HIGH-RESOLUTION GEOMORPHOLOGICAL MAPPING OF THE SHALLOW CONTINENTAL SHELF WEST OF THE KAVALA BAY, NORTH AEGEAN

Σημαντικές γεωμορφολογικές δομές του ρηχού τμήματος της υφαλοκρηπίδας δυτικά του Κόλπου της Καβάλας χαρτογραφήθηκαν χρησιμοποιώντας τα δεδομένα από μια υδρογραφική αποτύπωση (τον Ιούνιο 2014) 320 ναυτικών μιλίων, η οποία περιελάμβανε υψηλής διακριτικότητας πολυδεσμική βαθυμετρική καταγραφή και διασκόπηση πυθμένα με σεισμική ανάκλαση. Αναγνωρίστηκε ένα σύστημα ρηγμάτων αποτελούμενο από ένα σετ δυο κυρίων κανονικών ρηγμάτων (καταγεγραμμένο μήκος και μετρημένο κατακόρυφο άλμα αυτών: 12 χλμ, 5 χλμ και > 40 μ, 25 μ, αντίστοιχα,) με έντονη επιφανειακή εκδήλωση στο θαλάσσιο πυθμένα, καθώς και τρία δευτερεύοντα ρήγματα νότια των κύριων ρηγμάτων, τα οποία φανερώνουν συνιζηματογενή τεκτονισμό. Η εντυπωσιακή διαφορά στις υφές των ιζημάτων που καλύπτουν αφενός το υποκείμενο ρηξιτέμαχος του βορειότερου κυρίου ρήγματος και αφετέρου την οροφή του νοτιότερου κυρίου ρήγματος δείχνει τη σημαντική επίδραση του τεκτονισμού στις ιζηματολογκές διεργασίες της περιοχής μελέτης. Όσον αφορά τις υπάρχουσες γεωμορφές, οι περισσότερο ενδιαφέρουσες είναι εκείνες των αμμωδών θινών στο βορειοανατολικό τμήμα της περιοχής μελέτης, ευρισκόμενες σε βάθη από 25 μ μέχρι τουλάχιστον 65 μ. Οι μεγάλες διαστάσεις τους καθώς και ο προσανατολισμός τους ως προς την ακτογραμμή υποδηλώνουν ως μηχανισμό σχηματισμού τους την δράση ισχυρών πυθμιαίων ρευμάτωνProminent geomorphological features of the shallow continental shelf west of the Kavala Bay (Loutra Eleftheron-Nea Peramos) were mapped using the data from a hydrographic survey (June 2014) of 320 nautical miles during which high resolution multibeam bathymetry and seismic-reflection subbottom profiling were carried out simultaneously. A fault zone comprised by a set of two primary sigmoidal gravity faults (recorded lengths and measured offsets: 12 km, 5 km and > 40 m, 25 m, respectively), with distinct expression on the seabed, and three other secondary gravity faults situated southern of the major faults, revealing synsedimentary tectonics, was identified. The striking difference between the texture of the footwall block sediments of the northern major fault and the texture of the sediments occupying the deep hanging wall block of the southern major fault emphasizes the impact of local tectonics on the sedimentary evolution of the study area. Concerning the observed bedforms, the most interesting were the sand dunes occurring at depths from 25 m to 65 m at least and occupying the northeast part of the study area. Their large dimensions and orientation in relation to the coastline position imply as a mechanism for their formation intense bottom-current activity

GEOMORPHOLOGY, SEDIMENTOLOGY AND GEOCHEMISTRY IN THE MARINE AREA BETWEEN SIFNOS AND KIMOLOS ISLANDS, GREECE

Στην ελάχιστα μελετημένη θαλάσσια περιοχή μεταξύ των νησιών Σίφνου και Κιμώλου πραγματοποιήθηκε μια εκτεταμένη ωκεανογραφική μελέτη, με σκοπό την καταγραφή της υποθαλάσσιας μορφολογίας και των χαρακτηριστικών των επιφανειακών ιζημάτων, καθώς και της πηγής προέλευσης αυτών. Έγιναν καταγραφές με πολυδεσμικό βυθόμετρο και δειγματοληψίες επιφανειακών ιζημάτων με box corer με το Ω/Κ Αιγαίο και ακολούθησαν αναλύσεις μεγέθους κόκκων, ορυκτολογίας και γεωχημείας. Ένα μεγάλο βαθυμετρικό βύθισμα εντοπίστηκε βόρεια της Κιμώλου, με μέγιστο βάθος 743 μ., που συγκεντρώνει λεπτόκοκκα ιζήματα. Η κατανομή των ιζημάτων ως προς το μέγεθος κόκκων χαρακτηρίζεται από σταδιακή μείωση του μεγέθους από νότο προς βορρά. Η ορυκτολογική σύσταση περιλαμβάνει ασβεστίτη, Mg-ασβεστίτη, αραγωνίτη, δολομίτη, χαλαζία, Κ-άστριους, πλαγιόκλαστα, αμφίβολους και αργιλικά ορυκτά. Οι κύριες ιζηματολογικές επαρχίες που αναγνωρίστηκαν είναι 1) η ρηχή περιοχή πλησίον της Κιμώλου, με υψηλό περιεχόμενο σε Si, Al, K, Rb και Ba, 2) η βαθιά περιοχή δυτικά της Σίφνου, όπου εμφανίζεται και το μεγάλο βύθισμα, που χαρακτηρίζεται από υψηλό περιεχόμενο σε Fe, Ti, Na, Mg, S, Cr, Cu, Ni, V, Zn και 3) το στενό μεταξύ Σίφνου και Κιμώλου, με υψηλότερο περιεχόμενο σε Ca, S και Sr. Στο βύθισμα αυτό, παρατηρήθηκε σημαντικός εμπλουτισμός των ιζημάτων σε μαγγάνιο, ενώ τα οξείδια του Mn φαίνεται να προσροφούν διάφορα μέταλλα.An extensive oceanographic survey was conducted in the marine area between Kimolos and Sifnos Islands, a rather poorly-studied sector of the Aegean Sea, in order to gain better understanding of submarine geomorphological features and associated sediment provenance. Multi-beam bathymetry and surface sediment sampling with a box corer were carried out on board R/V Aegaeo, followed by grain-size analysis, XRD and XRF measurements. A large circular depression was identified north of Kimolos reaching a water depth of 743 m, filled with fine grained sediments. Surface sediment distribution is characterized by gradual decrease in grain-size from silty sand to silt in a S-N direction. The mineralogical composition comprises calcite, Mgcalcite, aragonite, dolomite, quartz, K feldspars, plagioclase, amphiboles and clay minerals. Major sediment provinces identified were: (i) the shallow sector proximal to Kimolos, characterized by higher contents in Si, Al, K, Rb and Ba; (ii) the deep area west of Sifnos, including the large depression, characterized by higher contents in Fe, Ti, Na, Mg, S, Cr, Cu, Ni, V, Zn; and (iii) the south passage between Kimolos and Sifnos, which exhibits higher Ca, S, and Sr contents. Manganese enrichment was observed in and around the bathymetric depression, where Mn oxides act efficiently as scavengers of a suite of metals

Sediment transport mechanisms from the slopes and canyons to the deep basins south of Crete Island (southeast Mediterranean)

Sediment transport processes from the slopes to the deep basins were studied in the southern Cretan margin (Eastern Mediterranean) by means of swath bathymetry, seismic reflection (airgun) profiling, and gravity coring. Mud/silt turbidites, developed in structureless or laminated patterns, appear to dominate the continental slope and the 2700–3600-m deep depressions of Samaria, Messara, and Gortys. These deposits are the result of successive mass transport events and turbidity currents. Over-steepening caused by strike–slip shearing associated with extensional tectonic activity in the shallow crustal levels, shaking due to significant seismic activity, and the presence of weak sediment layers are responsible for frequent triggering of slope failures and the subsequent formation of turbidity currents on the Gavdos slope. On the Cretan slope, sediments channeled as turbidity currents through canyons proved to be the major delivery mechanism, together with debris flows. Subordinate contributions of hemipelagic sediments occur only in the Messara basin. Moreover, steep non-incised slope areas and slope-confined canyons of the Gavdos slope were found to provide comparable sediment contribution with the fluvially connected canyons of the Cretan slope. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature

Benthic foraminiferal assemblages in the severely polluted coastal environment of Drapetsona-Keratsini, Saronikos Gulf (Greece)

Surface sediments were collected from the coastal zone of Drapetsona–Keratsini (Saronikos Gulf, Greece) in December 2012 for determining the local benthic foraminiferal community, identifying their spatial distribution patterns, and evaluating the response of foraminiferal species to geochemical composition through the hierarchical cluster analysis, principal component analysis and Spearman's rho correlation. Foraminifera can be classified into three distinct assemblages associated with the granulometry, elemental geochemistry, particulate organic carbon content and degree of sediment contamination. A relatively low-diversity assemblage, dominated by stress-tolerant taxa with Ammonia tepida Bolivina spathulata and Bulimina elongata being the prevailing species, is characteristic of the silty seabed of the main part of Drapetsona coastal zone and the Keratsini Port central basin, where organic carbon content, aliphatic and polycyclic aromatic hydrocarbons concentrations and trace metal loads are greatly elevated. On the sandy bottom of the investigated area, relatively high frequencies of miliolids prevail. An epiphytic rotaliid-dominated assemblage is recorded in the slightly-polluted sedimentary bottom of the inner and western part of the Keratsini Port. © 2018 Elsevier Masson SA

Assessment of the eruptive activity and identification of the mud breccia's source in the Olimpi mud volcano field, Eastern Mediterranean

Even though the intensity and frequency of the eruptive episodes of deep-sea mud volcanoes (MVs) substantially regulate the methane fluxes into the hydrosphere and the development of the near-seafloor sulfate zone that affects the position of the gas hydrate stability zone, these factors are not yet adequately investigated. Moreover, the evaluation of the eruptive sediment's thermal maturity may provide solid documentation of the petroleum generation potential in high depths below seafloor (bsf). Hence, the present study, through the integration of sedimentary facies analysis with hydrocarbon biomarker analysis (based on the concentrations of long-chain (C25–C35) n-alkanes, hopanes and steranes), supported by swath bathymetry data, examined five sediment cores recovered from the Gelendzhik, Moscow, Milano, Leipzig and Heraklion MVs of the Olimpi mud volcano field (OMVF) on the central Mediterranean Ridge. The main objective of this investigation was to assess the ‘modern’ eruptive activity in the OMVF and identify the mud breccia's origin and mobilization depth (based on its maturity level), and the ages of the source beds. Among the studied MVs, Milano, Leipzig and Heraklion appear ‘recently’ active, while Moscow perhaps remains in dormancy for at least one century. The eruptive activity in the OMVF seems to be, generally, vigorous and persistent, while it is linked with several source beds of variable stratigraphy or environmental condition. The multiple eruptive episodes, occurring as uninterrupted events or via pulses, create conditions that perhaps favour high releases of methane into the water column as well as the growth of the gas hydrate phase near the seafloor. The identified ‘modern’ mudflows appear thermally immature for oil generation, while they most probably originate from terrestrial source beds located not deeper than 2 km bsf. A Messinian age could be suggested for the principal sources of the very soft to soft mud breccias of the OMVF, while stratigraphic horizons of Early-Middle Miocene might be proposed as the likely major sources for the firm to very stiff mud breccias of the area. © 2019 Elsevier Lt

Late Glacial and Holocene vegetation patterns of Attica: A high-resolution record from Elefsis Bay, southern Greece

The present study focuses on the palynological investigation of a sediment core (S2P) recovered from Elefsis Bay, in the western part of Attica Peninsula (southern Greece). Until now, there is quite scarce knowledge about the vegetation history of southern Greece during Late Glacial and Holocene due to a deficiency of long high-resolution pollen records. The analyzed gravity core is a unique continuous and well-dated pollen archive, providing the opportunity for the reconstruction of the plant landscape succession in southern Greece since Late Glacial. In order evidence for the vegetation response to climate oscillations and human impact to be derived, detailed analyses were conducted throughout the sedimentary sequence, spanning the last 13,500 years. The pollen data suggest that temperate deciduous, open oak woodlands of Late Glacial were fully expanded during the onset of Holocene, without any pronounced setback due to climate oscillations as it has been previously indicated by pollen archives from northern Greece. Following this period, Middle Holocene is characterized by the establishment of complex vegetation patterns, partly as the result of human activities, which seem to be the dominant vegetation shaping factor during Late Holocene. Overall, our pollen record highlights the vegetation transition during Late Glacial and Holocene in southern Greece, while offering valuable insight into the plant landscape prior to the first signs of human impact on the environment. © 2019 Elsevier Ltd and INQU

Environmental evolution of the Paliouras coastal lagoon in the eastern Thermaikos gulf (Greece) during Holocene

The integration of lithology determination, micropaleontological and molluscan analyses, scanning electron microscopy, magnetic susceptibility measurement, and radiocarbon dating contributed to the interpretation of a sedimentary succession recovered from a 870-cm long borehole drilled at the Paliouras coastal lagoon in the eastern Thermaikos gulf (Greece). In this way, the reconstruction of the creation and evolution of the lagoon during the last 8000 years was accomplished. Four main evolutionary phases are identified: (1) initially, the pre-Holocene basement of the study area was inundated during the early Holocene marine transgression; (2) since ~ 8000–7900 cal yr BP an inner lagoon had been formed in the Paliouras coastal plain, within a rather restricted environment characterized by a Haynesina germanica, Cerastoderma glaucum and Hydrobia sp. assemblage, relatively high sediment magnetic susceptibility and an intense presence of abnormal foraminiferal tests and lenticular gypsum crystals; (3) during 7600–6900 cal yr BP, the inner lagoon presented a transition to an open system, clearly connected to the sea and characterized by an Ammonia beccarii, Aubignyna perlucida, and miliolids assemblage, more diversified molluscan fauna, minimum sediment magnetic susceptibility and the occurrence of lenticular gypsum aggregates; and finally (4) since ~ 5900 cal yr BP to the present time, the lagoon water body appears isolated from the marine environment, except of occasional seawater intrusions. The proposed evolutionary scenario for the Paliouras coastal lagoon is in accordance with the existing models of the sea level rise in the Aegean coastal areas concerning the time span before 4000 yr BP and the mid-late Holocene climate events. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature

Coupling plankton - sediment trap - surface sediment coccolithophore regime in the North Aegean Sea (NE Mediterranean)

Quantitative coccolithophore analyses were performed on data of 2011–2015 dataset derived from the examination of plankton samples (until 100 m water depth), the sinking particulate matter (collected by a time series sediment trap) and surface and core sediments of the North Aegean Sea sampling site M2 (Athos Basin, NE Mediterranean). The aim was to achieve a better understanding of the potential modifications of the coccolithophore assemblage between the surface waters (plankton), the water column (sidocoenosis) and the underlying sediment (thanatocoenosis). Sediment trap calcareous nannoplankton multiannual mean fluxes (20 × 108 coccoliths m2 day−1) documented similar values to the accumulation rates recorded in the surface sediment (23.6 × 108 coccoliths m−2 day−1), whereas within the last 500 years the rates have ranged from 2.19 × 108 to 5.4 × 108 coccoliths m−2 day−1. The dominant species in all sampling types was Emiliania huxleyi, reaching in some cases striking relative abundances of 85–90%. Morphometric analyses on E. huxleyi coccoliths documented the presence of a lightly calcified morphotype in the water column and sediment trap samples in addition to the seasonal occurrence of heavier calcified E. huxleyi coccoliths, indicating enhanced Black Sea water inflows during May 2011, February 2015 and October 2015. However, such a signal was not preserved in the surface sediment assemblage mostly due to processes of diagenetic calcite overgrowth. Notably, Florisphaera profunda was not included in the upper water column plankton assemblage but in the sediment traps and surface sediments. Thus, it is presumed to flourish in nutrient-enriched layers below the sampled 100 m water column depth. Several fragile Syracosphaeraceae and holococcolithophore species and the delicate Algirosphaera robusta were not present in the sinking assemblage or on the seafloor; however, the main features of the living assemblages were generally preserved. The recorded high relative abundances of E. huxleyi (~60%) in the sediment were in accordance with positive North Atlantic Oscillation (NAO) shifts during recent production of dense water masses in the North Aegean. © 2019 Elsevier B.V

Coccolithophore export in three deep-sea sites of the Aegean and Ionian Seas (Eastern Mediterranean): Biogeographical patterns and biogenic carbonate fluxes

Coccolithophore export fluxes were investigated via the analysis of sinking matter, obtained from Eastern Mediterranean time-series sediment traps moored in three open sites of the north-eastern Mediterranean Sea located in the Athos Basin of North Aegean (M2 site), Cretan Sea of South Aegean (M3 site) and at Ionian Sea (Nestor site). The aim of our study was to determine the spatial, temporal and seasonal variability in coccolithophore fluxes, as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process. Data from an additional time-series sediment trap located in the southwestern Black Sea were also considered for the comparison of the oligotrophic Eastern Mediterranean setting with the eutrophic Black Sea. Coccolithophore fluxes revealed a highly seasonal pattern during February–March in the North Aegean (peak in late February 2015: 85.6 x 105 coccospheres m−2 day−1; 27.9 x 108 coccoliths m−2 day−1), during March–May in the Cretan Sea (peak in late March 2015: 33.7 x 105 coccospheres m−2 day−1; 19.5 x 108 coccoliths m−2 day−1) and during February–March and May–June in the Ionian Sea (peak in late May 2012: 14.3 x 105 coccospheres m−2 day−1; 1.53 x 108 coccoliths m−2 day−1). The recorded maxima coincide with low sea surface temperatures, increased precipitation and high PIC fluxes. Coccosphere fluxes were dominated by Emiliania huxleyi comprising ~70% of the total abundance, in the North Aegean and ~50% in the Cretan and Ionian Seas. Syracosphaera pulchra was also prominent in the study sites, where its abundance reached 14% in the North Aegean and ~10% in the Cretan and Ionian Seas respectively. Florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three Eastern Mediterranean sites (~25% in North Aegean, ~20% in Cretan and Ionian Seas), while Algirosphaera robusta and Umbilicosphaera sibogae were the most abundant among the minor taxa. The North Aegean Sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of E. huxleyi during winter (February–March) (>95% of the total abundance). In contrast to the Eastern Mediterranean sediment traps, the time-series data from the Black Sea showed presence of monospecific E. huxleyi assemblage increasing its abundance during late September–November (max 320 x 105 coccospheres m−2 day−1; at least 7.79 x 108 coccoliths m−2 day−1, coccolith flux derived only from coccospheres converted to coccoliths). In the Eastern Mediterranean, biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas, with the Black Sea coccolithophore CaCO3 flux being the lowest due to low the E. huxleyi coccolith mass. Overall, in the North Aegean Sea, coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing, riverine inputs and Black Sea water inflows, while the fertilization and/or formation of fast-sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the Cretan and Ionian Seas. The intercomparison of the coccolith export fluxes in the studied NE-SW mooring transects implies a north-south and east-west decreasing pattern, depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas. © 2019 Elsevier Lt

Hydrodynamic, neotectonic and climatic control of the evolution of a barrier beach in the microtidal environment of the NE Ionian Sea (eastern Mediterranean)

The existence of barrier beaches is crucial, as they act as a buffer zone to the associated wetlands, whilst they are sensitive to climate change. The present study offers an insight into the processes controlling the formation and evolution of the Gyra barrier beach (NW coast of the island of Lefkada) in the microtidal, tectonically very active Ionian Sea under the influence of regional climate change and human interference. Such investigations are sparse in the literature. Existing information regarding regional geology, sediment availability and human intervention is combined with the collection of geophysical data, field observations and simulations of nearshore hydro- and sediment dynamics, analysis of climatic variations with respect to offshore wind/wave patterns (including storminess), in situ measurements of recent morphometric changes (2006–2008) and historical shoreline changes (since the 1960s). The recent formation and evolution (mostly under retreat) of the Gyra barrier beach is shown to be the combined result of the regional seismotectonic setting, relative increase of sea level, coastal sediment transport patterns, as well as human impact (negative) on primarily terrestrial sediment influxes. The current erosional trend of the barrier beach is associated with a shift in the wind and wave direction (from SW to NW) of extreme storm events in the Ionian Sea since the 1980s. The regional climatic variations of the last decades are well correlated with the trend of the North Atlantic Oscillation. © 2014, Springer-Verlag Berlin Heidelberg