Saggiomo¹, Vincenzo, Olga Mangoni², Monica Modigh¹, Carmela Ianni³, Paola Rivaro³ and GianCarlo Carrada²

¹Zoological Station “A. Dohrn”, Villa Comunale I, 80121 Naples, Italy, Tel: +39(081)5833240, Fax: +39(081)5833224, E-mail: saggiomo@szn.it, ²University of Naples “Federico II”, Naples, Italy and ³University of Genoa, Genoa, Italy

Primary production processes in the Ross Sea (Antarctica): limiting factors and system carrying capacity

The Ross Sea is one of the most productive areas of the Southern Ocean, with pronounced seasonal variations in phytoplankton biomass and production. Highest values of primary production are recorded trough austral spring till early summer. During summer primary production sharply decreases; micro-nutrient limitation and the deepening of the upper mixed layer have been invoked as major factors limiting phytoplankton growth. Primary production processes during summer in offshore and coastal waters both in ice free waters and in conditions of extensive ice coverage are presented. Spatial and temporal distributions of biomass (Chla), simulated in situ primary production, photosynthetic parameters (PvsE curves) and photosynthetic performance (Fv/Fm by means of a FRRF) are presented in relation to micro- and macro-nutrient concentrations. In conditions of extensive pack ice coverage, average Chla concentration was about three times the values recorded under ice-free conditions, but primary production was relatively lower. In contrast to a very high variability in phytoplankton biomass and production, photosynthetic parameters vary within narrow ranges. In situ primary production and photosynthetic parameters showed that, for most of the area, high primary production values occurred only within melting pack-ice and in the first five meters of the water column. Below this layer the photosynthetic capacity was notably depressed, despite similar conditions of water column stability, irradiance and phytoplankton biomass. This indicates a low carrying capacity of the pelagic ecosystem, due to iron limitation as shown by the low values of iron concentration and the Fv/Fm ratio.