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

Atmospheric fluxes of ²¹⁰Pb to the western Mediterranean Sea and the Saharan dust influence

Pb 210 is a well known tracer of particle dynamics in the marine environment. Geochemical models partially rely on the knowledge of its atmospheric input. Unfortunately, this is poorly known in the western Mediterranean Sea, especially regarding long-term records. In this work we have evaluated the ²¹⁰Pb annual atmospheric flux to this region from the analysis of 12 soil cores collected from coastal and island sites and total atmospheric deposition collected in Corsica during 1 year. The ²¹⁰Pb fluxes ranged from 34 ± 3 to 121 ± 12 Bq m¯² yr¯¹ , with an average of 75 Bq m¯² yr¯¹, and were strongly correlated (R²= 0.95) with mean annual rainfall. This provides the possibility to determine ²¹⁰Pb fluxes in a given location if the mean annual rainfall is well known, a useful outcome for both marine biogeochemical and soil erosion studies in this region. We have also estimated the mean annual atmospheric flux of ²¹⁰Pb due to Saharan dust events registered in total deposition north of Barcelona during the last 17 years, yielding a value of 20 Bq m¯² yr¯¹ . This flux represents a fraction of about 16% of the total atmospheric deposition of ²¹⁰Pb in this area, but it could be up to 50% in sites with lower rainfall

Role of desert aerosol in metal fluxes in the Mediterranean area.

Aerosols and precipitations collected over Sardinia are mainly controlled by two end-members: Saharan and European. European background aerosols in Sardinia show a 3 to 25-fold decrease in EFcrust values for Cd, Zn, Pb, and Cr compared with coastal stations in the Western Mediterranean. Partitioning of total atmospheric deposition between the soluble and the insoluble phases shows that Al, Si, Fe and Pb originating from the atmosphere are mostly in the insoluble form. For Ca, Cd, Cr metals the dissolved fraction represents 50-90 % of the total input. Aerosol dissolution experiments performed at particle concentrations ranging from 3 to 300 mg l-1 show Cd and Pb exhibiting low solubility at the high mass particle concentration. Solubility of Pb increases with the EFcrust values and the finest grain-size of the aerosols (<1µm), and is less affected by pH. Al and Fe solubilities appear to be mainly controlled by the particulate load. Dissolution of both metals decreases significantly from 30% (13 % for Fe) at aerosol loads lower than 5 mg l-1, to less than 1% for both metals, at total aerosol concentrations greater than 50 mg l-1, which are encountered during Saharan transport. Fluxes (dry +wet) of metals at Sardinia show that ~ 30% for Cd and Pb, to more than 80 % for Fe and Al are due to Saharan contribution

Climate change and Saharan dust drive recent cladoceran and primary production changes in remote alpine lakes of Sierra Nevada, Spain

Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll-a concentrations over the past ~150 years from high-resolution, welldated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll-a concentrations in recent decades indicate a regional-scale response to climate and Saharan dust deposition. Chlorophyll-a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake-specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, among others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in softwater, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystemsMinisterio de Educación y Ciencia (MEC), Grant/Award Number: AP2007-00352; Programa Nacional de Movilidad de Recursos Humanos de Investigaci on (MICINN); Ministerio de Medio Ambiente (MMA), Grant/Award Number: 87/2007; Ministerio de Econom ıa, Industria y Competitividad (MINECO), Grant/Award Number: CGL2011-23483; Natural Sciences and Engineering Research Council of Canad

Spatial variability of atmospheric fluxes of metals (Al, Fe, Cd, Zn and Pb) and phosphorus over the whole Mediterranean from a one-year monitoring experiment: Biogeochemical implications

International audienc

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