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Nutrient fluxes to planktonic osmotrophs in the presence of fluid motion
Karp-Boss, L.; Boss, E.; Jumars, P.A. (1996). Nutrient fluxes to planktonic osmotrophs in the presence of fluid motion. Oceanogr. Mar. Biol. Ann. Rev. 34: 71-107
In: Oceanography and Marine Biology: An Annual Review. Aberdeen University Press/Allen & Unwin: London. ISSN 0078-3218, more
Peer reviewed article  

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    Nutrients (mineral); Plankton; Marine

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  • Karp-Boss, L.
  • Boss, E.
  • Jumars, P.A.

    We present solutions for nutrient transfer to osmotrophs in the full range of flow regimes for which solutions have been published, and we extend some of those solutions to new parameter domains and flow environments. These regimes include stagnant water; steady, uniform flow arising from swimming or sinking; steady shear flows; and fluctuating shear from dissipation of turbulence, as well as the combined effects of turbulence-induced shear and swimming or sinking. Solutions for nutrient fluxes cannot be carried over from one flow regime to another. In all cases, however, mass transfer increases with cell size and with flow velocity. Cell shape becomes particularly important at high flow velocities. For steady, uniform flow arising from sinking or swimming, we find asymptotic analytic and numerical solutions from the engineering literature superior to those in more common use within oceanography. These engineering solutions suggest flow effects an order of magnitude smaller than commonly supposed. A cell radius near 20µm is needed before swimming or sinking can be expected to increase the flux of nutrients, such as nitrate or phosphate, substantially (by more or equal to 50%) over the stagnant-water case. We find sound asymptotic solutions for the case of linear shear and supplement them with numerical solutions of our own to cover the range of cell sizes and shear rates of interest for phytoplankton. We extend them further to cover viscous shears from dissipating turbulence for cells smaller than the Kolmogorov scale (order of 1-6mm in the ocean). Our analysis suggests turbulence effects an order of magnitude greater than previously postulated, with a cell size of 60µm needed to experience substantial gain. Cell rotation, whether induced by the propulsion mechanism in swimming or passively by shear across the cell perimeter, will reduce the rate of nutrient transfer relative to a non-rotating cell unless the axis of rotation parallels the direction of flow. Although in calm water dinoflagellates by swimming are able to increase nutrient uptake, in strong turbulente they may not be able to maintain a rotational axis parallel to the direction of swimming or the direction of shear, resulting in a relative reduction in flux. Conversely, large chains of diatoms and filamentous cyanobacteria that span the radius of the smallest vortices are best able to take advantage of turbulence. Despite these deductions from a diversity of analytic and numerical solutions, unequivocal data to test the contribution of advection to nutrient acquisition by phytoplankton are scarce - owing, in large part, to the inability to visualize, record and thus mimic fluid motions in the vicinities of cells in natural flows.

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