New Development of Eastern Mediterranean Circulation based on Hydrological Observations and Current Measurements

Abstract. A number of recent studies based on hydrographic observations and modelling simulations have dealt with the major climatic shift that occurred in the deep circulation of the Eastern Mediterranean. This work presents hydrographic observations and current measurements conducted from 1997 to 1999, which reveal strong modifications in the dynamics of the upper, intermediate and deep layers, as well as an evolution of the thermohaline characteristics of the deep Aegean outflow since 1995. The reversal of the circulation in the upper layer of the north/central Ionian is worthy of note. The observations indicate a reduction of Atlantic Water in the northern Ionian with an increase on the eastern side of the basin. In the intermediate layer, the dispersal path of the Levantine Intermediate Water (LIW) is altered. Highly saline (>39.0) and well-oxygenated intermediate waters were found near the Western Cretan Arc Straits. They flow out from the Aegean, thus interrupting the traditional path of the LIW, and spread prevalently northwards into the Adriatic Sea. In the deep layer, dense waters, exiting from the Adriatic (σ_ø−29.18 kg · m⁻³), flow against the western continental margin in the Ionian Sea at a depth of between 1000–1500 m. Dense waters of Aegean origin (> 29.20 kg · m⁻³), discharged into the central region of the Eastern Mediterranean during the early stages of the transient, propagate prevalently to the east in the Levantine basin and to the west in the northern Ionian Sea. Near-bottom current measurements conducted in the Ionian Sea reveal unforeseen aspects of deep dynamics, suggesting a new configuration of the internal thermohaline conveyor belt of the Eastern Mediterranean.     

The measurement of the gravitational constant in an orbiting laboratory

We propose to measure the gravitational constantG by putting in an orbiting laboratory a known mass of very high density and by tracking the motion of a small test mass under the gravitational influence of the primary mass. We analyse the different sources of perturbation; the consideration of the Earth's gravity gradient leads us to conclude that, if the laboratory is in a low Earth orbit, we cannot get stable satellite-like orbits of the test mass, but we must study only a process of gravitational scattering. In order to maximize the time of interaction it is proposed to use the practical stability of a collinear equilibrium point of the system Earth-primary mass, by putting the test mass as close as possible to the stable manifold of an equilibrium point. This method will allow the determination of the value ofG within a few parts over 10⁵, as shown by some computer simulations of the experiment taking into account also some unknown perturbation and random noise.Two main problems are involved in this experiment: (a) refined numerical methods are needed to take into account all significant perturbations and to extract the result aboutG from the experimental data; (b) during the motion of the test mass, the primary mass must always be free-falling inside the laboratory, so that this experiment needs a drag-free satellite technique of the same type which is necessary for high-precision gravimetric measurements.     

Geochemical features of rocks,stream sediments,and soils of the Fiume Grande Valley (Calabria,Italy)

The role of both natural weathering and anthropogenic pollution in controlling the distribution of major oxides and several trace elements in soils, stream sediments, and rocks of the Fiume Grande catchment was evaluated. The contents of major oxides and trace elements in soils appear to be governed by weathering and pedogenetic processes, although the use of fertilizers in agriculture could also partly affect K₂O and P₂O₅ contents. Stream sediments have concentrations of major oxides (except CaO) very similar to soils, as relevant amounts of soil materials are supplied to the stream channels by erosive phenomena. In contrast, stream sediments have concentrations of Cr, Co, Ni, Zn, As, and Pb significantly higher than those of soils, probably due to different conditions and rates of mobility of these elements within the three considered matrices and/or disposal of wastes in the drainage network. Comparison of the concentrations of PHEs in soils with the maximum admissible contents established by the Italian law shows that these limits are too restrictive in some cases and too permissive in other ones. The approach of setting these limits with no consideration for the local geological–geochemical framework may lead to improper management of the territory and its resources. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Flow Changes and Geochemical Anomalies in Warm and Cold Springs Associated with the 1992–1994 Seismic Sequence at Pollina,Central Sicily,Italy

During a three-year discontinuous geochemical monitoring of some warm springs and cold discharges located in central-northern Sicily, some hydro-geochemical changes were observed. Excluding a possible related to a moderate seismic activity were accidentally identified. The observed anomalies showed amplitudes that were modulated by the different geometries and volumes of the feeding aquifers. A poroelastic aquifer contraction, a shaking-induced dilatancy theory as well as seismogenetic-induced changes in the properties of the aquifers have been proposed as possible mechanisms for the water flow and hydro-geochemical changes. These preliminary results could be used to design a monitoring network aimed at surveilling the seismic activity of the studied area from a geochemical standpoint.     

Recent evolution of surge-related events and assessment of coastal flooding risk on the eastern coasts of the English Channel

This paper is based on statistical analysis of hourly tide measurements for some 285 equivalent full years from the stations of Weymouth, Bournemouth, Portsmouth, Newhaven, Dover and Sheerness in the UK, and of Cherbourg, Le Havre, Dieppe, Boulogne, Calais and Dunkirk in France. For each tidal value, surge heights have been determined and correlated with hourly or three-hourly wind and air pressure data from nearby meteorological stations. Major surges in the area are generally produced by storms associated with wind from north-west or south-west that tend to push oceanic water into the Channel. Recent medium-term climate evolution does not seem to increase the flooding risk at French stations, where surge-related winds tend to decrease in frequency and speed (Cherbourg, Dieppe and Boulogne) or show little change (Le Havre). However, the long-term risk of flooding will increase through the loss in land elevation due to a continuation of the local relative sea-level rise, especially if this effect will be enhanced by an acceleration in the global sea-level rise predicted by climatic models. The northern side of the Channel (Weymouth, Bournemouth and Portsmouth) is mainly exposed to southerly winds that show variable trends. It is also apparently affected by strong subsidence trends during the last two decades. If lasting, such trends can only increase long-term flooding risk. The flooding risk has not increased near the eastern end of the Channel. The duration of significant cyclonic events tends to decrease near Cherbourg but tends to increase near Weymouth, with no conclusive trends in other stations (Portsmouth, Calais and Dunkirk), where extreme surges may occur also in relatively high-air-pressure situations. In conclusion, medium-term coastal flooding risk seems to increase especially at Weymouth, Bournemouth and Portsmouth, and also, but less so, at Le Havre and Sheerness. In addition, few extreme surges occurred during the last decades at the time of spring high tide, which would seem to be a fortunate coincidence or, in some cases, an effect of tide–surge interaction. The risk of occurrence of less favourable random events in the near future is therefore of concern, and flood potential would greatly increase if the global sea-level rise expected in the near future is also considered.     

Mantle–crust interactions during Variscan subduction in the Eastern Alps (Nonsberg–Ulten zone): geochronology and new petrological constraints

We have analyzed the Sm–Nd and Rb–Sr whole-rock and mineral isotope systematics of garnet peridotites and associated eclogites and migmatitic gneisses from the Nonsberg–Ulten zone of the Eastern Alps. The garnet peridotites include coarse-grained varieties, characterized by well-preserved to slightly modified mantle geochemical signatures, and finer-grained varieties enriched in amphibole and LILE. Hydration of some of the most strongly deformed, fine-grained peridotites by crustal fluids caused isotopic disequilibrium between the peridotite minerals, preventing accurate age determinations. The coarse-grained peridotites, the eclogites and the country migmatitic gneisses yield garnet–whole-rock and garnet–clinopyroxene Sm–Nd ages that indicate for all rock types an isotopic homogenization event at ca. 330 Ma. The similar ages suggest that all rock types shared a common history since the incorporation of the peridotites in the crust, and constrain the garnet-facies metamorphism of the peridotites, as well as partial melting of the crust, to an episode of crustal subduction at the end of the Variscan orogenic cycle.     

An integrated geophysical investigation of the upper crust in the epicentral area of the 1980, Ms=6.9, Irpinia earthquake (Southern Italy)

In this paper, we investigate the upper crustal structure of the Irpinia region, Southern Apennines thrust belt, Italy, through analysis and joint interpretation of gravity data, seismic reflection lines and subsurface information from many deep wells. The investigated region includes the epicentral area of the 1980 (M_s=6.9) Irpinia earthquake and is one of the Italian regions with the highest seismic hazard. The upper crustal structure is imaged by modeling a series of 15 SW-trending gravity profiles, spaced about 5 km apart, plentifully constrained by seismic reflection lines and wells, thus reducing the inherent ambiguity of the gravity modeling. Despite of the complexity of the modeled Bouguer anomalies, the application of a calibrating procedure to constrain the range of variability of the density values, as well as the use of geometric constraints, results in a good level of stability in the final density cross-sections, which in fact appear coherent both in the density values and in the geometrical features. The inferred model shows important lateral density variations that can be mostly related to NW-trending geologic structures. High-density bodies delineate carbonate platform thrust sheets and broad antiforms involving Mesozoic basinal rocks, while low-density shallow bodies are associated with Pliocene basins. In addition, important density (i.e. lithological) variations are evident along the strike of the range, the most relevant being an abrupt deepening of the Apulia Carbonate Platform in the southeastern part of the investigated region. In the epicentral region of the 1980 event, we find that the geometry of the high-density, high-velocity carbonates of the Apulia Platform appears correlated with the distribution of the aftershocks and with the P-wave velocity anomaly pattern as inferred from a previous local earthquake tomography. The structural highs of the Apulia Platform correspond to high-velocity regions, where aftershocks and coseismic slip of the mainshock are concentrated. This correlation suggests that the Apulia Carbonate Platform geometry played an important role in the rupture propagation and in the aftershock distribution.