JOURNAL OF PLANKTON RESEARCH | VOLUME 16 | NUMBER 8 | PAGES 1059-1069 | 1994
© Oxford University Press
research-article |
A Lagrangian model of phytoplankton photosynthetic response in the upper mixed layer
1Department of Marine Science and Technology, Tokyo University of Fisheries 4-5-7 Konan, Minato-ku, Tokyo 108, Japan Department of Marine Earth & Atmospheric Sciences Box 8208, North Carolina State University, Raleigh, NC 27695, USA
Received on July 30, 1993; accepted on March 29, 1994 A previously developed Lagrangian model considered the distribution and light exposure of individual phytoplankton cells in a weakly stratified upper ocean layer mixed by depth-dependent turbulence. This model is coupled with a phytoplankton photoresponse model, previously applied in a Eulerian context, that includes a temporally decaying dependence on inhibitory light exposure. The combined model output provides the trajectory, light experience and photoresponse of each individual, or the photoresponse central tendency and variability of the population that occurs at a given depth at a given time. The time dependence of the photoresponse is the main variable considered and determines the shape of the vertical profile of primary production. Shorter response times yield a strong photoinhibition event that is nearly synchronous with inhibiting incident radiation. Longer response times are characterized by weaker photoinhibition events that outlive the occurrence of the inhibiting incident radiation for an interval related to the imposed time constant. Under the depth-dependent turbulent mixing regime imposed, photoinhibition is detectable even at wind speeds up to 10 m s–1. Modeling and technological approaches that compare the bulk characteristics of populations to the statistical characteristics of the individuals forming those populations are both under active development. A fruitful feedback relationship is likely in the near future.