Phytoplanktonic biomass synthesis: application to deviations from Redfield stoichiometry

Abstract

During biomass formation as a result of phytoplankton photosynthesis, CO₂ and the nutrients NO₃ and PO₄ are consumed and O₂ produced in fixed proportions known as the Redfield ratio. Broecker’s tracers, i.e., “NO” = O₂+R_N·NO₃, “PO” =O₂+R_P·PO₄, and “CO” = O₂+R_C·CO₂, remain constant during photosynthesis, because nutrients consumed are offset by O₂ formation. When one or several nutrients become depleted, the Redfield ratio no longer holds, and the tracers cease to remain constant. The main causes are formation of excess carbohydrates or lipids, N₂ fixation, or production of CaCO₃ plates by phytoplanktonic populations that have developed different strategies for obtaining the nutrients they need. This paper presents new tracers that remain constant, irrespective of whether or not Redfield stoichiometry is satisfied. Differences between the values of the new tracers and the values of the conventional tracers reveal the presence of anomalies in biomass production. They also allow quantification of any such anomalies, both globally and by depth stratum, and assessment of each individual anomaly separately, even when more than one anomaly occur simultaneously.