Roy Chester

A chemical technique for the separation of ferro-manganese minerals, carbonate minerals and adsorbed trace elements from pelagic sediments

Abstract In order to investigate the partitioning of trace elements in pelagic sediments various selective chemical techniques are examined, and a method is described which may be used to separate chemically those trace elements incorporated into pelagic sediments by ferro-manganese nodules, carbonate minerals (excluding dolomite) and by adsorption onto mineral surfaces. The investigated techniques are: those involving the use of acids (e.g., dilute acetic acid), those involving the use of reducing agents (e.g., 1M hydroxylamine hydrochloride) and those involving the use of both acids and reducing agents. The application of the technique described is illustrated by examining the partition of Ni and V in a pelagic sediment sample.

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.

The impact of desert dust across the Mediterranean

Preface. Modelling and Climate. Climate Modeling Over the Mediterranean Region: An Overview F. Giorgi. Modeling of Dust Processes for the Saharan and Mediterranean Area S. Nickovic. Quantitative Remote Sensing of African Dust Transport to the Mediterranean F. Dulac, et al. Model Components Necessary to Capture a Dust Plume Pattern Over the Mediterranean Sea M. Schulz, et al. The Preliminary Modeling Results of Saharan Dust Transport to the Mediterranean Sea and Europe S. Grigoryan, L. Erdman. Importance of the Source Term and the Size Distribution to Model the Mineral Dust Cycle Y. Balkanski, et al. The Effects of Desert Particles on Cloud and Rain Formation in the Eastern Mediterranean Z. Levin, E. Ganor. Application of a Lagrangian Model to the Study of the Atmospheric Fluxes to the Western Mediterranean M. Alarcon, et al. Atlantic Perturbations Deeply Penetrating the African Continent: Effects Over Saharan Regions and the Mediterranean Basin M. Conte, et al. Seasonal Distribution of the Boundary Layer Depths over the Mediterranean Basin U. Dayan, et al. Biomass Burning in North Africa and Its Possible Relationship to Climate Change in the Mediterranean Basin D.O. Suman. Modeling the Present and Last Glacial Maximum Transportation of Dust to the Arctic With an Extended Source Scheme K. Andersen, C. Genthon. Geology and Source Regions. Saharan Dust Transport Over the North Atlantic Ocean and Mediterranean: An Overview J.M. Prospero. Mineralogical Characterisation of Saharan Dust with a View to its Final Destination in Mediterranean Sediments E. Molinaroli. The Mineralogical and Chemical Properties and the Behaviour of the Eolian Saharan Dust over Israel E. Ganor, et al. Identification and Quantification of Dust Additions in Peri-Saharan Soils L. Hermann, et al. Sedimentological Characteristics of Saharan and Australian Dusts L. Kiefert, et al. Saharan Dust Input to the Western Mediterranean: An Eleven Years Record in Corsica M.D. Loye-Pilot, J.M. Martin. African Dust Over Northeastern Spain: Mineralogy and Source Regions A. Avila, et al. Saharan Aerosols: From the Soil to the Ocean C. Guieu, A.J. Thomas. Atmosphere-Ocean Mass Fluxes at Two Coastal Sites in Sardinia (39-41 N, 8-10 E) O. Le Bolloch, et al. Mineralogy and Source of High Altitude Glacial Deposits in the Western Alps: Clay Minerals as Saharan Dust Tracers L. Tomadin, et al. Grain Size Analysis of Aerosol and Rain Particles: A Methodological Comparison G. de Falco, et al. Aerobiological Results from the 1994 Cruise of the Urania (CNR) II P. Comtois, P. Mandrioli. Long-Range Transport of Biological Particles of Desert Origin: A Short Review M. Hjelmroos. Chemical Fluxes and Composition of the Atmosphere. The Influence of Saharan and Middle Eastern Desert-Derived Dust on the Trace Metal Composition of Mediterranean Aerosols and Rainwater: An Overview R. Chester, et al. Elemental Composition and Air Trajectories of African Dust Transported in Northern Italy P. Bonelli, et al. The Impact of Saharan Dust on Trace Metal Solubility in Rainwater in Sardinia, Italy F. Frau, et al. Northward Transport of Saharan Dust Recorded in a Deep Alpine Ice Core D. Wagenbach, et al. Estimating Dust Input to the Atlantic Ocean Using Surface Water Aluminium Concentrations C.I. Measures, E.T. Brown. Effect of Saharan Dust Transport on Ozone and Carbon Dioxide Concentration P. Bonasoni, et al. African Dust Influence on Rainwater on the Eastern Coast of Spain A. Carratala, et al. Trace Metal C

Saharan dust inputs to the western Mediterranean Sea: depositional patterns, geochemistry and sedimentological implications

Data are presented for a number of parameters for aerosols and rainwaters collected at a station on Sardinia. The findings are interpreted with special reference to Saharan dusts, and are compared to other data on these dusts obtained from a variety of sites around the Mediterranean Sea. At the Sardinia site the particle size distribution of the Saharan outbreaks exhibits a bimodal structure, the two modes being between 2 and 4 μm and 15 and 30 μm. The presence of giant particles strongly affects the deposition velocities of the Saharan aerosols. Source markers for the Saharan dusts are palygorskite, kaolinite, calcite, dolomite and rounded quartz grains. The input of Saharan dust has important effects on the chemistry of the Mediterranean aerosols. These include: (i) increases in the atmospheric concentrations and sea surface fluxes of crust-controlled trace metals (e.g. Al, Fe); (ii) decreases in the EFcrust values of non-crust-controlled trace metals (e.g. Cu, Zn and Pb) in the aerosols, and (iii) changes in the solid state speciation of Cu, Zn, and Pb, which decrease their solubilities in seawater. The Saharan dusts also affect the composition of rainwater by raising the pH, following the dissolution of calcium, and by decreasing the solubility of trace metals such as Cu, Zn and Pb. Wet deposition controls the flux of Saharan dust to the Mediterranean Sea, but dry deposition can also be important. The dust transport occurs in the form of “pulses”, and the annual dust flux can be controlled by a few episodes of Saharan outbreaks, e.g. sometimes a single outbreak can account for 40–80% of the flux. Saharan dust deposition fluxes range from 2 to 25 g m−2 (average ≅10) in the west Mediterranean between 39° and 42°N, from 6 to 46 g m−2 (average ≅20) in the east Mediterranean, and from 0.4 to 1.0 g m−2 over the Alps on continental Europe. The present day Saharan dust fluxes (≈ 1 mg cm−2 year−1) account for about 10–20% of the recent deep-sea sedimentation in the western Mediterranean (3–15 mg cm−2 year−1).

Trace elements in the oceans

Trace elements are present in sea water at concentrations that range down to picomoles per litre (pmol 1-1) and even lower. Such small concentrations pose extreme analytical problems, and it is only recently that these have been fully overcome. It is now known, for example, that contamination and the lack of sufficiently precise analytical techniques have led to reported concentration data that for some trace elements were too high by factors as much as 103. Because of this, real trends in the trace element data were sometimes totally masked by noise in the system, creating what Chester (1985) described as a ‘frustration barrier’, which prevented marine chemists from being able to relate trace metal distribution patterns to a consistent oceanographic framework. However, in a keynote review, Bruland (1983) pointed out that the mid-1970s had seen a quantum leap in our knowledge of the oceanic distributions of trace elements. This leap had become possible as a result of major improvements in both analytical and collection techniques, especially with regard to the elimination of sample contamination, which allowed the noise to be filtered out of the data. A selection of the new trace element concentration data in sea water is given in Table 11.1. At the same time that trace element concentration data were being refined, there were also advances in our understanding of the speciation of the elements in sea water.

Eolian dust along the eastern margins of the Atlantic Ocean

Eolian dust has been collected from the marine atmosphere of the major wind systems along the eastern margins of the Atlantic Ocean between c. 27°N and c. 34°S. The dust-loadings decreased in the order; northeast trades (average 57 μg m−3 of air) > variable winds of the Intertropical Convergence Zone (average, 0.23 μg m−3 of air) > southeast trades (average, 1.14 μg m−3 of air) > South Atlantic southerly winds (average, 0.07 μg m−3 of air). The dust-loadings reflect the soil characteristics and local meteorological conditions of the adjacent land masses, and it is shown that the Sahara Desert in West Africa has a much greater effect on the dust content of the northeast trades, than the Namib Desert of Southwest Africa has on the dust content of the southeast trades. The < 2 μm clay mineralogy of the dusts has been compared to those of source-area soils and deep-sea sediments. Several important trends have been established: chlorite has only a small variation with latitude; illite decreases towards low latitudes; kaolinite increases in equatorial areas; no specific trends are apparent in the distribution of montmorillonite. The distribution of chlorite, illite and kaolinite in the dusts is similar to that in deep-sea sediments, and reflects the soil clay mineralogy of the adjacent land areas. Eolian dust falling out from the northeast trades can make a significant contribution to the land-derived suspended material in the upper layers of the underlying sea water. However, fallout from the major winds in the South Atlantic Ocean makes up ⪡ 1% of the total land-derived material in the underlying waters.

Saharan dust incursion over the tyrrhenian sea

Abstract The Tyrrhenian Sea aerosol was sampled by both mesh and filter techniques. Geostrophic back trajectories were used to identify potential aerosol catchment regions, and it was shown that the atmosphere over the Tyrrhenian Sea received incursions of Saharan dust during the collection period in the autumn of 1979. Mineralogical and chemical parameters were used to characterize this desert-derived material and it was shown that it exerts an important influence on the composition of the local aerosol. On the basis of the present data, it was concluded that the northward movement of Saharan dust across, the Mediterranean can result in the transport of relatively large amounts of crustal material to the southern European coast and so should be included in estimates of Saharan dust production.

Dry atmospheric inputs of trace metals at the Mediterranean coast of Israel (SE Mediterranean) : sources and fluxes

Abstract This study presents the first detailed data on aerosol concentrations of trace metals (Cd, Pb, Cu, Zn, Cr, Mn, Fe and Al) at the SE Mediterranean coast of Israel, and assesses their sources and fluxes. Aerosol samples were collected at two sampling stations (Tel-Shikmona and Maagan Michael) along the coast between 1994 and 1997. Two broad categories of aerosol trace metal sources were defined; anthropogenic (Cd, Cu, Pb and Zn) and naturally derived elements (Al, Fe, Mn and Cr). The extent of the anthropogenic contribution was estimated by the degree of enrichment of these elements compared to the average crustal composition (EFcrust). High values (median >100) were calculated for Cd, Pb and Zn, minor values for Cu and relatively low values (

Soil-sized eolian dusts from the lower troposphere of the eastern Mediterranean Sea

Soil-sized eolian dusts have been collected by a mesh technique from the lower troposphere of the eastern Mediterranean. The overall average dust-loading in this region is 14 μg m−3 of air, which is among the highest recorded for maritime soil-sized dusts. There are two distinct dust populations in the eastern Mediterranean; these have been termed the “northeastern Mediterranean assemblage” and the “southeastern Mediterranean assemblage”. The dusts of the “northeastern assemblage” originate in the soils of southern Europe. The average dust-loading of this assemblage is 12 μg m−3 of air, and illite is the principal clay mineral with secondary amounts of kaolinite and the smectites. These dusts make only a secondary contribution to the land-derived material in the underlying deep-sea sediments. The dusts of the “southeastern assemblage” have their origin in the desert belts of North Africa and the Middle East. Their average dust-loading is 17 μg m−3 of air, and kaolinite is their dominant clay mineral. Dusts of the “southeastern assemblage” make an important contribution to the land-derived fractions of some eastern Mediterranean deep-sea sediments. In addition to eolian dusts, river-transported material from the island of Cyprus has also been investigated. The effects of this “Cyprus assemblage” on sedimentation in the eastern Mediterranean is confined to the immediate vicinity of the island itself.

The characterisation of Saharan dusts and Nile particulate matter in surface sediments from the Levantine basin using Sr isotopes

Abstract The provenance of sediments within the Levantine basin of the eastern Mediterranean was studied using 87 Sr/ 86 Sr isotopic ratios, together with major elements. Measurements were made on the detrital fraction of surface sediments, and the two most important sources of detrital matter to the region. Saharan dust was characterised by an 87 Sr/ 86 Sr isotopic ratio in the range 0.7160–0.7192. There was a small systematic decrease in 87 Sr/ 86 Sr from west to east which is interpreted as due to a change in the balance of aeolian source material. The Nile particulate matter had a 87 Sr/ 86 Sr isotopic ratio in the range 0.7057–0.7071. 87 Sr/ 86 Sr isotopic signatures together with Sr concentration were used to calculate the contributions made by Saharan dust and Nile particulate matter to the surface sediments of the Levantine basin. It was shown that Nile-derived sediment was dispersed widely across the Levantine basin enabling the area affected by retention of sediment behind the Aswan dam to be determined.