Hydrology, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea), during September 2001–October 2001 and February 2002

The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea) are described, for September 2001 and October 2001 and February 2002. The observations were obtained to assess the impact of anthropogenic and natural resuspension processes on the coastal ecosystem. The first two periods represent highly stratified conditions and mild weather conditions; in September trawling is prohibited, whilst the October cruise took place following the commencement of the activity. The sampling in February was undertaken to record the contribution of natural resuspension to the system, in a stormy period.The water circulation was mainly baroclinic during autumn and barotropic in winter; this was due to vertical homogenisation of the water column, during the latter period. The distribution of the bottom nepheloid layer (BNL) was very different in the winter than in the autumn.Microstructure measurements were undertaken, which allowed the vertical eddy diffusivity to be estimated, together with the near-bed shear stresses. Computation of the diffusive flux of particulate matter (PM), from the BNL into the intermediate water column in response to turbulent motions, reveals that the PM flux was much higher in October than in September; this is despite the fact that the friction velocities were similar. This observation could explain partly the observed higher PM concentrations (PMC) in the intermediate layer, in October. Likewise suggest that the higher PMC in October could be attributed to trawling. The limited shear stress and friction velocity values obtained during the September and October cruises were always low; these were possibly capable of resuspending only recently deposited, “fluffy” material. Thus, the observed nepheloid layers are likely to be maintained by advection from the shallow water regions and trawled areas.     

Sliding element simulating the response of slip surfaces and its application for the prediction of earthquake-induced landslide movement using one-dimensional dynamic analyses

Landslides - Earthquake-induced landslides involve excessive movement of slopes, usually along slip surfaces. This seismic movement of slopes may depend crucially on (a) the soil response along the...     

New radiolarian biostratigraphic age constraints on Middle Triassic basalts and radiolarites from the Inner Hellenides (Northern Pindos and Othris Mountains, Northern Greece) and their implications for the geodynamic evolution of the early Mesozoic Neotethys

The Avdella Mélange in the northern Pindos Mountains and its equivalent formation, the Loggitsion Unit in the Othris Mountains expose early Mesozoic (Mid-Late Triassic) oceanic fragments beneath the Western Greek Ophiolite Belt of the Inner Hellenides, Northern Greece. The mélange consists of locally interfingering blocks and slices of ribbon radiolarite, radiolarian chert and pillow basalt and is usually overthrust by Jurassic ophiolites. New Middle and Upper Triassic radiolarian biostratigraphic data are presented from radiolarites and basalt-radiolarite sequences within mélange blocks. Pillow basalts associated with the radiolarites provide clues to the opening of the Neotethyan ocean basin. The radiolarians indicate a Middle Triassic age (latest Anisian, probably early Illyrian), which is documented for the first time in the northern Pindos Mountains. The new radiolarian biostratigraphic data suggest that rift-type basalt volcanism already began in pre-Ladinian time (late Scythian?—Anisian). These basalts were then overlain by Upper Anisian to Carnian (?Norian) radiolarites.     

Suspended particulate matter and nepheloid layers over the southern margin of the Cretan Sea (N.E. Mediterranean): seasonal distribution and dynamics

Seawater along the southern margin of the Cretan Sea (May 1994–September 1995) has been found to have light transmission values ranging from 79% to 94%, corresponding to SPM values ranging from 1.5 mg l⁻¹ to 0.2 mg l⁻¹. The highest SPM concentrations (mostly of terrigenous origin) were found close to the sea-bed over the shelf-break and upper slope. The origins of SPM in the surface waters (<150 m) is principally biogenic. The occurrence of nepheloid layers at intermediate depths within the upper water column is mostly a result of density stratification. The dynamics of SPM distributions are governed by the 2-gyre system which induces a general onslope flow; and so inhibits the seaward dispersion of the relatively more turbid coastal/shelf waters. This is in agreement with the virtual absence of suspensates of terrigenous origin offshore of the shelf-break. Near bottom nepheloid layers (BNL) and detached intermediate nepheloid layers occur in the vicinity of the shelf-break and over upper slope region; these may be explained by resuspension induced by near-bed current activity and breaking of internal waves. High concentrations of SPM near the seabed may be caused by anthropogenic (trawling) activity. Occasionally, the formation of BNL may result from local seismic activity resulting in gravity-driven mass movements.     

Microseismicity and faulting geometry in the Gulf of Corinth (Greece)

During the summer of 1993, a network of seismological stations was installed over a period of 7 weeks around the eastern Gulf of Corinth where a sequence of strong earthquakes occurred during 1981. Seismicity lies between the Alepohori fault dipping north and the Kaparelli fault dipping south and is related to both of these antithetic faults. Focal mechanisms show normal faulting with the active fault plane dipping at about 45° for both faults. The aftershocks of the 1981 earthquake sequence recorded by King et al . (1985 ) were processed again and show similar results. In contrast, the observations collected near the western end of the Gulf of Corinth during an experiment conducted in 1991 ( Rigo et al . 1996 ), and during the aftershock studies of the 1992 Galaxidi and the 1995 Aigion earthquakes ( Hatzfeld et al . 1996 ; Bernard et al . 1997 ) show seismicity dipping at a very low angle (about 15°) northwards and normal faulting mechanisms with the active fault plane dipping northwards at about 30°. We suggest that the 8–12 km deep seismicity in the west is probably related to the seismic–aseismic transition and not to a possible almost horizontal active fault dipping north as previously proposed. The difference in the seismicity and focal mechanisms between east and west of the Gulf could be related to the difference in the recent extension rate between the western Gulf of Corinth and the eastern Gulf of Corinth, which rotated the faults dipping originally at 45° (as in the east of the Gulf) to 30° (as in the west of the Gulf).     

Comments on “Cascades of dense water around the world ocean”

Evidences of temperature-controlled dense water cascading off the Gulf of Lion shelf, in the northwestern Mediterranean, and several Aegean shelves in the northeastern Mediterranean are reported. Together with the Adiatic shelf, already listed by Ivanov, Shapiro, Huthnance, Aleynik, & Golovin (2004), these zones represent the major coastal areas of the Mediterranean Sea where dense water is produced.     

Brittle-Ductile Transition and Hoek–Brown mi Constant of Low-Porosity Carbonate Rocks

Geotechnical and Geological Engineering - The mechanical behavior of low porosity carbonate rocks is investigated by a series of conventional triaxial compression tests performed at room...     

Monitoring the physical forcing of resuspension events in the Thermaikos Gulf—NW Aegean during 2001–2003

This work constitutes an attempt to assess the relative importance of natural versus anthropogenic forcing for sediment resuspension on the shelf of the Thermaikos Gulf (NW Aegean) through a 2-year experiment in the framework of the E.U. project INTERPOL. Four periods of different hydrographic characteristics were identified, including two periods of stronger vertical homogenisation and two of stratified conditions. The former periods were characterized by stronger near-bed currents, while relatively weak internal wave motions dominated the periods of stratification. The near-bed currents showed strong coherence with the wind during the period of full homogenisation, whereas during stratification periods the wind provided indirect forcing evident mostly in the internal-wave bands. The site was too deep for the surface waves to cause any sediment resuspension. In conclusion, the observed near-bed currents at the site of interest did not appear to produce significant local resuspension of sediment; notably, the current-turbidity correlation suggested a shoreward transport of suspended material. The large-scale turbidity variability was rather related to the onset of the trawling period in mid-October 2001 and the increased riverine discharge in late summer/autumn 2002.     

First evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) from the Ionian Zone,western continental Greece

Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes) and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate—black shale succession of the Ionian Zone (western Greece), provide the first evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich (44.5 wt% TOC), carbonate-free black shale, near the Cenomanian–Turonian boundary within the Vigla limestone formation (Berriasian–Turonian). Compared to the ‘Bonarelli’ black-shale interval from the type locality of OAE2 in Marche–Umbria, Italy, this black shale exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched δ¹³C values for both bulk organic matter (−22.2‰) and specific organic compounds are up to 5‰ higher than those of underlying organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian–Turonian black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N₂-fixing cyanobacteria in Cretaceous oceans during the Cenomanian–Turonian and early Aptian oceanic anoxic events.