1Laboratoire d'Océanologie et des Géosciences, UMR8187, INSU-CNRS – Université Lille Nord de France, ULCO, 62930 Wimereux, France
2Hellenic Centre for Marine Research, Institute of Oceanography, 71003 Heraklion, Crete, Greece
3LMGEM, Laboratoire de Microbiologie, Géochimie et Ecologie Marines, UMR6117, INSU-CNRS – Université de la Méditerranée, Centre d'Océanologie de Marseille, Campus de Luminy Case 901, 13288 Marseille cedex 9, France
4Observatoire Océanologique de Banyuls, UMS2348, INSU-CNRS, 66650 Banyuls/mer, France
5Université Pierre et Marie Curie-Paris VI, UMS2348, Observatoire Océanologique de Banyuls, 66650 Banyuls/mer, France
6Laboratoire d'Océanographie Microbienne, UMR7621, INSU-CNRS – Observatoire Océanologique, 66650 Banyuls/mer, France
7Université Pierre et Marie Curie-Paris VI, UMR7621, Laboratoire d'Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
8LOPB, Laboratoire d'Océanographie Physique et Biogéochimique, UMR6535, INSU-CNRS – Université de la Méditerranée, Centre d'Océanologie de Marseille, Campus de Luminy Case 901, 13288 Marseille cedex 9, France
*present address: Laboratoire d'Océanographie de Villefranche, UMR7093, INSU-CNRS, 06230 Villefranche-sur-Mer, France
**present address: Université Pierre et Marie Curie-Paris VI, Laboratoire d'Océanographie de Villefranche, UMR7093, 06230 Villefranche-sur-Mer, France
Received: 12 Nov 2010 – Discussion started: 09 Dec 2010
Abstract. We examined the effects of nutrient additions on rates of 14C-based particulate and dissolved primary production as well as O2-based metabolic rates in surface waters (8 m) of three anticyclonic eddies, located in the Western, Central and Eastern Mediterranean. Ship-board microcosm experiments employing additions of inorganic nitrogen (+N) and phosphorus (+P), alone and in combination (+NP), were conducted in June/July 2008 during the BOUM (Biogeochemistry from the Oligotrophic to the Ultra-oligotrophic Mediterranean) cruise. In all three experiments, particulate primary production was significantly stimulated by the additions of nitrogen (+N, +NP) while no effect was observed with the addition of phosphorus alone (+P). Percent extracellular release of photosynthate (PER) displayed the lowest values (4–8 %) in the +NP treatment. Among the three treatments (+N, +P, +NP), the +NP had the strongest effect on oxygen metabolic rates, leading to positive values of net community production (NCP > 0). These changes of NCP were mainly due to enhanced gross primary production (GPP) rather than reduced dark community respiration rates (DCR). In all three sites, in +NP treatment autotrophic production (whether expressed as GPP or PPtotal) was sufficient to fulfil the estimated carbon requirements of heterotrophic prokaryotes, while addition of nitrogen alone (+N) had a weaker effect on GPP, resulting in metabolically balanced systems. At the three sites, in treatments with N (+N, +NP), phytoplankton and heterotrophic prokaryote production were positively correlated. Heterotrophic conditions were observed in the Control and +P treatment at the central and eastern sites, and autotrophic production was not sufficient to supply estimated bacterial carbon demand, evidence of a decoupling of phytoplankton production and consumption by heterotrophic prokaryotes.
Revised: 07 Jun 2011 – Accepted: 06 Sep 2011 – Published: 14 Sep 2011
Lagaria, A., Psarra, S., Lefèvre, D., Van Wambeke, F., Courties, C., Pujo-Pay, M., Oriol, L., Tanaka, T., and Christaki, U.: The effects of nutrient additions on particulate and dissolved primary production and metabolic state in surface waters of three Mediterranean eddies, Biogeosciences, 8, 2595-2607, doi:10.5194/bg-8-2595-2011, 2011.