Realization of new production in coastal upwelling areas: A means to compare relative performance

A theoretical basis for analyzing new production of upwelling centers under various conditions and for comparing the relative performance of different upwelling centers has been developed using the concept of shift-up or acceleration of N03uptake. NO,concentration at the beginning of an upwelling cycle determines the rate of acceleration, the maximal specific NO,uptake rate, and the maximal new production rate achieved. The relationship between initial NO,concentration and new production rate is nonlinear and a doubling of initial NO,concentration results in a threefold increase in new production. The tendency for new biomass to increase during an upwelling cycle varies widely between different upwelling regions and, by comparing theoretical predictions with data, the performance of an upwelling system can be judged against optimal expectations and the realization of potential new production by the system estimated. Among upwelling centers at Cap Blanc (northwest Africa), 15% (off the coast of Peru), and Point Conception (California), the least of this potential is realized at Point Conception. New production, that portion of the primary production based upon entry of new primary nutrient into the euphotic zone, is the basis for net transfer of CO2 from the atmosphere to the ocean and of the transport of C to the deep ocean by sinking of particles (Eppley and Peterson 1979; Martin et al. 1987). One definition of new production is the productivity that results from the upward vertical flux of N03(Dugdale and Goering 1967) and consequently the uptake of that N03by phytoplankton. This flux proceeds relatively slowly over most of the oceans, more actively along the equatorial divergences, and very rapidly in coastal upwelling regions. It follows that the coastal upwelling regions also must contribute a disproportionately large share of global new production (Ryther 1969). Examination and modeling of the entire productivity cycle occurring in a coastal upwelling system yields information necessary 1 Present address: Department of Biological Sciences, University of Southern California, Los Angeles 90089. Acknowledgments This study was supported by the French Centre National de la Recherche Scientifique (UA 353), National Science Foundation grant OCE8710774, and NASA grant 161-30-33-40-55 to C. 0. Davis. We thank all those at CNRS and the Laboratoire de Physique et Chimie Marines for making this study possible. to understand the capacity for new production in the area. The changes in biological and nutrient processes with time as water drifts away from an upwelling center have been described by MacIsaac et al. (1985), Dugdale and Wilkerson (198 5), and Wilkerson and Dugdale (1987). In a conveyor-belt type of scheme, upwelled phytoplankton adapt to high light and high nutrients at the surface, but at first there is little nutrient uptake due to small population size and low specific uptake rates. Farther downstream there are increases in N03uptake rates and population size, and eventually high uptake rates result in sudden nutrient depletion. Sinking out of phytoplankton (that can no longer take up nutrients) occurs at various points along the conveyor belt, although most sinking probably occurs when nutrients become fully depleted. This concept arose primarily from investigations at 15”S, off Peru, where an upwelling plume has been known to occur at the same location over most of the year (Gunther 1936; Zuta and Urquino 1972) and from studies at Point Conception, California (Wilkerson and Dugdale 1987; Dugdale and Wilkerson 1989), and is applicable to the upwelling center at Cape Town, South Africa, that develops a similar plume (Andrews and Hutchings 1980). It does not have rigid constraints and can be applied to regions where the location of maximal upwelling intensity