Mayzaud, Patrick, Ahmed Errhif and Marc Boutoute

CNRS-INSU, Observatoire Océanologique, Laboratoire d'Océanographie de Villefranche, BP. 28, 06230 Villefranche sur mer, France, E-mail: mayzaud@obs-vlfr.fr

Carbon recycling by zooplankton in the Southern Ocean: Can we ignore it?

The current view on carbon recycling in the ocean has been entirely focussed on the processes associated either to bacteria, phytoplankton respiration or heterotrophic protozoan. Despite the occurrence of large populations of planktonic metazoan in the southern ocean and their variable distribution within the photic layer, zooplankton communities have received little attention in the context of CO₂ production. In the case of the Antarctic Ocean, a global view is possible to quantify this role in relation to community structure, regional and seasonal variability.

Using respiration rates obtained during the ANTARES cruises for the major zooplankton species at two seasons for the Indian sector of the Southern Ocean, values of oxygen consumption were transformed into CO₂ production. RQs used in such calculation were measured and the allometric relationship with size taken into consideration for realistic estimates. Regional budgets are established at the population levels using detailed population structure. The results indicated that, integrated values over the entire photic layer (0-200m), the CO₂ production of the copepod fraction of the population corresponded to a mean remineralization rate of about 30% of the local daily primary production both in spring and summer. When other groups such as euphausids, salps, ostracods, pteropods are considered this percentages increases dramatically mainly during the summer period. A comparison of the different regions of the Southern Ocean suggested that this contribution is more the rule than the exception and that it can hardly be ignored in the modelling of heterotrophic processes. Special attention is given to the special case of krill/salp interaction.