THEORETICAL LIMITS OF OXYGEN-CARBON AND OXYGEN-NITROGEN RATIOS DURINGPHOTOSYNTHESIS AND MINERALIZATION OF ORGANIC-MATTER IN THE SEA

It is frequent to observe disagreements between the relationships R-C = -Delta O-2/Delta C and R-N = -Delta O-2/Delta N found during photosy nthesis-mineralisation studies in the ocean and those expected accordi ng to the Redfield plankton composition. That is because R-C and R-N d epend on the C/N and Carbohydrates/Lipids (Cbh/Lip) ratios of the orga nic matter. Starting from the mean biochemical composition of the main groups of phytoplankton biomolecules and from the stoichiometry of ph otosynthesis-mineralisation, we establish a new formulation to enable us to calculate R-C and R-N as a function of C/N and Cbh/Lip ratios in dependent of the variance in the N/P ratio. The approach proposed here permits the theoretical limits of R-C and R-N to be calculated. The R -C value can vary between 1 and 1.58 while R-N can vary between 5.8 an d infinity with the interrelationships between the ratios being define d by R-N/R-C=C/N which, in its turn, can vary between 3.67 and infinit y. For a given R-C the limits of R-N become narrower and vice versa. W hen C/N ratio is fixed the limits of the R-C and R-N values also becom e narrower. A graphic representation to check and visualise these limi ts and other experimental biochemical composition values is developed. According to the average value of the Cbh/Lip relationship, 0.82 in c arbon, recovered from the literature and for a C/N = 106/16, the estim ate mean R-C and R-N values are 1.41 and 9.33 respectively which are c oincident with previous ratios given by other authors.