Organochlorinated compounds in Caspian Sea sediments

Several organochlorinated contaminants, including numerous pesticides, were determined in coastal sediments from the Caspian Sea. The most important contaminants were p,p'-DDT (up to 7400 pg g(-1)) and its breakdown products, p,p'-DDD (up to 3400 pg g(-1)) and p,p'-DDE (up to 1300 pg g(-1)). Although the contamination was most severe in Azerbaijan, the sediment concentrations and percentage distribution of the three DDT-related compounds indicated that such contamination constitutes a contemporary and ubiquitous problem in the Caspian Sea. Lindane represented the second most significant contaminant, particularly in the Russian Federation, with concentrations up to 609 pg g(-1). The concentrations of HCB and other chlorinated pesticides (cis- and trans-chlordane, methoxychlor, heptachlor, heptachlor epoxide, aldrin, endrin, and endosulfans) were lower and not generally of concern, but the pesticides did demonstrate markedly different distributions reflecting differing agricultural usage in the region. The concentrations of Sigma PCBs were also quite low and ranged from 0.03 to 6.4 ng g(-1), with the highest amounts in the Russian Federation and Azerbaijan.     

Evolution diagénétique dans la craie pélagique dolomitisée du crétacé supérieur du bassin de Paris (région de Provins, France)

Two deep scientific boreholes, named Poigny 701 and Sainte-Colombe 702, located in the Paris Basin near Provins (Seine-et-Marne, France), recovered a complete Upper Cretaceous chalk succession. A correlation between the boreholes lithostratigraphy, reflexion seismic profiles and diagenetic patterns shows that major velocity variations measured in the seismic reflection profiles correspond to dolomitized chalk intervals. Dolomitisations occurred during early and burial diagenesis. The understanding of these complex diagenetic events has an important economic consequence on the static correction of the chalk formation in the Paris Basin. Optimisation of petroleum prospecting below chalk cover is thus possible. The chalk series of the 701 and 702 boreholes range from the Cenomanian to the upper Campanian. In this succession, micrite has a primarily biogenic origin; it consists of pelagic organisms, indicative of warm seawater with values around 25°C. Several hiatuses occur in the 701 borehole. These hiatuses indicate the existence of particular hydrodynamic conditions. Deep-water channels were locally recognised in the Paris Basin as in Normandy and Picardy. In the 702 borehole, massive dolomitisation affected the upper meters of sediment below the sea floor. This early phase of massive dolomitisation was induced by slow circulation of a magnesium-rich seawater mass, along the seawater/sediment interface. Thus, this area was a zone of intense marine circulation between the North-West infralittoral and the South-West bathyal domains, across the London-Paris Basin. Magnesium-rich seawater had as origin the recrystallisation of the biogenic peri-plateform carbonates. During both dolomitisation and dissolution of the calcite matrix of the massive dolomite, the calcite had cemented chalk around the massive dolomite body. After deposition, the chalk series was progressively compacted and lithified by burial calcite cement. During the late Campanian-Maastrichtian, the burial compaction of the chalk and thermal gradient reached their maximum, as compressive stresses from the Pyrenean orogenesis affected the Paris Basin. At this time, compaction of the massive dolomite induced the expulsion of magnesian-rich fluids into the underlying already compacted chalk series. In 702 borehole, a diffuse dolomitisation then affected strongly underlying the chalk series. In 701 borehole, this diffuse dolomitisation affected slightly the lower half of the chalk series. Laterally, dolomitisation decreases gradually and affected a only smaller thickness of the chalk series, disappearing laterally. During the progressive emergence of the Paris Basin, from the Paleogene to the Quaternary, the chalk series were partially invaded by continental fresh water. Thus partial dedolomitisation affected the massive dolomite, whereas total dedolomitisation affected only the upper first meters of it.Manuscrit reçu le 20 juin 2003 Révision acceptée le 9 septembre 2004     

Variability of the gas transfer velocity of CO<Subscript>2</Subscript> in a macrotidal estuary (the Scheldt)

We report a large set of 295 interfacial carbon dioxide (CO₂) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant measurements of the air-water CO₂ gradient, we computed the gas transfer velocity of CO₂. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to the gas transfer velocity, using the conceptual relationship of O'Connor and Dobbins (1958). This allowed us to construct an empirical relationship to compute the gas transfer velocity of CO₂ that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability of the gas transfer velocity in the Scheldt estuary was investigated. Water currents contribute significantly to the gas transfer velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability.     

Modelling of scattering of seismic waves from a corrugated rough sea surface: a comparison of three methods

We compare three numerical methods to model the sea surface interaction in a marine seismic reflection experiment (the frequencies considered are in the band 10–100 Hz): the finite-difference method (FDM), the spectral element method (SEM) and the Kirchhoff method (KM). A plane wave is incident at angles of 0° and 30° with respect to the vertical on a rough Pierson–Moskowitz surface with 2 m significant wave height and the response is synthesized at 6, 10 and 50 m below the average height of the sea surface. All three methods display an excellent agreement for the main reflected arrival. The FDM and SEM also agree very well all through the scattered coda. The KM shows some discrepancies, particularly in terms of amplitudes.     

Rhine flood deposits recorded in the Gallo-Roman site of Oedenburg (Haut-Rhin, France)

From the first to the fourth century AD, the Gallo-Roman town of Oedenburg developed in the alluvial landscape of the southern Upper Rhine Graben. Throughout this period, the landscape mosaic, composed of palaeochannels, stable palaeoislands and river terraces, continued to evolve. A district of this town, situated on a lateral Rhine channel system, was archaeologically excavated. Large-scale excavation and cross-section analysis provide evidence of changing fluvial conditions during the period under study. At about AD 20 or earlier, this lateral part of the floodplain, affected by very fine sedimentation, was occupied by moribund marshy palaeochannels. When the first Gallo-Roman settlers occupied the site, they filled parts of the channels with woven brushwood in order to create an efficient circulation surface. The sedimentary infill of this palaeochannel records four different flood deposits interlayered with dated anthropogenic units (pavements, road embankments, and other structures). Archaeological analysis and dendrochronological dating indicate that these four flooding events occurred during a short time period between AD 20 and AD 145/146. These geoarchaeological observations focus on floods that do not seem to have significantly affected human occupation in this part of the Rhine floodplain. These results are set in the broader context of the Rhine catchment and the Alps.     

Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)

Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the 1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m⁻² d⁻¹) decreasing seaward (22–37 mmol C m⁻² d⁻¹). A significant decrease of NIT was observed with regard to previous investigations although this process still represents up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time in the estuary with values ranging from −300 to 165 mmol C m⁻² d⁻¹. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published benthic metabolic rates. A NEP of −39±8 mmol C m⁻² d⁻¹ was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m⁻² d⁻¹) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.     

Late Cenozoic geodynamic evolution of eastern Indonesia

This paper presents an internally and globally consistent model of plate evolution in eastern Indonesia from Middle Miocene to Present time. It is centered on the Banda Sea region located in the triple junction area between the Pacific–Philippine, Australia and South–East Asia plates. The geological and geophysical data available from Indonesia were until recently insufficient to define a unique plate tectonic model. In this paper, the new data taken into account clearly restrict the possible interpretations. Owing to a great number of geological, geophysical and geochemical studies, the major plate boundaries (the Sunda–Banda subduction zone to the south, the Tarera–Aiduna Fault zone and the Seram Thrust to the east, and the Sorong Fault zone and Molucca Sea collision zone to the north) are now clearly identified. The age of the major tectonic structures is also better known. Geodetic measurements well constrain the Present time plate kinematics. We also consider the deformation history within eastern Indonesia, where numerous short-lived microplates and their related microcontinents successively accreted to the Asiatic margin. Moreover, magnetic anomalies identification of the North and South Banda Sea basins allows a precise kinematic reconstruction of the back-arc opening. We used the Plates software to test the coherency of our model, presented as a series of 4 plate reconstruction maps from 13 Ma to the present. Finally, the origin of oceanic domains restored by our reconstruction is discussed.