rates of nitrogen fixation were markedly higher in the North Atlantic compared with the South Atlantic Ocean. Across the two basins, nitrogen fixation was positively correlated with dissolved iron and negatively correlated with dissolved phosphorus concentrations. We conclude that inter-basin differences in nitrogen fixation are controlled by iron supply rather than phosphorus availability. Analysis of the nutrient content of deep waters suggests that the fixed nitrogen enters North Atlantic Deep Water. Our study thus supports the suggestion that iron significantly influences nitrogen fixation5, and that subsequent interactions with ocean circulation patterns contribute to the decoupling of nitrogen fixation and loss.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/NGEO667
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Iron limits primary productivity during spring bloom development in the central North Atlantic (2006)
    Wiley
    In:  Global Change Biology, 12 (4). pp. 623-624.
    Details
    Publication Date: 2018-05-16
    Description: We present in situ biophysical measurements and bioassay experiments that demonstrate iron limitation of primary productivity during the spring bloom in the central North Atlantic. Mass balance calculations indicate that nitrate drawdown is iron (Fe)-limited and that aeolian Fe supply to this region cannot support maximal phytoplankton growth during the bloom. Using a simple simulation model, we show that relief of Fe limitation during the spring bloom can increase nitrate drawdown and, hence, new primary production, by 70%. We conclude that the episodic nature of iron supplied by dust deposition is an important factor controlling the dynamics of the spring bloom. From this, we hypothesize that variability in the timing and magnitude of the spring bloom in response to aeolian Fe supply will affect carbon drawdown and food web dynamics in the central North Atlantic
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1111/j.1365-2486.2006.01122.x
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Relative influence of nitrogen and phosphorous availability on phytoplankton physiology and productivity in the Oligotrophic Sub-Tropical North Atlantic Ocean (2008)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 53 (1). pp. 291-305.
    Details
    Publication Date: 2018-08-14
    Description: Nutrient addition bioassay experiments were performed in the low-nutrient, low-chlorophyll oligotrophic subtropical North Atlantic Ocean to investigate the influence of nitrogen (N), phosphorus (P), and/or iron (Fe) on phytoplankton physiology and the limitation of primary productivity or picophytoplankton biomass. Additions of N alone resulted in 1.5-2 fold increases in primary productivity and chlorophyll after 48 h, with larger (~threefold) increases observed for the addition of P in combination with N (NP). Measurements of cellular chlorophyll contents permitted evaluation of the physiological response of the photosynthetic apparatus to N and P additions in three picophytoplankton groups. In both Prochlorococcus and the picoeukaryotes, cellular chlorophyll increased by similar amounts in N and NP treatments relative to all other treatments, suggesting that pigment synthesis was N limited. In contrast, the increase of cellular chlorophyll was greater in NP than in N treatments in Synechococcus, suggestive of NP co-limitation. Relative increases in cellular nucleic acid were also only observed in Synechococcus for NP treatments, indicating co-limitation of net nucleic acid synthesis. A lack of response to relief of nutrient stress for the efficiency of photosystem II photochemistry, Fv :Fm, suggests that the low nutrient supply to this region resulted in a condition of balanced nutrient limited growth, rather than starvation. N thus appears to be the proximal (i.e. direct physiological) limiting nutrient in the oligotrophic sub-tropical North Atlantic. In addition, some major picophytoplankton groups, as well as overall autotrophic community biomass, appears to be co-limited by N and P.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lo.2008.53.1.0291
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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