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Seasonal and interannual dynamics of nutrients and phytoplankton pigments in the western Mediterranean Sea at the DYFAMED time-series station (1991-1999)
Marty, J.-C.; Chiavérini, J.; Pizay, M.D.; Avril, B. (2002). Seasonal and interannual dynamics of nutrients and phytoplankton pigments in the western Mediterranean Sea at the DYFAMED time-series station (1991-1999). Deep-Sea Res., Part 2, Top. Stud. Oceanogr. 49(11): 1965-1985
In: Deep-Sea Research, Part II. Topical Studies in Oceanography. Pergamon: Oxford. ISSN 0967-0645, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Marty, J.-C.
  • Chiavérini, J.
  • Pizay, M.D.
  • Avril, B., more

Abstract
    The phytoplankton dynamics in the western Mediterranean Sea has been studied at the DYFAMED (France JGOFS) time-series station from 1991 to 1999 by means of an analysis of monthly pigment profiles in the 0-200-m layer. The site (43degrees25'N, 7degrees52'E) is located in the central zone of the Ligurian Sea, NW-Mediterranean Sea, and is protected from coastal inputs by the presence of Ligurian current flowing along the coast. The seasonal hydrological regime varies from winter mixing (January-February) to strong thermal stratification in summer and fall. Nutrients are depleted in the surface layer during summer oligotrophic conditions and re-injected to the surface layer during winter mixing. The nitrate-to-phosphate ratio is about 20 in deep waters, which indicates a general tendency to P-limitation. Nevertheless our 9-year study indicates that N/P ratio in surface layer is always higher than 20 (up to 60) during oligotrophic period and generally lower than 20 during the rest of the year. This indicates a probable shift from N-limitation in winter to P-limitation in summer. Seasonal variations of phytoplankton dynamics have been characterized using the HPLC pigment approach, and related to hydrological conditions and distribution of nutrients. The 0-200 m integrated chlorophyll a during the 9-year study is highly variable (from 12 to 230 mg m(-2)). The phytoplankton biomass is dominated by 19'-hexanoyloxyfucoxanthin-containing algae all the year round, but the relative abundance of the characteristic populations with respect to total biomass indicates a seasonal succession. The contribution of diatoms to biomass, as inferred from facoxanthin, is maximal in January or February and is followed 1 month later by 19'-hexanoyloxyfiicoxanthin-containing nano flagellates. The ratio of zeaxanthin (associated to cyanobacteria) to chlorophyll a is highest at the beginning of the stratified period, just before maximal contribution of divinyl-chlorophyll a (prochlorophytes) to biomass. There was a general increase in total phytoplankton biomass during the 9-year study. This increase seems mainly due to small-sized phytoplankton as a specific response to the lengthening of the summer stratification period favoring the growth of species supporting the regenerated production.

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