Variabilité hydrologique et biologique du golfe du Lion. II. Productivité sur le bord interne du courant

Abstract

Hydrological and biological variability in the Gulf of Lions. II. Productivity on the inner edge of the North Mediterranean Current. An estimation of the annual productivity in the Gulf of Lions has been made in the O-100 m layer using a Let-Go system, with monthly measurements at a fixed station. A value of I40 to 150 g mm2 a-' of C is found, of which around 75 % occurs in the upper 50 m. The seasonal production is described according to three distinct patterns during the two hydrological seasons: (1) variable production in winter; (2) surface bloom in late winter; (3) homogeneous and mean production in summer with a clear Deep Chlorophyll Maximum. The hydrological winter phase represented 60 % of total annual production. The seasonal duality of the hydrodynamic system and the mesoscale variations of the Northern Mediterranean Current account for the variability and the evolution of the three production patterns. 0 Elsevier, Paris primary production / budget / nitrate / chlorophyll / seasonal cycle Resume-La productivite annuelle du golfe du Lion a CtC estimee dans la couche O-100 m a l'aide d'un systeme Let-Go, par des mesures mensuelles a une station fixe. Une valeur de 140 a 150 g m-' a-' de C est obtenue, avec une contribution de 75 % pour la couche O-50 m. Le systeme productif saisonnier est decrit selon trois situations de base s'inscrivant dans deux saisons hydrologiques : (1) production variable en hiver ; (2) efflorescence algale en surface a la fin de la saison hydrologique hivernale ; (3) production homogbne et moyenne durant I'&&, avec presence d'un Maximum Profond de Chlorophylle. La saison hydrologique hivernale participe pour 60 % au bilan annuel total de carbone. La dualite saisonniere de l'hydrodynamisme et les variations a mesoechelle du Courant Nord MCditerranCen expliquent la variabilite et l'evolution des trois situations de base. 0 Elsevier, Paris production primaire 1 bilan / nitrate I chlorophylle / cycle saisonnier

Plankton in the open Mediterranean Sea: a review

“…Estimates from in situ incubations in previous decades were as low as 80-90 g C m −2 y −1 (Sournia, 1973). More recent measurements get closer to satellite-based estimates, e.g., in the Gulf of Lion (140-150 g C m −2 y −1 , Conan et al, 1998), but remain consistently lower in other areas such as the Cretan Sea (59 g C m −2 y −1 , Psarra et al, 2000). A clear eastward reduction in primary production was reported in the (May-June 1996).…”

Seasonal variability and export of dissolved organic nitrogen in the northwestern Mediterranean Sea

“…Deep mixing events occurring at the end of winter (February–March) when the temperature of the water column is homogeneous, result in movement of nutrient‐rich water into the euphotic zone. The quantity of nutrient input to the euphotic zone (higher in January 1994 than in February 1993; Figure 3), depends on the intensity of winter mixing due to the prevailing meteorological conditions, i.e., stronger northwest wind [ Conan et al , 1998]. The slight increase observed in total nitrogen (Table 2) is linked to the stronger winter convection in 1994 than in 1993, which brings dense water richer in nutrients closer to the surface.…”

“…We have selected eight representative cruises obtained at a station (42°50,0′ N; 05°12,5′ E) located 60 km off Marseille (Figure 1). This site corresponds to the outer edge of the northern Mediterranean Current (previously named Liguro‐Provencal Current) and is representative of the northwestern Mediterranean system which is influenced by (MAW) Modified Atlantic Water [ Conan and Millot , 1995; Conan et al , 1998].…”

“…Chlorophyll concentrations were determined by fluorimetry according to Herbland et al [1985]. Measurements of primary production were carried out at 43°05,0′ N; 05°12,5′ E (Figure 1) by short (4 h) in situ 14 C incubations (between 10 a.m. and 2 p.m.) with a new semiautomatic apparatus “Let‐go” [ Conan , 1996; Conan et al , 1998]. Carbon assimilation rates (PP) were corrected for dark uptake and calculated from the following equation: where dpm e , dpm b and dpm T are dpm of light bottles, dark bottles and total added activity respectively, V p and V f are the volume of tracer addition (250 μl) and of filtered seawater respectively, 1.05 is the isotopic fractionation factor between 12 C and 14 C, W is the total concentration of carbonates (∼27000 mg m −3 ) and T is the duration of incubation.…”

The characterisation and summer distribution of ultraphytoplankton in the Gulf of Gabès (Eastern Mediterranean Sea, Tunisia) by using flow cytometry

“…The Eastern Mediterranean Basin is the most oligotrophic region in the Mediterranean Sea (Berman et al, 1984;Krom et al, 2003Krom et al, , 2005, whereas the western basin is mesotrophic to oligotrophic, depending on season (Minas et al, 1988;Conan et al, 1998). Consequently, chl a concentrations do not usually exceed 0.5 mg dm À 3 in the eastern Mediterranean Basin (Yacobi et al, 1995;Gotsis-Skretas et al, 1999), and this is predominantly picophytoplankton (60%) reaching 80% in some places (see a review in Siokou-Frangou et al, 2010 and references herein).…”