The Hellenic shelf lies within and around the Aegean microplate, which is one of the world's most... more The Hellenic shelf lies within and around the Aegean microplate, which is one of the world's most seismically active areas, and has experienced extreme tectonism throughout Quaternary time. This activity, together with eustatic sea-level changes and watercirculation patterns over the same time period, controls the overall configuration of the Hellenic shelf, the rates of uplift and subsidence, and determines the sediment supply and depot centre, as well as the sediment-transfer processes. The above-mentioned geological processes are the causative factors for the frequent occurrence of a variety of geological hazards, such as active faults, submarine gravitational mass movements, tsunami and active gas seeping from the seabed.
International Journal of Sediment Research, Mar 1, 2012
Acoustic classification systems and the Sediment Trend Analysis method were used to identify and ... more Acoustic classification systems and the Sediment Trend Analysis method were used to identify and map the bed diversity in a very shallow (<3.0m), coastal lagoon, Pappas lagoon, Western Greece. Analogue acoustic data, collected by means of a 100 kHz side scan sonar system, were digitized and classified into six acoustic classes using recently developed acoustic classification systems (SonarClass, TargAn). By comparing the acoustic classes to ground truth data consisting of sediment grain size and visual inspection of the lagoon-bed, it is demonstrated that the six acoustic classes correlate well with the predominant surface sediment types and vegetation. Thus the spatial distribution of the classes can be considered to represent the spatial pattern of the sedimentary assemblages of the lagoon. The grain size trend analysis identified three dominant sediment pathways and directional trends which could be related to the predominant wind direction, the sediment influx through the inlets and the sediment supply from a small stream in the southern part of the lagoon. The integration of acoustic and sedimentological data together with advanced data processing systems leads to a better understanding of the sedimentary, morphological and biological processes in a shallow lagoon in different spatial and temporal scales and will therefore be beneficial to both sedimentological and biotic-diversity studies.
Impacts of man-made acoustic noise on the marine environment are associated to the frequency and ... more Impacts of man-made acoustic noise on the marine environment are associated to the frequency and timing of any activity as well as the distribution and abundance of marine life. Offshore commercial operations, shipping activities, energy exploration and pile driving add noise to the already established ambient noise levels. Attention has been raised by the years to the topic of underwater noise and its effects on marine life, but the effects of underwater noise are not yet fully understood. As the adoption of the European Marine Directive (MSFD 2008/56/EC-Descriptor 11) has given great impulse to the research in this field, governments, companies and institutes are working to specify the background ambient noise levels. Those studies have formed the guidelines and have set the protocols for performing safer offshore operations, which are adopted by the major energy companies. Hellenic Petroleum S.A. has undertaken a Marine Seismic Survey in West Patraikos Gulf waters in Greece between January and February 2016, which was coupled with an intensive sound noise monitoring program. Acoustic data were collected around Marine Protected Areas of the Inner Ionian Archipelago during three monitoring phases: 1) the pre-start, 2) the concurrent and 3) the post-completion ones. Sound pressure levels (SPLs) were collected using drifting hydrophones deployed on a frequent schedule, spanning 1.5 months, collecting more than 130 hours of data. The ambient noise data gave insight into the footprints of the anthropogenic and biogenic factors on the soundscape of the Inner Ionian Archipelago. Most importantly, the recorded SPLs of the impulsive seismic and the continuous shipping noises were studied against the bearing and distance to the corresponding sound sources.
Our understanding of the distribution of coralligenous formations, throughout but mostly on the E... more Our understanding of the distribution of coralligenous formations, throughout but mostly on the Eastern Mediterranean seafloor, is still poor and mostly relies on presence-only opportunistic trawling and fishermen reports. Previous efforts to gather this information created relevant geodatabases that led to a first draft predictive spatial distribution of coralligenous formations in the Mediterranean Sea using habitat suitability modelling techniques. In the last few decades, the use of hydroacoustics to map the seafloor for various geotechnical and habitat mapping projects accumulated high amounts of detailed spatial information about these formations, which remains majorly unexploited. Repurposing these datasets towards mapping key habitats is a valuable stepping stone to implementing the EU Habitat Directive. In Greece, a unique volume of seafloor mapping data has been gathered by the Laboratory of Marine Geology and Physical Oceanography, Geology Department, University of Patras...
Straits are crossed by marine currents that are amplified due to constrictions. These nearshore h... more Straits are crossed by marine currents that are amplified due to constrictions. These nearshore high-velocity flows are problematic for offshore infrastructures (bridge pillars, cables, pipelines, etc), but constitute an interesting carbon-free energy source. Many modern straits are dominated by tidal currents which flow axially, with reversal directions and phase difference between the two interlinked basins. These tidal currents interplay with: sediment sources (including in situ carbonate production and deltas), tectonic activity, and inherited lowstand features, all shaping the seafloor into complex geomorphologies. Previous studies have highlighted a common tidal strait depositional model with a strait-center zone in erosion and on each side a dune-bedded strait zone with 3D and 2D tidal dunes and tidal ripples. Even if the internal waves associated with and generated by the straits are widely documented, the effects of the internal waves on the seafloor need to be further investigated. The aim of this study is to unravel the combined effects of the tidal currents and the internal tides on current pattern and on the morphosedimentary features. We present a strait example based on an interdisciplinary approach using high-resolution geophysical and oceanographical data to better constrain the hydrodynamics and the processes acting on the seafloor. We focus on the Rion Strait in Greece which controls the connection between the Corinth Gulf and the Mediterranean Sea. Based on high-resolution multibeam bathymetry (MBES) over an area of 211 km 2 , we identify and quantify different morphologies by extracting bathymetric swath profiles. These results are integrated with currents data (ADCP) and CTD profiles. In addition, we use high-resolution chirp sub-bottom profiles and sparker seismic reflection profiles to document the morphology and internal architectures of the sedimentary deposits and the erosional features in the strait bottom. To complete this dataset, we analyzed Sea Surface Temperatures (SST) from satellite sensors. The Rion Strait displays complex bathymetric features without tidal dunes. At the excepted depositional location of tidal dunes, we identify an erosive area with a pool and crest morphology. This new example completes the tidal strait depositional model by a re-localization of erosion, bypass and deposition in an asymmetric strait swept by baroclinic currents. This example illustrates the key role of internal tides in straits located between a confined deep basin and an open sea.
Geological gas seepage in petroleum-bearing sedimentary basins is an important natural source of ... more Geological gas seepage in petroleum-bearing sedimentary basins is an important natural source of atmospheric methane. In methane budget models geological emissions are generally considered constant over time, not affecting decadal atmospheric methane changes. Here, we report the case of a considerable sub-decadal variation of methane seepage from one of the largest thermogenic gas seep sites in Europe, Katakolo Harbour (Western Peloponnese, Greece). Based on gas flux measurements by accumulation chamber performed in 2010 and 2018, methane emission from cracks and fissures throughout the asphalt and concrete pavement of the harbour increased about four times (from 57 to 225 kg d À 1) with emission factor changing from ~4,000 to 15,000 t km À 2 y À 1. Multiple lines of evidence, including mechanical deformation and fissuring of concrete and asphalt pavement, increased exhalation with constant fissure conditions, and no significant cracking with operating corrosion from 2004 to 2010, suggest that the methane emission increase is mainly due to intensification of subsurface gas flow (seepage) after 2010. Deep gas pressure and fault permeability variations, likely induced by the numerous earthquakes of the region, might have played a role. We estimate that if similar short-term variations of emission factor occur in large seepage areas worldwide, the global geological methane emission can significantly change, contributing to decadal changes of atmospheric methane budget.
We assessed amounts, composition and net accumulation rates every ~15days of beach macro litter (... more We assessed amounts, composition and net accumulation rates every ~15days of beach macro litter (≥2.5cm) on 4 Mediterranean beaches, on Corfu island, N. Ionian Sea, taking into account natural and anthropogenic drivers. Average net accumulation rate on all beaches was found 142±115N/100m/15d. By applying a Generalized Linear Model (GzLM) it was shown that sea transport is the dominant pathway affecting the amount and variability in beach litter loadings. Principal Component Analysis (PCA) on compositional data and indicator items discerned two more pathways of beach litter, i.e. in situ litter from beach goers and wind and/or runoff transport of litter from land. By comparing the PCA results to those from a simple item to source attribution, it is shown that regardless their source litter items arrive at beaches from various pathways. Our data provide baseline knowledge for designing monitoring strategies and for setting management targets.
Zeitschrift für Geomorphologie, Supplementary Issues, 2009
... Similar geophysical techniques have been used in underwater archaeology in order to recon-str... more ... Similar geophysical techniques have been used in underwater archaeology in order to recon-struct the ... So far, three dates have been proposed for them: (i) Thuile (1922) suggested that both these breakwaters were constructed in the Hellenistic-Roman period (ii) El ...
reece for the con n outfall, au active formed in soft layered olocene silts. The pockmarks are as... more reece for the con n outfall, au active formed in soft layered olocene silts. The pockmarks are associated with acoustic anomalies attri sediments. The pockmarks vary uring the 24 hour per three occasions, w at the three abrupt seawater te~l~erature increase ly the result of upward m s bubbles in the water column. It is further sug he earthquake was the tr mechanism and that the as expulsion was caused y the reduction in the pore vohnne in the sedi gime prior to the earthy ke. Therefore, it can be su sted that in seismi fields, earthquake prediction may be achieved by monitoring the r temperature and/or the rate of gas venting in the pockmark field. Our analysis indicates that the pockmark field in the Pa&as Gulf has formed slowly durin continuous gas venting, which is periodically being interrupted by short-duration events of enha triggered by earthquakes. * Corresponding author. from a set of oceanographical and geological data, which were collected over a pockmark field before and after the earthquake, are reported. area is located at the southeastern te the graben in the vicinity of (Fig. 1). It covers an area of 1 from the 15 to 80 m isobath (Fig. 1).
The Gulf of Corinth is the second most active continental rift in the world and thus a much-studi... more The Gulf of Corinth is the second most active continental rift in the world and thus a much-studied natural laboratory for analyzing details of rift history. A new detailed offshore seismic survey combined with previously acquired data in its least studied part, the Lechaion Gulf, shed light on the tectono-sedimentary evolution of the eastern end of the Corinth rift. This study shows that: (i) the Lechaion Gulf is the submerged northern part of the onshore Corinth-Nemea basin, (ii) they are both bounded to the south by the north dipping Klenia and Kenchreai faults, which are considered at present inactive, (iii) both the Corinth-Nemea basin and the Lechaion Gulf were formed at around between 3.6 and 4 Ma BP (middle to late Pliocene), at the same time with the Megara basin, and (iv) the Lechaion Gulf was submerged and took its present shape at around between 0.7 and 1.7 Ma BP, at the same time with the Gulf of Corinth and the Alkyonides Gulf. Furthermore, sequence stratigraphy interpretation of seismic profiles from the Lechaion Gulf revealed: (i) a total post-alpine sediment thickness of almost 3 km below the Lechaion Gulf, (ii) at least 400 m of sediments accumulated during the last 245 ka, corresponding to a mean sedimentation rate of 1 m/ka for the last 245 ka and 2.3 m/ka for the Holocene, and (iii) differential vertical movement, in the order of 4.5 km, between the bedrock under the Lechaion Gulf and the adjacent mountains yields an accumulative average slip rate of 0.9 m/ka or less, over the last 4 Ma. Therefore, for estimating more accurately the slip rates, the uplift rates, the extensional rates and the earthquake recurrence interval over the eastern end of the Corinth rift, the presently mentioned tectono-sedimentary evolution of the Lechaion Gulf must be taken into consideration.
Journal of Radioanalytical and Nuclear Chemistry, 2009
Activity concentration measurements of natural radionuclides performed by γ-ray spectrometry and ... more Activity concentration measurements of natural radionuclides performed by γ-ray spectrometry and ICP-MS in sediment samples from the Gulf of Itea and in surface soil samples collected from the surrounding area of a bauxite beneficiation plant, showed that (1) the breaker zone of the Itea Gulf, in the vicinity of the bauxite beneficiation plant, is contaminated with 238 U, 232 Th and 226 Ra, (2) the activities in sediment samples from the rest of the Gulf were at the background level, and (3) enhanced activities of the 238 U, 232 Th and 226 Ra were found in a number of soil samples due to bauxite dust deposition from the nearby beneficiation plant. The application of the optimized BCR sequential extraction procedure on the surface sediment samples showed that the U and Th were strongly bound to the sediments.
Surficial and subsurficial sediment samples derived from gravity cores, selected from the harbour... more Surficial and subsurficial sediment samples derived from gravity cores, selected from the harbour of Patras, Greece, were analyzed for grain size, water content, bulk density, specific gravity, organic carbon content and specific activities of natural radionuclides and (137)Cs. The specific activities of (232)Th, (226)Ra, (40)K and (137)Cs were measured radiometrically. The radionuclides (238)U and (232)Th were also analyzed using the INAA. The differences found between the specific activities of the natural radionuclides measured by the two methods are of no statistical significance. The sediment cores selection was based on a detailed bathymetric and marine seismic survey. Through the study of the detailed bathymetric map and the seismic profiles it was shown that ship traffic is highly influential to the harbour bathymetry. The granulometric and geotechnical properties of the sediments and therefore the specific activities of the natural radionuclides and (137)Cs seem to be controlled by the ship traffic. Relationship between radionuclide activity concentrations and granulometric/geotechnical parameters was defined after the treatment of all the analyses using R-mode factor analysis. The natural radionuclide activities are related to the fine fraction and bulk density of the sediments, while (137)Cs is mainly influenced by the organic carbon content. In addition, (238)U and (226)Ra seem to be in close relation with the heavy minerals fraction in coarse-grained sediments with high specific gravity.
Acoustic classification systems and the Sediment Trend Analysis method were used to identify and ... more Acoustic classification systems and the Sediment Trend Analysis method were used to identify and map the bed diversity in a very shallow (<3.0m), coastal lagoon, Pappas lagoon, Western Greece. Analogue acoustic data, collected by means of a 100 kHz side scan sonar system, were digitized and classified into six acoustic classes using recently developed acoustic classification systems (SonarClass, TargAn). By comparing the acoustic classes to ground truth data consisting of sediment grain size and visual inspection of the lagoon-bed, it is demonstrated that the six acoustic classes correlate well with the predominant surface sediment types and vegetation. Thus the spatial distribution of the classes can be considered to represent the spatial pattern of the sedimentary assemblages of the lagoon. The grain size trend analysis identified three dominant sediment pathways and directional trends which could be related to the predominant wind direction, the sediment influx through the inlets and the sediment supply from a small stream in the southern part of the lagoon. The integration of acoustic and sedimentological data together with advanced data processing systems leads to a better understanding of the sedimentary, morphological and biological processes in a shallow lagoon in different spatial and temporal scales and will therefore be beneficial to both sedimentological and biotic-diversity studies.
... The use of multivariate statistical methods is directed to the identification ... Furthermore... more ... The use of multivariate statistical methods is directed to the identification ... Furthermore, this paper suggests a simple methodological scheme based on multivariate techniques for studying temporal variations of hydrochemical parameters in shallow lake systems. 2. Study area. ...
Considerable seepage of natural gas occurs throughout the Katakolo Bay, both at sea and on land, ... more Considerable seepage of natural gas occurs throughout the Katakolo Bay, both at sea and on land, along the Ionian coast of Peloponnesus (Western Greece). Explosive levels of CH 4 and toxic concentrations of H 2 S accumulating in the ground, pose a severe hazard for humans and tourist infrastructures. A wide offshore and onshore gas survey, including marine remote sensing, underwater exploration by a towed instrumented system, compositional and isotopic analyses, and flux measurements of gas, allowed us to assess that: (a) gas seepage takes place along two main normal faults; (b) offshore side-scan sonographs recorded at least 823 gas bubble plumes over an area of 94,200 m 2 , at depths ranging from 5.5 to 16 m; (c) offshore and onshore seeps release the same type of thermogenic gas (δ 13 C CH 4~− 34 to − 36‰); (d) offshore gas showed increased stable carbon isotopic ratio of CO 2 and propane, which suggests enhanced biodegradation of hydrocarbons; (e) isotopic data combined with thermogenic gas generation modeling and maturity plots, suggest that the gas is related to a deep Petroleum System with Jurassic carbonate reservoirs, Triassic source rocks, and Triassic evaporites; (f) H 2 S (δ 34 S: + 2.4‰) is produced by thermochemical sulfate reduction in deep anhydrites, in contact with hydrocarbon-rich carbonates; (g) due to the shallow depth, more than 90% of CH 4 released at the seabed enters the atmosphere, consistent with theoretical bubble dissolution models, with a mean plume output of 0.12 kg d −1 ; total offshore CH 4 output was estimated in the range of 33 to 120 t y −1 ; and (h) in the onshore area at least 50 gas vents in the harbor and a large seep on the adjacent Faros hill, emit in total about 89 t CH 4 y −1. Katakolo results to be one of the biggest thermogenic gas seepage zones in Europe.
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