Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.

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Size-fractionated phytoplankton standing stocks and potential primary production (PPP) off the west and east coasts of South Island, New Zealand, were evaluated in austral winter and spring 1993. These are the first size-fractionated primary production data to be reported from the southern Subtropical Convergence (STC) and in oceanic New Zealand waters. Picophytoplankton (< 2 µm) formed > 30% of integrated chlorophyll a and daily PPP in most water types and seasons, except when the 20-200 µm size class dominated in west coast waters in spring and in the STC in winter and spring. In subtropical and STC waters, PPP was 30% higher than at similar latitudes in the North Atlantic Ocean. Interpretation of whether or not there was accumulation of chlorophyll a in the various water types and seasons depends on microzooplankton grazing, M96055 because mesozooplankton grazing and the proportion of chlorophyllous particulate matter sinking out of the upper water column was low. In the STC in spring, phytoplankton growth was slowing down (potential doubling times were at most 1.01 per day at 10 m and PPP per unit biomass was lower than in water masses to the north and south), probably because of decreasing concentrations of dissolved reactive silica. A sedimentation event of diatoms is postulated to have occurred in the STC soon after our spring sampling dates. The balance between algal growth and loss factors in the south-west Pacific depends on the unique combination of physical and chemical environmental conditions experienced there. The implications of the distribution of phytoplankton biomass and primary production by size-fraction for carbon export is discussed.

2012. Chattonella globosa is a member of Dictyochophyceae: reassignment to Vicicitus gen. nov., based on molecular phylogeny, pigment composition, morphology and life history.Chattonella globosa is a heterokont flagellate that has been previously assigned to the Class Raphidophyceae. Phylogenetic analyses of the nuclear encoded SSU, partial LSU, ITS1 rDNA and mitochondrial encoded COI clearly indicated that it is closely related to Dictyocha speculum and Dictyocha octonaria, Order Dictyochales, in the Class Dictyochophyceae. Moreover, High Performance Liquid Chromatography (HPLC) pigment analysis of Chattonella globosa revealed the presence of two acyl-oxyfucoxanthin derivatives, 199-butanoyl-oxyfucoxanthin and 199-hexanoyloxyfucoxanthin, pigments not found in members of the Raphidophyceae. In the late exponential growth phase a large number of smaller, less pigmented cells of Chattonella globosa, which acted like gametes, fused to give rise to a large multi-nucleate cell. At times two or more of these cells fused further to form a 'massive', plasmodium-like aggregate (up to 500 mm long). Chattonella globosa is also characterised by swift transformation of the globular, either small, uninucleate, or large, multi-nulceate motile cells, into amoeboid form. The multi-nucleate cell, plasmodium-like aggregate and amoeboid form are three major cell types shared by many dictyochophytes in their polymorphic life history but not raphidophytes. Based on the pigment composition, morphological and life history data we transfer Chattonella globosa to a new genus, Vicicitus gen. nov. of the Order Dictyochales, Class Dictyochophyceae, as Vicicitus globosus (Y. Hara et Chihara) F. H. Chang comb. nov.

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