Recent interest in the importance of the global carbon cycle, especially with respect to łglobal warming,˛ has resulted in renewed interest in a the study of new primary production. Historically, it has been recognized that as much as 50% of the production in the world's oceans occurs in eastern boundary current locales such as Monterey Bay, where this research was conducted. The fundamental goal of this research has been to evaluate two problems: first, whether the paradigm łnitrate uptake equals new production˛ still holds, and second, to determine whether it is desirable or even possible to separate the interrelated phenomena of primary and new production.

The shift-up model, expanded to include other substrates and interactions including silicate, carbon and light, provides a robust description of the associated rates and processes during upwelling. Rates of NO3, NH4 and urea uptake were measured, representing the first comprehensive annual study of phytoplankton nitrogenous utilization in a coastal upwelling regime. NO3 dominated throughout the year. Total N uptake demonstrated simultaneous uptake and the absence of obvious preference or competition for NO3 and NH4. Urea provided <10% of the total nitrogen (N) uptake, but became significant with low total N uptake rates. Strong seasonal patterns of nitrogen utilization, with maximal uptake rates and biomass accumulation occuring during active upwelling was followed by more oligotrophic conditions during non-upwelling periods.

Grow-out experiments demonstrated that NO3 is the most limiting factor controlling new production and biomass accumulation; silicate was a controlling, but not limiting, factor. Shift-up was readily induced, closely regulated by the NO3 concentration, and not a function of chlorophyll-A concentration or detritus; similarly, carbon:nitrogen (C:N) composition and utilization ratios demonstrated nitrogen limitation.

Coupling of C and N uptake rates and metabolism was observed in an upwelling plume, with both regulated by ambient light. C and N utilization were not balanced over the short time scales associated with upwelling. The observations agreed with the predictions of the shift-up model, with initially high levels of C utilization, increasing NO3 utilization (and decreased C uptake), and finally a return to high C utilization with a shift towards NH4 as a nitrogenous source. Diurnal patterns of C and N uptake were variable, emphasizing the need for caution in interpreting short-term incubations, or in assuming steady-state kinetics between C and N utilization.

A predictive model of new production which utilizes AVHRR imagery and the physiological (shift-up) results demonstrates that first principles of phytoplankton physiology may be used to determine new production. This model also provides insight into the underlying physiological responses associated with upwelling, and represents the first modeling effort to do so in depth.