Christophe Migon

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

Abstract Estimates of atmospheric inputs to the Mediterranean 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 even dominant (>80%) contribution to sediments in the offshore waters of the entire Mediterranean 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 Mediterranean and northern Adriatic indicate an even greater proportions 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 zinc and 15 to 30 times more important for lead 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 episodic 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 Mediterranean through direct sampling of the ocean and atmosphere before and after such events is therefore highly recommended.

Measurement of trace metal wet, dry and total atmospheric fluxes over the Ligurian Sea

Abstract An assessment of atmospheric inputs to the Ligurian Sea is reported here, including both wet and dry deposition. In order to evaluate the respective impact of the two contributions, a new sampling methodology was deployed at Cap Ferrat, on the French Ligurian coast. A receptacle was filled up with acidified water and acted as a trap for the total fallout. In parallel, rain water and aerosols were collected. Total fluxes: 0.18, 0.35, 6.0, 3.7, 8.6 and 220 μ m−2d−1 and wet fluxes: 0.09, 0.09, 1.6, 1.9, 1.6 and 106 μg m−2 d−1 were measured for Cd, Co, Cu, Ni, Pb and Zn, respectively. Using this database, dry fluxes were then calculated (0.09, 0.26, 4.4, 1.8, 7.0 and 114 μg m−2 d−1 for Cd, Co, Cu, Ni, Pb and Zn, respectively) and dry deposition velocities as well (0.4, 2.3, 1.2, 1.2, 0.2 and 4.4 cm s−1 for Cd, Co, Cu, Ni, Pb and Zn, respectively). Yearly inputs to the Ligurian Sea were also calculated for each metal.

Evaluation of total atmospheric deposition of Pb, Cd, Cu and Zn to the Ligurian Sea

The input of toxic metals through rainfall and dry deposition to the Ligurian Sea was measured over a period of 2 years (1986 and 1987) at the atmospheric sampling station situated at the Cap Ferrat meteorological base, on the French Mediterranean coast. Lead, Cd, Cu and Zn were analyzed by graphite furnace atomic absorption spectrophotometry and differential pulse anodic stripping voltammetry in order to calculate mean wet and dry atmospheric fluxes. The total fluxes determined were 3.3–18, 173.5 × 10−3, 1.85 and 9 kg km−2 year−1 for Pb, Cd, Cu and Zn, respectively, and the dry contribution appears to be very different from Cd (2%) to Pb(9–83%). Ligarian atmospheric fluxes are compared with those of other marine areas and show typical mediterranean levels. A mean yearly atmospheric input is calculated for each metal (175–950, 9.2, 98 and 480 tonnes (t) for Pb, Cd, Cu and Zn respectively) and compared with reverine loadings. In this part of the Mediterranean Sea, atmospheric inputs are far higher than those of rivers, especially in the case of Pb. The impact of atmospheric deposition on trace metal levels in Ligurian waters was also studied. The increase of metal concentrations in seawater presented in this work represents a mean situation, but much higher variations could be observed over a shorter scale of time and space, particularly in the case of Pb.

Separation of anthropogenic and natural emissions of particulate heavy metals in the western Mediterranean atmosphere

Abstract Measurements of atmospheric particulate matter often include both natural and anthropogenic aerosols. The method proposed here allows the two contributions to be separated, and then, to be estimated. Sampling was carried out at Cape Ferrat, on the southeastern coast of France, during 1986 and 1987. The concentrations of Pb, Cu, Zn and Cd were measured using flameless atomic absorption spectrophotometry. The concentration data allowed us to establish, for each metal, an experimental probability density function, which was numerically analyzed. The numerical process is described in detail. The results show a good agreement between the calculated natural background aerosol at Cape Ferrat and natural concentration levels measured in several remote locations. Differences are explainable by the nature of the environment. Anthropogenic emissions are very high compared with natural inputs, because most of the airborne heavy metals in the western Mediterranean arise from human activities.

Evolution of atmospheric lead over the northwestern Mediterranean between 1986 and 1992

Abstract The use of lead as an additive in petrol decreased in Europe from the 1970s and particularly from 1988 in France. It is attempted in this paper to evaluate the impact of such a decrease on a northwestern Mediterranean coastal environment. The atmospheric Pb concentrations measured at Cap Ferrat in 1986 and 1987 are compared with the 1991–1992 results (aerosol + rainwater) obtained at the same sampling site. The 50% decrease in the leaded gasoline consumption is expressed by Pb levels reduced of 24 and 30% in aerosol and rainwater, respectively. This decrease of Pb concentrations in the atmospheric aerosol is up to 2-fold higher in urban areas, where airborne Pb is almost totally due to automotive exhaust. Indeed, most of anthropogenic Pb should deposit close to its emission area.

Trace metal concentrations in the North-western Mediterranean atmospheric aerosol between 1986 and 2008: Seasonal patterns and decadal trends

Climatic and anthropogenic changes are able to engender modifications in the aerosol composition at different geographical and temporal scales. The present study addresses this question for the trace metal concentrations (TM=Al, Fe, Mn, Co, Ni, Cu, Pb, Cd and Zn) of aerosol from the North-western Mediterranean coast of France (Cap Ferrat, nearby Nice) between 1986 and 2008. From seasonal variations (2006-08) and decadal trends (1986-2008) of TM concentrations, three groups of elements can be distinguished. They consist of different aerosol sources: crustal-derived elements (Al, Fe, Mn and Co), trace metals of anthropogenic origin (Pb, Cd and Zn) and a third, intermediate, group of trace metals that presented both anthropogenic and natural/crustal influences (Ni and Cu). Reproducible seasonal patterns were observed for crustal and intermediate elements with highest concentrations between May and November, while anthropogenic trace metals did not show a pronounced seasonal cycle. Nevertheless, highest concentrations of anthropogenic trace metals occurred mostly in autumn/winter. Aerosol concentrations of anthropogenic TMs decreased remarkably over the last two decades, while crustal trace metals did not show any evolution. Nickel and copper aerosol concentrations remained constant, as well. Lead concentrations decreased from 1986 (29.34 ng m(-3)) to 2008 (3.33 ng m(-3)), overall by 90%. Cadmium and zinc aerosol concentrations decreased by 66 and 54%, respectively, between 1998 and 2006-08, from 0.27 to 0.09 ng m(-3) and from 23.9 to 10.9 ng m(-3), respectively. These findings demonstrate the response of the atmospheric environment to the implementation of antipollution policies. Possible changes of trace metal emissions sources and local influences are discussed.

Observing mixed layer depth, nitrate and chlorophyll concentrations in the northwestern Mediterranean: A combined satellite and NO3 profiling floats experiment

Two profiling floats, equipped with nitrate concentration sensors were deployed in the northwestern Mediterranean from summer 2012 to summer 2013. Satellite ocean color data were extracted to evaluate surface chlorophyll concentration at float locations. Time series of mixed layer depths and nitrate and chlorophyll concentrations were analyzed to characterize the interplay between the physical-chemical and biological dynamics in the area. Deep convection (mixed layer depth > 1000 m) was observed in January–February, although high-nitrate surface concentrations could be already observed in December. Chlorophyll increase is observed since December, although high values were observed only in March. The early nitrate availability in subsurface layers, which is likely due to the permanent cyclonic circulation of the area, appears to drive the bloom onset. The additional nitrate supply associated to the deep convection events, although strengthening the overall nitrate uptake, seems decoupled of the December increase of chlorophyll.

Atmospheric deposition of metallic pollutants over the Ligurian Sea: labile and residual inputs.

Atmospheric fluxes of six trace metals (Cd, Cr, Cu, Ni, Pb and Zn) with Al as a crustal reference were measured at Cap Ferrat (French Riviera) between February 1997 and July 1998. An original sampling protocol enabled the separation of labile (seawater at pH 2) and residual fractions in the total atmospheric input. Median acid-labile fractions were 91%, 69%, 83%, 84%, 97% and 98% of the total for Cd, Cr, Cu, Ni, Pb and Zn, respectively. Under the conditions used, lability of individual metals is related to the anthropogenic component of the samples. Enrichment factors and anthropogenic fraction are estimated for each metal. Some interannual changes are investigated (Pb, Zn). The observed increase of Zn inputs may be linked to local input from the Nice district waste plant (commissioned in 1988), 6.5 km away.

Impact of arsenic and antimony contamination on benthic invertebrates in a minor Corsican river

The chemical and biological characteristics of a Corsican river that drains contaminated waters and sediment from an abandoned realgar mine were studied. The concentrations of pollutants such as As and Sb were found to be notably high. For example, in the Presa River, downstream the realgar mine, the mean As concentrations in the water and in the sediment were 3010 μg 1-1 and 9450 μg g-1 respectively. Species richness and abundance of benthic invertebrates decreased downstream the As mine. The disappearance of oligochaetes, leeches and a rarity of mayfly populations have been evidenced. On the contrary, a large increase in species belonging to stoneflies and gastropods was found. Some species like Baetis cyrneus, Ephemerella ignita, Sericostoma clypeatum and Ibisia marginata were more sensitive to As and Sb concentrations while others species like Ancylus fluviatilis, Isoperla insularis, Hydropsyche cyrnotica, Caenis luctuosa and Silonella aurata were less sensitive. The benthic invertebrates show different reactions in this contaminated environment, which could be explained by their feeding behaviours and certain morphological characteristics.

Riverine and atmospheric inputs of heavy metals to the ligurian sea

Abstract The aim of this paper is to provide an estimation of the riverine and atmospheric contributions of Pb, Cd, Cu and Zn supply to the Ligurian Sea. Riverine dat come from Arno, Var and Roya rivers and atmospheric data come from total deposition-sampling on the southeastern coast of France. Taking into account the behaviour of each metal in estuarine conditions (i.e. the net dissolved metal inputs from rivers to the sea), the atmospheric inputs are always higher, with the following ratios: 195–1055, 3.3–11.5, 16.3–32.6 and 7.4–160 for Pb, Cd, Cu and Zn, respectively. Here an interpretation of the preponderence of the atmospheric factor, is proposed. Considering that riverine metal fluxes are far lower than atmospheric metal fluxes over the associated watershed surface area, it is suggested that atmospheric deposition over the watershed is the major contribution of riverine pollutant fluxes and most of this atmospheric deposition is lost into soils and riverine sediments. This assumption could be evended to the whole western Mediterranean basin whose surface area is larger than that of its associated watershed.