The occurrence of faecal material in relation to different pelagic systems in the Southern Ocean and its importance for vertical flux

Abstract:During the SO-JGOFS-Polarstern-cruise in Oct/Nov 1992, faecal pellet abundance and distribution were determined in order to assess the impact of zooplankton grazing and defecation within the following three typical Antarctic plankton regimes in the Atlantic sector: the Marginal Ice Zone (MIZ), the southern Antarctic Circumpolar Current (ACC) and the Polar Frontal region (PFr). In contrast to the more southern regions, the PFr was characterised by the occurrence of relatively dense phyto-plankton blooms and high copepod concentrations. Faecal pellets were relatively abundant in the MIZ reaching up to > 105 µg faecal pellet carbon (FPC) m-3, whereas the values in the more northern regions were about one to two orders of magnitude lower: about 6 µg FPC m-3 in the southern ACC and less than 1 µm FPC m-3 in the PFr. Thus, the region with the highest phyto- and zooplankton concentrations showed by far the lowest faecal pellet standing stock concentrations. These results were compared to other regions in the Southern Ocean and to other regions in the world oceans and possible reasons for this situation and the potential ecological impact are discussed. Our investigations show, that not only the biomass of phytoplankton and zooplankton, but also mainly the structures of the plankton communities are decisive for sedimentation potentials of carbon and silica via faecal pellets in the different regions of the ocean.