Contrôle des variations à court terme de la production biologique de diméthylsulfure (DMS) en milieu marin

Authors: Merzouk, Anissa
Advisor: Levasseur, Maurice
Abstract: Dimethylsulfide (DMS) is a biogenic gas exerting a cooling effect on climate by promoting cloud formation, thus decreasing the amount of solar radiation entering the atmosphere. DMS is produced in the oceans from the degradation of dimethylsulfoniopropionate (DMSP) synthesized by marine phytoplankton. Some algal DMSP-producers have the capability to directly produce DMS, but a large part of the production of DMS is believed to occur indirectly, through the release of algal DMSP and its uptake and utilization by bacteria. DMS production represents less than 10% of the DMSP degraded by bacteria, which utilize it mainly as a source of sulfur. Short-term variations of the biological DMS production and its controlling factors were studied in the St. Lawrence Estuary, the northeast Pacific and the northwest Atlantic. In the St. Lawrence Estuary, DMSP and DMS concentrations exhibited large and rapid variations with maxima around noon and minima during the night. These variations were largely explained by the diurnal vertical migration of DMSP-rich dinoflagellates associated with an increased DMSP and DMS production under high solar irradiance during the day. In the NE Pacific, the low prevailing iron concentrations favoured a DMSP-rich algal community. The iron enrichment induced a decrease in DMS relative to non-enriched waters due to a change in the phytoplankton community toward DMSP-poor diatoms and an increase in the abundance and activity of bacteria. This growing bacterial community modified its DMSP utilization and produced little DMS. In the NO Atlantic, the decline of the diatom spring bloom was characterized by a decrease in DMSP concentrations in surface waters. DMSP consumption and DMS production by bacteria also rapidly decreased, probably because they satisfied their metabolic requirements with other organic substrates more readily available than DMSP. The pools and biological processes of the DMS(P) cycle vary at scales of hours and days. The study of these short-term variations is needed to accurately measure DMS production and to better assess its effect on climate.
Document Type: Thèse de doctorat
Issue Date: 2007
Open Access Date: 12 April 2018
Grantor: Université Laval
Collection:Thèses et mémoires

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