Rapid bacterial mineralization of organic carbon produced during a phytoplankton bloom induced by natural iron fertilization in the Soutern Ocean

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Obernosterer, Ingrid, Christaki, Urania, Lefèvre, Dominique, Catala, Philippe, van Wambeke, France, Lebaron, Philippe
• Other Authors: Laboratoire d'océanographie biologique de Banyuls (LOBB), Observatoire océanologique de Banyuls (OOB), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Ecosystèmes Littoraux et Cotiers, Université de Lille, Sciences et Technologies-Centre National de la Recherche Scientifique (CNRS), Hellenic Centre for Marine Research (HCMR), Laboratoire de MicrobiologiE de Géochimie et d'Ecologie Marines (LMGEM), Université de la Méditerranée - Aix-Marseille 2-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2008
• Subjects: Bacterial growth efficiency; Southern Ocean; Natural iron fertilization; Heterotrophic bacteria; High nucleic acid cells; bacterial respiration; [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; [SDV.EE.IEO]Life Sciences [q-bio]/Ecology; environment/Symbiosis; [SDV.MP.BAC]Life Sciences [q-bio]/Microbiology and Parasitology/Bacteriology; Kerguelen
• Online Access: https://hal.archives-ouvertes.fr/hal-00290755; https://hal.archives-ouvertes.fr/hal-00290755/document; https://hal.archives-ouvertes.fr/hal-00290755/file/Obernosterer%20et%20al%202008%20keopsII-for%20hal.pdf; https://doi.org/10.1016/j.dsr2.2007.12.005

The response of heterotrophic bacteria (Bacteria and Archaea) to the spring phytoplankton bloom that occurs annually above the Kerguelen Plateau (Southern Ocean) due to natural iron fertilization was investigated during the KErguelen Ocean and Plateau compared Study (KEOPS) cruise in January–February 2005. In surface waters (upper 100 m) in the core of the phytoplankton bloom, heterotrophic bacteria were, on an average, 3-fold more abundant and revealed rates of production ([3H] leucine incorporation) and respiration (<0.8 μm size fraction) that exceeded those in surrounding high-nutrient low-chlorophyll (HNLC) waters by factors of 6 and 5, respectively. These differences in bacterial metabolic activities were attributable to high-nucleic-acid-containing cells that dominated (≈80% of total cell abundance) the heterotrophic bacterial community associated with the phytoplankton bloom. Bacterial growth efficiencies varied between 14% and 20% inside the bloom and were <10% in HNLC waters. Results from bottle-incubation experiments performed at the bloom station indicated that iron had no direct but an indirect effect on heterotrophic bacterial activity, due to the stimulation by phytoplankton-derived dissolved organic matter. Within the Kerguelen bloom, bacterial carbon demand accounted for roughly 45% of gross community production. These results indicate that heterotrophic bacteria processed a significant portion of primary production, with most of it being rapidly respired.