Koeve, W.

Zentrum für marine Umweltwissenschaften (Marum), Universität Bremen, Postfach 330440, D-28334 Bremen, Germany, E-mail: w.koeve@web.de

The carbon to nitrogen ratio of net community production in the North Atlantic Ocean - a synthesis

The concept of the constancy of the relative proportions of major elements of biogenic organic matter (C, N, P, O₂) and the related processes of production and decay (e.g. new production, remineralisation in the deep ocean) has been paradigmatic to marine biogeochemistry prior to JGOFS. During the JGOFS decade evidence has accumulated that the carbon to nitrogen ratio of net community production (NCP-C:N) can deviate significantly from the accepted C:N ratio of particulate organic matter and that of deep ocean remineralisation (6.6 to 7.3). Values as high as 14 to 15 have been suggested both for the spring phytoplankton bloom observed during NABE as well as for spring-summer integrals in the mesotrophic North Atlantic. In this presentation the current knowledge and open questions concerning the NCP-C:N in the North Atlantic are summarised. It is shown that (a) earlier estimates of NCP-C:N during spring blooms (NABE) are overestimates due to incomplete treatment of pre-formed values on NCP estimates, (b) spring-summer integrals of NCP-C:N range from about 10 to 11. The available evidence suggests that in the North Atlantic little carbon overconsumption is associated with the diatom spring bloom. Excess carbon production appears to be associated with summer time NCP. The relative role of seasonal storage in low-N DOM (dissolved organic matter) and N₂-fixation for NCP-C:N are discussed.