1,721,068 research outputs found
Impact of Natural and Trawling Events on Resuspension, dispersion and fate of POLlutants (INTERPOL). Introduction (to Special Issue)
No full textSedimentary environments in the northwestern Aegean Sea, identified from sea bed photography
No full textModern sedimentation in the N.W. Aegean Sea
No full textThe area under investigation is located within 22°45? to 23°45?E, and from 39°15? to 40°15?N. Sedimentological, bathymetric and shallow geophysical data were collected from here during the View the MathML source cruise of R.R.S. “Shackleton”. Twenty-seven sea-bed (surface) samples were collected, using a Day grab, from different environments; these were analysed for grain-size distribution, carbonate content, and clay mineralogy.On the basis of the bathymetric and shallow geophysical data, the area has been classified into five major physiographic environments, according to their bathymetry and topography: (1) shelf (Thermaicon Plateau); (2) slope; (3) marginal plateau; (4) the “canyon system” and valleys; and (5) (Sporades) basin.Based on the sedimentological analyses, the surface sediments have been classified into four major Provinces, as follows: (1) Province 1 — shelf muds; (2) Province 2 — muddy sands; (3) Province 3 — outer margin muds; and (4) Province 4 — outer shelf/shelf break.It is concluded that modern sedimentation in the N.W. Aegean Sea is dominated by the (terrigenous) river inputs and by the circulation of both high and low salinity masses
Temporal variations in sedimentation patterns: NW Aegean Sea
No full textCores are examined from the northern continental slope environment of the Sporadhes Basin, the western part of the North Aegean Sea Trough. Three distinct lithofacies have been identified, which correspond with similar environments identified elsewhere in the western and southeastern Mediterranean. These layers, turbiditic mud — hemipelagic mud ? calcareous ooze, represent late Quaternary climatic and eustatic sea level changes and tectonic activity.Based on benthic foraminiferal evidence from the eastern part of the North Aegean Sea Trough, it is suggested that contemporary sediment supply and physical oceanographic conditions in the area under investigation might be conducive to sapropel formation; also, that the depositional sequence in the cores represents a gradual recovery in the Mediterranean Sea, since its last stagnation and sapropel formation some 8000 years ago
Late Quaternary Evolution of Amvrakikos Gulf, Western Greece
No full textAmvrakikos Gulf is a Neogene basin, formed during a late extensional tectonic phase within the Plio-Quaternary period. It is a semienclosed embayment, separated from the Ionian Sea by a shallow (< 10="" m) channel. The analysis of 3.5-khz seismic reflection profiles shows that, during the last (würm) glacial period, the parts of the gulf that lie at water depths >41 m (below present sea level) were a paleo-lake while the rest were exposed to subaerial erosion. Subsequent offshore depositional sequences accumulated at rates of 1.2–2.
Thermaikos Gulf coastal system, NW Aegean Sea: an overview of water sediment fluxes in relation to air-land-ocean interactions and human activities
No full textThis study presents an overview of the Holocene formation and evolution of the coastal system of Thermaikos Gulf (NW Aegean Sea). The system is divided into the terrestrial sub-system and the oceanic sub-system; the former represents 90%, while the latter includes only 10% of the total area. This particular coastal zone includes the second most important socio-economic area of Greece and in the southern Balkans, the Thessaloniki region; this is in terms of population concentration (>1 million people), industry, agriculture, aquaculture, trade and services. The geomorphology of the coastal zone is controlled by sediment inputs, nearshore water circulation, and the level of wave activity. The large quantities of sediments (with yields >500 tonnes/km2 per year), delivered annually by the main rivers (Axios, Aliakmon, Pinios, and Gallikos) and other seasonal streams are responsible for the general progradation of the coastline and the formation of the Holocene sedimentary cover over the seabed of the Gulf. Changes to the coastline can be identified on macro- and meso-time scales; the former include the evolution of the deltaic plains (at >1 km2/year), while the latter incorporates seasonal changes along sections of the coastline (e.g. sandy spits), mostly due to the anthropogenic activities. The overall water circulation pattern in Thermaikos Gulf is characterised by northerly water movement, from the central and eastern part of the Gulf; this is compensated by southerly movement along its western part. The prevailing climate (winds and pressure systems) appears to control the surface water circulation, while near-bed current measurements reveal a general moderate (<15 cm/s) southerly flow, i.e. offshore, towards the deep water Sporades Basin. Waves approaching from southerly directions play also a role in controlling the shoreline configuration. Various human activities within the coastal system place considerable pressure on the natural evolution of the coastal zone ecosystem. Thus, the construction of dams along the routes of the main rivers has reduced dramatically the water/sediment fluxes; this caused, for example, retreat of the deltaic coastlines and seawater intrusion into the groundwater aquifers. Similarly, pollution and/or eutrophication of the nearshore marine environment have resulted from the inputs of industrial wastes, urban untreated sewage, and agricultural activities on the coastal plains. This effect is demonstrated by high levels of pollutants, nutrients, and by the increased concentrations of non-residual trace-metals within the surficial sediments. Finally, climatic changes associated with a potential rise in sea level (i.e. 30–50 cm) will threaten a substantial part of the low-lying lands of Thermaikos Gulf. Thus, systematic and thorough monitoring is needed in order to protect the coastal ecosystem; this will ensure its sustainable development and successful management, in relation to present and future socio-economic activities and climatic changes
Sedimentation processes in a tectonically active environment: the Kerkyra-Kefalonia submarine valley system (NE Ionian Sea)
No full textThe Kerkyra–Kefalonia valley system is the northwestern extension of the Hellenic arc–trench system, representing the collision zone of the Apulian Platform and the Hellenides. The system is distinguished by two different physiographic regions: the northern part, U-shaped, and oriented NNW–SSE, with relatively gentle slopes and a wide floor; and the southern part, oriented NE–SW, V-shaped, and with much steeper side walls and a narrow floor. Both parts are formed tectonically, with the former coinciding with a collision zone, and the latter being the morphometric expression of the Kefalonia strike–slip fault. Sediments recovered in the piston cores from the region consist of fine-grained material, deposited by a variety of sedimentation processes such as: gravity-driven mass movements, associated with seismic activity (i.e., slumping, sliding, debris flows, grain flows, turbidites–seismoturbidites); and, to a lesser extent, by hemipelagic deposition. Measured near-bed currents and their associated shear stresses indicate resuspension of the material, mainly within the northern part of the valley. Sub-bottom acoustic (seismic) profiling data reveal various sedimentary provinces, related to different mechanisms of sediment accumulation: (i) the eastern margin of the Apulian Platform with hemipelagic sedimentation, together with possible advection of suspensates from the Adriatic, in response localised to seabed erosion; (ii) the western Hellenic margin, with down-slope episodic sliding and slumping, induced primarily by earthquake activity, together with an input from hemipelagic settling; (iii) the collision zone, coinciding with the northern part of the Kerkyra–Kefalonia valley system, with deposition mostly from resuspension, the occurrence of local mass gravity flows and the advection of some material from the north; and (iv) the Kefalonia strike–slip fault region, where mass gravity flows are the dominant mechanisms, related to erosion/deposition from resuspension. Overall sedimentation within the tectonically-active Kerkyra–Kefalonia valley system is characterised by the coupling of the mass gravity-driven flows, which are the predominant mechanisms, with the near-bed current regime related with resuspension phenomena and the advection of suspensates. These latter mechanisms is likely more pronounced during the winter period, when dense water masses formed in the Adriatic inflowing into the Ionian Sea
Circulation changes and nutrient concentrations in the late Quaternary Aegean Sea: a nonsteady state concept for sapropel formation
Full text linkThe modern Aegean Sea is an important source of deep water for the eastern Mediterranean. Its contribution to deep water ventilation is known to fluctuate in response to climatic variation on a decadal timescale. This study uses marine micropalaeontological and stable isotope data to investigate longer-term variability during the late glacial and Holocene, in particular that associated with the deposition of the early Holocene dysoxic/anoxic sapropel S1. Concentrating on the onset of sapropel-forming conditions, we identify the start of “seasonal” stratification and highlight a lag in 18O response of the planktonic foraminifer N. pachyderma to termination T1b as identified in the 18O record of G. ruber. By use of a simple model we determine that this offset cannot be a function of bioturbation effects. The lag is of the order of 1 kyr and suggests that isolation of intermediate/deep water preceded the start of sapropel formation by up to 1.5 kyr. Using this discovery, we propose an explanation for the major unresolved problem in sapropel studies, namely, the source of nutrient supply required for export productivity to reach levels needed for sustained sapropel deposition. We suggest that nutrients had been accumulating in a stagnant basin for 1–1.5 kyr and that these accumulated resources were utilized during the deposition of S1. In addition, we provide a first quantitative estimate of the diffusive (1/e) mixing timescale for the eastern Mediterranean in its “stratified” sapropel mode, which is of the order of 450 years
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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