Marine Biology

, Volume 39, Issue 2, pp 111–120 | Cite as

Nitrogen assimilation by phytoplankton and other microorganisms in the surface waters of the central North Pacific Ocean

  • R. W. Eppley
  • J. H. Sharp
  • E. H. Renger
  • M. J. Perry
  • W. G. Harrison


Assimilation rates of 15N-labelled ammonium, urea, and nitrate by plankton in the upper euphotic zone were measured in 2 summer, 2 winter, and 1 spring cruise in the central North Pacific Ocean. Average rates of ammonium plus urea assimilation could not be determined precisely, but were estimated to be 7 to 25 μg-at. N m-3 day-1. Indirect evidence suggested that non-photosynthetic microorganisms contributed to these rates. Nitrate assimilation was negligible in the upper waters considered in this report (above the chlorophyll maximum and the nutricline). Potential, nitrate-saturated rates were in the range 1 to 8 μg-at. N m-3 day-1. Seasonal comparison showed lowest rates of both carbon and nitrogen assimilation rates per chlorophyll a in winter.


Nitrate Chlorophyll Urea Phytoplankton Assimilation 
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Copyright information

© Springer-Verlag 1977

Authors and Affiliations

  • R. W. Eppley
    • 1
  • J. H. Sharp
    • 1
  • E. H. Renger
    • 1
  • M. J. Perry
    • 1
  • W. G. Harrison
    • 1
  1. 1.Institute of Marine ResourcesUniversity of CaliforniaLa JollaUSA

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