Mercury speciation in surface and deep waters of the Mediterranean Sea

Mercury speciation and its distribution in surface and deep waters of the Mediterranean Sea were studied during two oceanographic cruises on board the Italian research vessel URANIA in summer 2003 and spring 2004 as part of the Med Oceaneor and MERCYMS projects. The study included deep water profiles of dissolved gaseous Hg (DGM), reactive Hg (RHg), total Hg (THg), monomethyl Hg (MeHg) and dimethyl Hg (DMeHg) in open ocean waters. Average concentrations of measured Hg species were characterized by seasonal and spatial variations. Overall average THg concentrations ranged between 0.41 and 2.65 pM (1.32 ± 0.48 pM) and were comparable to those obtained in previous studies of the Mediterranean Sea. A significant fraction of Hg was present as “reactive” Hg (average 0.33 ± 0.32 pM). Dissolved gaseous Hg (DGM), which consists mainly of Hg⁰, represents a considerable proportion of THg (average 20%, 0.23 ± 0.11 pM). The portion of DGM typically increased towards the bottom, especially in areas with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea), indicating its geotectonic origin. No dimethyl Hg was found in surface waters down to the depth of 40 m. Below this depth, its average concentration was 2.67 ± 2.9 fM. Dissolved fractions of total Hg and MeHg were measured in filtered water samples and were 0.68 ± 0.43 pM and 0.29 ± 0.17 pM for THg and MeHg respectively. The fraction of Hg as MeHg was in average 43%, which is relatively high compared to other ocean environments. The concentrations reported in this study are among the lowest found in marine environments and the quality of analytical methods are of key importance. Speciation of Hg in sea water is of crucial importance as THg concentrations alone do not give adequate data for understanding Hg sources and cycling in marine environments. For example, photoinduced transformations are important for the presence of reactive and elemental mercury in the surface layers, biologically mediated reactions are important for the production/degradation of MeHg and DGM in the photic zones of the water column, and the data for DGM in deep sea indicate the natural sources of Hg in geotectonicaly active areas of the Mediterranean Sea.     

Reference sediment core and paleogeography of the underwater Slupsk river foredelta in the Baltic Sea

Core Psd-590 (length 947 cm, water depth 124 m) penetrated the entire sequence of marine (Littorina) mud (730 cm) and stopped in gray lacustrine (Ancylus) clays with hydrotroilitic films. The Littorina mud is gray-colored, microlaminated in the interval of 730 to 700 cm, and dark gray with hydrotoilitic films and obscure microlamination higher in the section. According to the diatom data, typical marine sediments begin at the level of 620 cm, while the lithological-geochemical data indicate this change at the level of 730 cm. This level is marked by a considerable increase in the concentrations of SiO_2amorph, CO₂, C_org, and Mn in the sediments. In the interval of 730 to 620 cm, diatoms are represented by both freshwater and brackish-water species. The Littorina transgression began in the form of individual flows of saline North Sea waters into the Baltic Sea, which is evident from the microlamination and sharp peaks in the concentrations of the chemical elements. The transgression exhibits two weakening and one strengthening (core interval of 380 to 220 cm) stages; the latter was marked by the maximal water salinity. The post-Littorina mud contains molluscan shells and fish bones and is enriched in the fraction of 0.05–0.01 mm. The microlaminated Littorina mud was deposited during periods with stagnant conditions in the bottom water layer, while the homogenous sediments accumulated during periods of its aeration.     

A detailed magnetic study of the Reykjanes Ridge between 63°00′N and 63°40′N

Immediately southwest of Iceland, the Reykjanes Ridge consists of a series ofen échelon, elongate ridges superposed on an elevated, smooth plateau. We have interpreted a detailed magnetic study of the portion of the Reykjanes Ridge between 63°00N and 63°40N on the Icelandic insular shelf. Because the seafloor is very shallow in our survey area (100–500 m), the surface magnetic survey is equivalent to a high-sensitivity, nearbottom experiment using a deep-towed magnetometer. We have performed two-dimensional inversions of the magnetic data along profiles perpendicular to the volcanic ridges. The inversions, which yield the magnetization distribution responsible for the observed magnetic field, allow us to locate the zones of most recent volcanism and to measure spreading rates accurately. We estimate the average half spreading rate over the last 0.72 m.y. to have been 10 mm/yr within the survey area. The two-dimensional inversions allow us also to measure polarity transition widths, which provide an indirect measure of the width of the zone of crustal accretion. We find a mean transition width on the order of 4.5±1.6 km. The observed range of transition widths (2 to 8.4 km) and their mean value are characteristic of slow-spreading centers, where the locus of crustal accretion may be prone to lateral shifts depending on the availability of magmatic sources. These results suggest that, despite the unique volcanotectonic setting of the Reykjanes Ridge, the scale at which crustal accretion occurs along it may be similar to that at which it occurs along other slow-spreading centers. The polarity transition width measurements suggest a zone of crustal accretion 4–9 km wide. This value is consistent with the observed width of volcanic systems of the Reykjanes Peninsula. The magnetization amplitudes inferred from our inversions are in general agreement with NRM intensity values of dredge samples measured by De Boer (1975) and ourselves. Our thermomagnetic measurements do not support the hypothesis that the low amplitude of magnetic anomalies near Iceland is the result of a high oxidation state of the basalts. We suggest that the observed reduction in magnetic anomaly amplitude toward Iceland may be the result of an increase in the size of pillows and other igneous units.     

Ocean bottom refraction seismograph (OBRS)

This paper describes a pop-up ocean bottom seismograph designed primarily for refraction surveys both on the continental shelf and in deep sea. Its development is the extension of our system based on seismic detectors located on the sea floor with radio transmission of seismic signals and used for seismic refraction studies on the continental shelf. The seismic detectors (vertical geophone or hydrophone and two orthogonally mounted horizontal geophones) are located outside of the pressure vessel on the main frame. Optionally, the seismic sensors may be decoupled from the main frame assembly. This decoupling is performed by a mobile arm positioning the separate three component sensor package on the sea floor.Contribution No. 455 of the Département Scientifique, Centre Océanologique de Bretagne.     

Quaternary evolution of the Gulf of İzmit (NW Turkey): a sedimentary basin under control of the North Anatolian Fault Zone

The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started to accumulate during a progradational phase, in a south-facing half-graben. A coarse-grained sedimentary unit prograding into the gulf from the south since 200 ka b.p. indicates a dramatic variation in the evolution of the gulf, with the initiation of a new strike-slip fault of the NAFZ and a corresponding uplift of the Armutlu Peninsula in the south of the gulf. During the evolution of this fault from a wide shear zone consisting of right-stepped strike-slip faults and pull-apart basins to a localized principal fault zone, sediments were deposited under the influence of northerly prograding terrestrial and shallow-marine conditions due to relative sea-level fluctuations in the Marmara Sea. During this period, the Gulf of İzmit was invaded mainly by Mediterranean and partly by Black Sea waters. In the latest glacial period, shallow areas in the gulf became subaerially exposed, whereas the central and western sub-basins of the gulf turned into lakes. The present evolution of the Gulf of İzmit is controlled by the after effects of the new rupture of the NAFZ and the estuarine nature of the gulf environment.     

Assessment of dissolved nutrients dispersal derived from offshore fish-farm using nitrogen stable isotope ratios (δ15N) in macroalgal bioassays

In this study, the dispersal of wastes from offshore fish farms was evaluated by analyzing nitrogen stable isotope ratios (δ¹⁵N) in macroalgae incubated in the water column at sites located at an increasing distance from the fish cages. Bioassays were performed at three fish farms situated in separate localities with different nutritional conditions (Canary Islands, Murcia and Catalonia) and varying in size, species of fish reared and annual production. Macroalgal bioassays were carried out in two different directions (DI and DII) and they were replicated at each distance in order to evaluate the effect of small-scale variability on the spatial extent of fish farm wastes. The results obtained with δ¹⁵N contribute to a better understanding of the application of nitrogen stable isotopes ratios in macroalgae as an effective bioindicator for tracing the dispersion of offshore fish farm wastes, and demonstrate that fish farm wastes can be traced even over distances of some km from the pollution source. In the Canary Islands, the maximum distance obtained for detection of fish farm wastes was between 450 and 700 m. Of the three installations studied, Murcia presented the greatest distance for detection of fish farm waste influence, ranging from between 1550 and 2450 m, whilst in Catalonia this distance was less than 120 m. In Catalonia, the results were masked by the influence of other sources of nitrogen, and thus fish farm wastes were detected at more reduced distances than expected. These results confirm that fish farm wastes can be traced using the nitrogen stable isotope ratios of macroalgae and that this method can also be useful for identifying areas of potential risk to some sensitive ecosystems, and as an early signal that changes in the community structure might occur.     

A new record of pasiphaeid shrimp of the genus <Emphasis Type="Italic">Pasiphaea</Emphasis> (Crustacea: Decapoda: Caridea) in Korean waters

A single specimen of the pelagic shrimps, Pasiphaea japonica Omori, 1976 (Pasiphaeidae) collected in the southeastern waters of Korea is described and illustrated. Although this species occurs widely in the Indo-West Pacific including the Japanese coast of the East/Japan Sea and the middle and southern parts of the East China Sea, this is the first record of the species and the genus in Korean waters. The species is distinguished from other congeners by the following combination of characteristics: non-carinate dorsal sixth abdominal somite with a terminal tooth, rudimentary pleurobranch on the eighth thoracic somite, merus of the first pereopod with more than eight spines, and almost entirely transparent white color.     

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Paléo-bactéries et minéralisations plombo-zincifères du Bled Zelfane (tunisie centrale)

Résumé Le Bled Zelfane est un synclinal mio-pliocène sur la bordure septentriono-orientale de l'ile de Kasserine. L'ile de Kasserine est une plate-forme devenue insulaire à partir du Crétacé supérieur et restée émergée jusqu'au Miocène moyen. Ce môle a été soumis apparemment pendant sa période continentale à un climat oxydant de type méditerranéen relativement sec. On note une certaine diversification dans la nature des dépôts en zones basses (secteur de Kasserine) et en zones hautes (secteur du Bled Zelfane). En zones basses, la sécheresse climatique a favorisé la formation de dépôts de gypse, d'argiles rouges et de calcrêtes. En zones hautes, une érosion par lessivage acide a créé des dépressions karstiques dans les calcaires du Crétacé supérieur (Aïn Khamouda) et dans les calcaires du Maëstrichtien (Sidi Mabrouk et Guémata). Le remplissage des cavités karstiques (poches, crevasses) s'est fait avec de l'argile blanche (halloysite), contenant des micro-cristaux de galène, avec de la calamine et des oxydes de fer. Les conditions climatiques étaient trop oxydantes pour que le zinc se dépose autrement que sous forme de calamine. Elles expliquent aussi la présence de paléo-algobactéries (aérobies) sur la calamine. La présence de micro-cristaux de galène dans l'halloysite serait liée à un sulfuretum et non à des conditions réductrices réelles. Il semble en effet que dans ces karsts du Bled Zelfane une flore bactérienne très riche a joué un rôle essentiel dans le piégeage d'éléments lourds et notamment dans la genèse de galènes supergènes et dans la cristallisation de la calamine. Une minéralisation, elle aussi plombo-zincifère, de type stratiforme, s'observe à la base de Miocène inférieur et montre de même des bactéries fossiles à foison.

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Bled Zelfane is a Mio-Pliocene syncline on the NE edge of the palaeo-island of Kasserine, a platform which became insular at the beginning of the Upper Cretaceous and remained emergent until the Middle Miocene. During its long emergence this platform was affected by an oxidising, relatively dry, Mediterranaean-type climate. There exists a certain diversity in the sedimentary accumulations in both the lower (Kasserine area) and upper (Bled Zelfane area) sectors of this palaeo-relief. In the lower sectors the dry climate has favourised gypsum, red clays and calcrete formation. In the higher sectors erosion and leaching by acid waters has created karstic depressions in the Upper Cretaceous (Aïn Khamouda) and in the limestones of Maestrichtian (Sidi Mabrouk and Guémata). The karst cavities (pockets and fissures) are filled with white, halloysite clays containing micro-crystals of galena associated with calamine (Zn) and iron oxides. The climatic conditions were too oxidising to permit the formation of Zn other than in the form of calamine. The dry climate is also an explanation for the presence of aerobic palaeo-algobacteria on this calamine. The presence of micro-crystals of galena within the halloysite is probably related to a sulfuretum and not to effective reducing conditions. It would seem that the presence of a rich bacterial flora within the karst at Bled Zelfane has played a significant role in the stabilisation of heavy elements, and especially the supergene genesis of the galena. A Lead/Zinc mineralisation also exists at the base of the Miocene. This latter is diffused through the cement in conglomerates and sandstones.