Size-fractionated phytoplankton carboxylase activities in the Indian sector of the Southern Ocean

• Published in: Journal of Plankton Research
• Main Authors: Fouilland, E, Courties, C, Descolas-gros, C
• Format: Text
• Language: English
• Published: Oxford Univ Press 2000
• Subjects: envir; geo; Indian; Kerguelen; Kerguelen Islands; Southern Ocean
• Online Access: https://doi.org/10.1093/plankt/22.6.1185; https://archimer.ifremer.fr/doc/00220/33126/31651.pdf; https://archimer.ifremer.fr/doc/00220/33126/

During the ANTARES 3 cruise in the Indian sector of the Southern Ocean in October-November 1995, the surface waters of Kerguelen Islands plume, and the surface and deeper waters (30-60 m) along a transect on 62 degrees E from 48 degrees 36'8 to the ice edge (58 degrees 50'S), were sampled. The phytoplankton community was size-fractionated (2 mu m) and cell numbers, chlorophyll biomass and carbon assimilation, through Rubisco and beta-carboxylase activities, were characterized. The highest contribution of 2 mu m. The mixotrophic capacity of these small cells is proposed. From sampling stations of the Kerguelen plume, a relationship was observed between the Rubisco activity per picophytoplankton cell and apparent cell size, which varied with the sampled water masses. Moreover, a depth-dependent photoperiodicity of Rubisco activity per cell for <2 mu m phytoplankton was observed during the day/night cycle in the POOZ. In the near ice zone, a physiological change in picophytoplankton cells favouring phosphoenolpyruvate carboxykinase (PEPCK) activity was reported. A species succession, or an adaptation to unfavourable environmental conditions such as low temperature and/or available irradiance levels, may have provoked this change. The high contribution of picophytoplankton to the total biomass, and its high CO2 fixation capacity via autotrophy and mixotrophy, emphasize the strong regeneration of organic materials in the euphotic layer in the Southern Ocean.