The geochemistry of Sepetiba Bay was studied in four sediment cores using a multi-element approach. Two cores were sampled in the more contaminated eastern part of the bay and two cores were sampled in the western region. The aim was to determine whether less common elements like the rare earths or the actinides are associated with contaminant metals like zinc in the Bay. Samples were analysed by instrumental neutron activation analysis that permits the quantification of total concentrations of metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), rare earth elements (Ce, Eu, La, Lu, Sm and Yb), actinides (Th, U), non-metals and semi-metals (As, Br). Organic carbon and total sulphur were also analysed. The results show very strong zinc contamination in the top layers (more than 1000 μg g−1) and background concentrations in the bottom (15 μg g−1). Elements like chromium which would be expected to be released by the heavy industries of Sepetiba Bay, did not show a contamination profile, and concentrations remained close to those of natural environments. No evidence of any association between the zinc and other potential contaminant elements could be identified in this work. 相似文献
The seismic analysis of the sedimentary infill of the Ría de Vigo reveals that the infill comprises of a fifth order sequence (18 ky) bounded by a major discontinuity surface. Within the Holocene sequence, several seismic units have been identified; the oldest one originated after the Würm glaciation and the origin of its top discontinuity was eroded during the regression (sea level at − 120 m) of this last glacial episode (isotopic stages 2 to 4), 18 ky B.P.
In some places below this ría infill, another sequence can be identified. This older sequence is associated with the pre-existing faults and troughs in the deepest parts of the ría, and it was deposited during the Würm glaciation (Miocene–Pleistocene). Eroded sediments were moved from the rías area to deeper zones, where they accumulated in the lowstand system tract. The next sea level rise occured in two steps, producing two transgressive units separated by an hiatus surface. This cycle was interrupted by the next sea level fall (to − 55 m) marked on the seismic records by another recognizable boundary. The next sea level rise took place in several steps (back-stepping) with some stillstands, generating another transgressive system tract in the ría. From that time on, the relative sea level continued rising, depositing the most recent unit which represents the highstand system tract. Separating the highstand system tract and the transgresive unit below there is a consensed section.
The analysis of 29 cores provides groundtruthing for our hypothesis. The identified main lithologic units show a transgressive sequence: a granitic rock base, an overlying second unit-locally wedge shaped- and most recently, a marine muddy unit covering the present ría seafloor. 相似文献
Electrochemical methods based on adsorption of organic molecules at the mercury electrode-solution interface were used to investigate surfactant production by marine phytoplankton. Six species of marine phytoplankton, representing the classes of Bacillariophyceae, Haeptophyceae, Chlorophyceae and Cryptophyceae, were studied in batch cultures.Our experimental results showed that surfactants were produced in culture media by healthy exponential growing cells. The measured response was found to depend on the particular species and the age of the culture.Total surfactant content in culture media generally increased with cell density, while surfactants per cell showed an inverse relation to cell density. However, we found that in Cryptomonas culture medium, during the exponential growth, excretion of the insoluble surfactant material per cell was independent of cell concentration.In addition to culture experiments, surfactant activity at several northern Adriatic stations was measured during various stages of phytoplankton bloom. It was concluded that a significant part of surfactant activity in a seawater column is due to phytoplankton production. 相似文献
The macrobenthic community structure and characteristics of sediments were studied in samples collected seasonally at five stations in the lower mesotidal Douro estuary, Portugal. Sediment characterisation included grain size distribution, total-recoverable metals (Al, Fe, Mn, Zn, Cu, Cr, Pb, Ni and Cd), acid-volatile sulphides (AVS) and simultaneously extracted metals (SEM) and total organic matter contents. Spatial variation surpassed temporal variation both in terms of environmental parameters and community structure. Clear anthropogenic contamination in terms of Zn, Cr, Cu and Pb, and a positive SEM-AVS, indicating the potential bioavailability of these metals, were detected on the north bank of the estuary. Multivariate analysis revealed that in addition to natural sediment characteristics, the anthropogenic metal contamination was influencing the macrobenthic community structure. In fact, greater concentrations of Zn, Cr, Cu and Pb were associated with lower number of species and/or diversity. Finally, the dry weight-normalised metal concentrations appeared as a more useful tool than the SEM-AVS model in predicting disturbance of the macrobenthic community in the studied area. 相似文献
The need for quantifying and understanding the distribution of shallow gas is both of academic interest and of relevance to
offshore facilities. The combination of seafloor mapping, subbottom profiling, and multi-channel seismic data can provide
information on regions of possible shallow gas, where the gas impacts the acoustic properties of the host material and the
seafloor. In this paper, we present two case studies – one academic and one industry – that evaluate the distribution of shallow
gas in two field areas in the Mediterranean. In the first case study, geophysical data from Iskenderun Bay, southeastern Turkey,
indicate the presence and distribution of shallow gas. Pockmarks on the seafloor are associated with acoustic wipeout in the
shallow subbottom data. Although deeper seismic data do not show bright spots or other indicators of possible gas, instantaneous
frequency analysis clearly shows laterally restricted anomalies indicating gas-rich zones. The interpretation of possible
shallow gas resulted in moving a proposed drilling location to a nearby area characterized by fewer (but still present) shallow
gas signatures. In the second case study, cores acquired in the Po Delta, Adriatic Sea, provide quantitative ground-truthing
of shallow gas – as suggested by geophysical data – and provide minimum estimates of the percentage of gas in the subsurface.
Cores targeted on anomalous subbottom data yielded up to 41,000 ppm methane; cores with anomalous gas content are associated
with thick recent flood deposits which may effectively isolate reactive terrigenous organic matter from biologic and physical
re-working. 相似文献