Southern-Atlantic phytoplankton community composition, distribution and response to relief of light and iron limitation

Abstract

Understanding the response of phytoplankton communities to specific environmental drivers in different Southern Ocean water masses is critical to improve projections under current threats of global change. We show the importance of understanding of the role the biological pump play in the future global climate and more specifically the effect of different phytoplankton communities. Different phytoplankton play different roles in the ocean biogeochemical cycles, especially carbon export, and thus on climate feedback processes. This study presents changes in the community composition across a South-Africa to Antarctic transect along with an assessment of the effects of increased micronutrients using a series of on-board iron/light bulk incubation experiments. Phytoplankton functional group compositions and distribution was assessed using their photosynthetic pigments. The smaller groups like Cyanobacteria and Chlorophytes were most abundant in the Sub-Tropical zone. Diatoms were dominant in the Sub-Antarctic, Polar Frontal, and - along with Phaeocystis antarctica - the Antarctic zone. This was re-enforced when cultivated under increased light/iron conditions and the new bulk community was diatom dominated. Incubations also revealed that Phaeocystis antarctica acclimated its pigment ratios to function more efficiently within different light and iron conditions and that community compositions in the Antarctic zone depend more on iron availability than that of the Polar Frontal zone. We conclude that both light and iron are significant controls on the phytoplankton community and that their effects varies regionally. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.