The role of atmospheric deposition in the biogeochemistry of the Mediterranean Sea

Estimates of atmospheric inputs to the Mediterranean (MED) and some coastal areas are reviewed, and uncertainities in these estimates considered. Both the magnitude and the mineralogical composition of atmospheric dust inputs indicate that eolian deposition is an important (50%) or prevailing (>80%) contribution to sediments in the offshore waters of the entire Mediterranean (MED) basin. Model data for trace metals and nutrients indicate that the atmosphere delivers more than half the lead and nitrogen, one-third of total phosphorus, and 10% of the zinc entering the entire basin. Measured data in sub-basins, such as the north-western MED and northern Adriatic indicate an even greater proportion of atmospheric versus riverine inputs. When dissolved fluxes are compared (the form most likely to impinge on surface water biogeochemical cycles), the atmosphere is found to be 5 to 50 times more important than rivers for dissolved Zn and 15 to 30 times more important for Pb fluxes. Neglecting co-limitation by other nutrients, new production supported by atmospheric nitrogen deposition ranges from 2-4 g C m-2 yr-1, whereas atmospheric phosphorus deposition appears to support less than 1 g C m-2 yr-1. In spite of the apparently small contribution of atmospheric deposition to overall production in the basin it has been suggested that certain episodes of phytoplankton blooms are triggered by atmospheric deposition of N, P or Fe. Future studies are needed to clarify the extent and causal links between these episodic blooms and atmospheric/oceanographic forcing functions. A scientific program aimed at elucidating the possible biogeochemical effects of Saharan outbreaks in the MED through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended

Chemical characterization of the Saharan end-member : some biogeochemical implications for the western Mediterranean Sea.

International audienceTwo types of samples were used to chemically characterize the Saharan end-member: fine fractions of surface soil samples collected in Northern Africa and particulate phases of typical Saharan rains. Since the concentrations measured in the particulate phase of the Saharan rains were corrected from the dissolution losses in rainwater, these particles were considered to be representative of the transported Saharan dust before being blended into rainwater. Al, Fe, P, and Pb were analyzed: except for lead, the chemical composition of the transported Saharan dust was more homogeneous than the composition of individual soils. As confirmed by the air mass back trajectories, the higher level of homogeneity of the aerosol is partly due to the fact that a dust event affects a large area of the Saharan desert, and the composition of the particles reflects the average composition of the eroded areas. Pb concentration in the transported dust reflected an anthropogenic fraction. By using Pb/Al measurements from the soils it was shown that a typical Saharan rain event with no mixing with air masses from Europe appears to be very rare in the Mediterranean environment. The following values are proposed to characterize the Saharan dust end-member: Al (%) = 7.09 ± 0.79; Fe (%) = 4.45 ± 0.49; P (%) = 0.082 ± 0.011; Pb (ppm) = 24 ± 9. This study suggests that the [element/Al or Fe)] ratio is also useful to characterize the Saharan end-member as they are very homogeneous for the two sample types. Saharan dust represents a potential source of nutrients (P, Fe) for the Mediterranean water. Indeed, it accounts for ∼30–40% of the total atmospheric flux of phosphorus in the western Mediterranean, and it governs the biogeochemical cycle of iron being the main source of dissolved iron in the western Mediterranean waters

Biomass burning as a source of dissolved iron to the open ocean?

International audienceWhile the Mediterranean region is typified by frequent summer fires, the 2003 heat wave that hit Europe, and France in particular, made this season longer causing devastating fires. Aerosol sampling performed in the French Riviera between August and September 2003 indicated that iron concentrations in 2003 were significantly higher than in previous years. Continuous pyrogenic emissions are suspected to be the cause of high Fe concentrations. When these particles were dissolved in seawater, 2% of the total iron content was found in solution. This amount could be significant for the water column on a regional scale. Indeed, these fires might explain the observed dissolved iron enrichment of the surface mixed layer (+0.4 nM) measured in the Ligurian Sea during August. In contrast to a locally significant effect, pyrogenic inputs have little impact on the global Fe budget since they represent at most 10% of desert dust inputs

Rainwater chemistry at a Mediterranean inland station (Avignon, France): Local contribution versus long-range supply

International audienceIn order to investigate the role of local contribution versus long-range transport in the rainwater chemistry at a site in the North-western Mediterranean area, we collected 90 daily wet samples, 75 dry samples (corresponding to bulk sampling during dry periods) and 102 sequential wet sub-samples from October 1997 to March 1999. Major ions were analyzed (Mg2+, Ca2+, Na+, K+, Cl−, SO42−, NO3−, NH4+, HCO3−) along with the determination of pH and electrical conductivity. To discriminate the fraction of components supplied by long- and medium-range transport from that derived from local scavenging, a classification of precipitation chemistry according to air masses back trajectories and sources has been established. Three different origins were identified: (1) a Western one associated with high amount of rainfall and an equivalent contribution of terrestrial, marine and anthropogenic components, (2) a Northern and North-eastern origin characterized by low rainfall heights and a high load in anthropogenic and terrestrial components, (3) a Southern origin which presented the highest concentration in sea-salt components and a high participation of anthropogenic components. Determination of the local contribution has been achieved through the characterization of dry deposition rates and the investigation of the evolution of rain chemistry during events. As only 21 to 32% of the total concentration is removed in the first fraction, it appeared that the below-cloud scavenging process does not dominate the removal of atmospheric components in the region. The evolution of the rain chemistry during an event is perturbed by increases of concentrations that could be due either to long-range inputs (of humid air parcels coming from the near Mediterranean Sea or occurrence of Saharan dust) or to the scavenging of local sources of pollutants and terrestrial materia

Présence du genre Aphanius Nardo, famille des Cyprinodontidae, dans le Miocène du Bassin de Francardo-Ponte Leccia (Corse)

Among the four Corsican Miocene sedimentary basins, the Francardo-Ponte Leccia basin is the only one lying in the centre of the island. With a North-South axis, it is located at the frontier between the Hercynian and the Alpine parts of Corsica. The sedimentation is controlled by distensional and transverse tectonics. Three formations are distinguished which are, from the bottom to the top, and from the South to the North the Ortone, the Taverna and the Francardo formations. The Ortone and Francardo formations are continental with conglomeratic deposits of debris flows, alluvial fan and fluviatile types. The Taverna formation, made of marls, silts and sands deposits followed by sandstones and conglomerates, is a lagu-nal-marine in origin. Hie studied fish and scales were found at the top of the marl-silty levels which, according to the microfauna, are Middle Burdigalian age. The fish skeleton belongs to the Cyprinodontidae and more precisely to the genus Aphanius Nardo, which characterize brackish environnement in the Recent Mediterranean area. This is the first reference of a Teleostean fish in the Corsican Miocene.Parmi les bassins miocènes de Corse, le bassin de Francaido-Ponte Leccia occupe une position géographique centrale. Il s'agit d'un bas¬ sin allongé selon la direction Nord-Sud, dans la zone de contact entre la Corse hercynienne et la Corse alpine. Le remplissage sédimentaire est constitué par trois formations, limitées par des discontinuités, contrôlées par une tectonique distensive et décrochante. On distingue du bas vers le haut et du Nord au Sud : les formations de l'Ortone, de Tavema et de Francardo. Les formations de l'Ortone et de Francardo sont formées par des ensembles conglomératiques principalement de type cône alluvial et fluviatile. La formation de Tavema est caractérisée par une série mamo-silto-gréseuse se terminant par des conglo¬ mérats et des grès. C'est dans cette formation, soumise à des influences marines qu'un poisson a été découvert. Il a été récolté, ainsi que des écailles, entre des marnes silto-gréseuses franchement marines, datées du Burdigalien moyen, et les conglomérats susja-cents. 11 s'agit d'un poisson Cyprinodontidae appartenant au genre Aphanius Nardo dont les espèces actuelles peuplent assentiellement des étendues d'eau à salinité variable. Les restes de macrofaune et de macroflore associés à Aphanius Nardo témoignent d'un environnement lagunaire. Cette découverte apporte ainsi des informations paléoécologiques utilisables pour l'interprétation des conditions de dépôt de la formation de Tavema.Cubells J.F., Ferrandini Jean, Maurel-Ferrandini Michelle, Gaudant Jean, Loÿe-Pilot Marie-Dominique. Présence du genre Aphanius Nardo, famille des Cyprinodontidae, dans le Miocène du Bassin de Francardo-Ponte Leccia (Corse). In: Géologie Méditerranéenne. Tome 21, numéro 1-2, 1994. Récifs et plates-formes carbonatées miocènes de Méditerranée / Miocene reefs and carbonate platforms of the Mediterranean. Interim colloquium R.C.M.N.S. (Marseille 3-6 mai 1994) sous la direction de Jean-Paul Saint-Martin et Jean-Jacques Cornée. pp. 19-24

Carte géol. France (1/50 000), feuille Sotta-Bonifacio-Santa-Teresa-di-Gallura (1127). Orléans : BRGM. Notice explicative

Carte géol. France (1/50 000), feuille Sotta-Bonifacio-Santa-Teresa-di-Gallura (1127). Orléans : BRGM. Notice explicativ

Marine ecosystems’ responses to climatic and anthropogenic forcings in the Mediterranean

International audienceThe semi-enclosed nature of the Mediterranean Sea, together with its smaller inertia due to the relative short residence time of its water masses, make it highly reactive to external forcings, in particular variations of water, energy and matter fluxes at the interfaces. This region, which has been identified as a “hotspot” for climate change, is therefore expected to experience environmental impacts that are considerably greater than those in many other places around the world. These natural pressures interact with the increasing demographic and economic developments occurring heterogeneously in the coastal zone, making the Mediterranean even more sensitive. This review paper aims to provide a review of the state of current functioning and responses of Mediterranean marine biogeochemical cycles and ecosystems with respect to key natural and anthropogenic drivers and to consider the ecosystems’ responses to likely changes in physical, chemical and socio-economical forcings induced by global change and by growing anthropogenic pressure at the regional scale. The current knowledge on and expected changes due to single forcing (hydrodynamics, solar radiation, temperature and acidification, chemical contaminants) and combined forcing (nutrient sources and stoichiometry, extreme events) affecting the biogeochemical fluxes and ecosystem functioning are explored. Expected changes in biodiversity resulting from the combined action of the different forcings are proposed. Finally, modeling capabilities and necessity for modeling are presented. A synthesis of our current knowledge of expected changes is proposed, highlighting relevant questions for the future of the Mediterranean ecosystems that are current research priorities for the scientific community. Finally, we discuss how these priorities can be approached by national and international multi-disciplinary research, which should be implemented on several levels, including observational studies and modeling at different temporal and spatial scales