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    Optimality-based model of phytoplankton growth and diazotrophy (2013)
    Inter Research
    In:  Marine Ecology Progress Series, 489 . pp. 1-16.
    Details
    Publication Date: 2019-09-24
    Description: The notion that excess phosphorus (P) and high irradiance favour pelagic diazotrophy is difficult to reconcile with diazotroph behaviour in laboratory experiments and also with the observed distribution of N2-fixing Trichodesmium, e.g. in the relatively nitrogen (N)-rich North Atlantic Ocean. Nevertheless, this view currently provides the state-of-the-art framework to understand both past dynamics and future evolution of the oceanic fixed N inventory. In an attempt to provide a consistent theoretical underpinning for marine autotrophic N2 fixation we derive controls of diazotrophy from an optimality-based model that accounts for phytoplankton growth and N2 fixation. Our approach differs from existing work in that conditions favourable for diazotrophy are not prescribed but emerge, indirectly, from trade-offs among energy and cellular resource requirements for the acquisition of P, N, and carbon. Our model reproduces laboratory data for a range of ordinary phytoplankton species and Trichodesmium. The model predicts that (1) the optimal strategy for facultative diazotrophy is switching between N2 fixation and using dissolved inorganic nitrogen (DIN) at a threshold DIN concentration; (2) oligotrophy, especially in P and under high light, favours diazotrophy; (3) diazotrophy is compatible with DIN:DIP supply ratios well above Redfield proportions; and (4) communities of diazotrophs competing with ordinary phytoplankton decouple emerging ambient and supply DIN:DIP ratios. Our model predictions appear in line with major observed patterns of diazotrophy in the ocean. The predicted importance of oligotrophy in P extends the present view of N2 fixation beyond a simple control by excess P in the surface ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.3354/meps10449
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Internal-wave induced and double-diffusive nutrient fluxes to the nutrient-consuming surface layer in the oligotrophic subtropical North Atlantic (2004)
    Springer
    In:  Ocean Dynamics, 54 . pp. 1-7.
    Details
    Publication Date: 2017-02-06
    Description: In the literature, an inconsistency exists between estimates of biotically-effected carbon export inferred from large-scale geochemical studies (Jenkins 1982; 47 gC m−2 a−1) and local measurements of turbulent nutrient supply (Lewis et al. 1986; 4 gC m−2 a−1) in the eastern subtropical North Atlantic. Nutrient supply to the upper ocean by turbulent mixing is reexamined using local standard oceanographic measurements and high-resolution vertical profiles of nutrients averaged over a large region directly comparable to that investigated by Jenkins (1982).
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s10236-003-0060-9
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Modeling abiotic production of apparent oxygen utilisation in the oligotrophic subtropical North Atlantic (2005)
    Springer
    In:  Ocean Dynamics, 55 (1). pp. 28-33.
    Details
    Publication Date: 2017-02-06
    Description: Apparent oxygen utilisation is potentially biased by abiotic, physical processes. Using a coupled 3-D circulation-oxygen model, this potential is quantitatively estimated for a region in the eastern subtropical North Atlantic, called the Beta Triangle, where an inconsistency exists between observational estimates of high carbon export from the euphotic zone, based on oxygen utilisation rates in the thermocline (Jenkins 1982), and those of low nutrient supply to the euphotic zone (Lewis et al. 1986, 2004). Our results indicate that in the upper ocean, the Jenkins (1982) estimate is indeed biased high by approximately 10% due to abiotic processes feigning respiration, thus contributing to the apparent inconsistency. Vertical integration, however, yields an abiotic fraction of less than 3%, so the apparent observational discrepancy can not be resolved.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s10236-005-0109-z
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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