A physical-biochemical model of plankton productivity and nitrogen cyclingin the Black Sea

A one-dimensional, vertically resolved, physical-biochemical upper ocean mo del is utilized to study plankton productivity and nitrogen cycling in the central Black Sea region characterized by cyclonic gyral circulation. The m odel is an extension of the one given by Oguz et al. (1996, J, Geophys. Res . 101, 16585-16599) with identical physical characteristics but incorporati ng a multi-component plankton structure in its biological module, Phytoplan kton are represented by two groups, typifying diatoms and flagellates, Zoop lankton are also separated into two groups: microzooplankton (nominally <20 0 mu m) and mesozooplankton (0.2-2 mm), The other components of the biochem ical model are detritus and nitrogen in the forms of nitrate and ammonium. The model incorporates, in addition to plankton productivity and organic ma tter generation, nitrogen remineralization (ammonification) and ammonium ox idation (nitrification) in the water column. Numerical simulations ape desc ribed and compared with the available data from the central Black Sea. The main seasonal and vertical characteristics of phytoplankton and nutrient dy namics inferred from observations appear to be reasonably well represented by the model. Fractionation of the biotic community structure is shown to l ead to increased plankton productivity during the summer period following t he diatom-based early spring (March) bloom. The annual nitrogen budget for the euphotic zone reveals the substantial role of recycled nitrogen in the surface waters of the Black Sea. (C) 1999 Elsevier Science Ltd. All rights reserved.