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
Transfer processes from a eutrophic ecosystem, the river Rhone, to an oligotrophic environment, the north-west Mediterranean Sea, were studied during the winter period, when inputs of dissolved and particulate matter are at their highest.During a cruise carried out in February 1987, salinity, temperature, turbidity, nutrients, pigments, suspended particulate matter and particulate carbon and nitrogen were measured in surface and subsurface waters near the Rhone outlet.For most of the parameters the results show that during this period a simple dilution process occurs in the river plume of the RhBne without adsorption, desorption, precipitation or biological uptake, contrary to recordings for some other rivers. All the nutrients discharged into the sea by the Rh6ne are available for utilization by marine phytoplankters.
Hydrological and biological variability in the Gulf of Lions. I. Nitrogen fluxes and potential productivity. A monthly time-series of the seasonal evolution of the North Mediterranean Current (NMC) and of nitrogen flux across a transect (5" 12'5 E between 43" 10'N and 42" 50'N) at the entrance of the Gulf of Lions was carried out over two years. The NMC exhibited two distinct structures: a winter structure (from November to May) characterised by strong mesoscale and interannual variations in which the current was 20 to 30 km width, about 400 m depth and velocity scaled between 5 and more than 40 cm s-'; and a summer structure (from May to November) which was less sensitive to mesoscale variations but showing large interannual variability. The current was located more offshore, was wider and shallower than the one in winter and velocity remained below 20 cm s-'. Meteorological conditions, frontal structures on both sides of the NMC, coastal upwelling and continental inputs explained the observed mesoscale discrepancies between water flux and nitrogen transport. Nitrogen input from the general circulation across the prospected transect is estimated at 187 + 20 kTa-' in the O-200 m layer, with a distribution of 39 % nitrate, 6 % particulate nitrogen and 55 % dissolved organic nitrogen. Nitrate input (25 + 3 kT a-') in the O-l 00 m upper layer could sustain more than one third of the potential new production in the Gulf of Lions. 0 Elsevier. Paris hydrology I mesoscale variability I nitrogen I flux I budget R&urn4-Un suivi mensuel de l'evolution saisonniere du Courant Nord Mtditerraneen (CNM) et des flux en azote a travers une radiale (5" 12'5 E entre 43" 1 O'N et 42" 50'N) a CtC realise, & l'entrte du golfe du Lion, sur une periode de deux ans. Le CNM est decrit selon deux structures disdnctes. Une structure hivernale (de novembre a mai) caracterisee par de fortes variations a m&o-echelle et interannuelles ; la veine de courant est large de 20 a 30 km et profonde d'environ 400 m, avec des vitesses comprises entre 5 et plus de 40 cm s-'. Une structure estivale (entre mai et novembre) moins sensible aux variations a m&o-echelle mais presentant une forte variabilite interannuelle ; la veine est alors plus hauturiere, plus large et moins profonde qu'en hiver. les vitesses restant generalement inferieures a 20 cm s-'. Les conditions meteorologiyues, la presence de zones frontales sur les bords interne et externe du CNM, les phtnomenes d'upweffing &tier et d'apports continentaux permettent d'expliquer les decouplages observes entre les flux en eau et en azote a travers la radiale. Les apports en azote par la circulation g&r&ale a travers la radiale sont estimes a 187 rt 20 kT a-' dans la couche O-200 m, et se repartissent en 39 % de nitrate, 6 % d'azote particulaire et 55 % d'azote organique dissous. Les apports de nitrate dans la couche superficielle O-100 m (25 + 3 kTa-') pourraient etre a l'origine de pres d'un tiers de la production nouvelle potentielle du golfe du Lion. 0 Elsevier, Paris
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