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

• Main Authors: Eric Fouill, Claude Courties, Chantal Descolas-gros
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Indian; Kerguelen; Kerguelen Islands; Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1033.4657; http://plankt.oxfordjournals.org/content/22/6/1185.full.pdf

Abstract. 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°E from 48°36S to the ice edge (58°50S), were sampled. The phytoplankton community was size-fractionated (2 µm) and cell numbers, chlorophyll biomass and carbon assimilation, through Rubisco and -carboxylase activities, were characterized. The highest contribution of <2 µm cells to total biomass and total Rubisco activity was reported in the waters of the Permanent Open Ocean Zone (POOZ) located between 52°S and 55°S along 62°E. In this zone, the picophytoplankton contributed from 26 to 50 % of the total chlorophyll (a + b + c) with an average of 0.09 ± 0.02 µg Chl l–1 for <2 µm cells. Picophytoplankton also contributed 36 to 64 % of the total Rubisco activity, with an average of 0.80 ± 0.30 mg C mg Chl a–1 h–1 for <2 µm cells. The picophyto-plankton cells had a higher -carboxylase activity than larger cells>2 µm. 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 µm phytoplankton was observed during the day/night cycle in the POOZ. In the near