South Aegean Sea Research Articles

Wavelet-Based Rapid Estimation of Earthquake Magnitude Oriented to Early Warning

The main goal of an earthquake early warning system (EEWS) is to estimate the magnitude of an underway rupture from the first few seconds in order to allow hazard assessment and mitigation before destructive events occur. This letter investigates the application of a wavelet-based algorithm for local magnitude estimation in the South Aegean Sea (focusing on Crete Island) which is covered by a sparse seismological network. A relation between the first few seconds of the first-arriving energy at the surface, the P wave, and the local magnitude of the earthquake has been developed for the area of interest. Results show that the errors produced by the proposed method present less scattering than relevant magnitude rapid estimation methods. It is the first time that such a method is applied in a sparse seismological network since all the previous studies took place in high-density networks. This fact expands the applicability of EEWS and also provides an alternative magnitude estimator for the currently developed EEWS.

Hyperbenthic community structure over oligotrophic continental shelves and upper slopes: Crete (South Aegean Sea, NE Mediterranean)

The community structure of hyperbenthos on continental shelves and upper slopes of oligotrophic areas have been little studied. The present study, located in the eastern Mediterranean (Heraklion Bay, Crete) gives the first description of this using samples collected at depths ranging between 50 and 300 m in two seasonal occasions (March and September 2001) using a modified hyperbenthic sledge (0.5 mm mesh size) specifically designed to resuspend the sediment surface and to sample simultaneously the hyperbenthic macrofauna. The analysis revealed 96 different taxa (Peracarida and Decapoda) with densities ranging from 198 to 2618 ind 100 m−2 and indicated the presence of a clear zonation of the hyperbenthic communities along a depth gradient as well as different diel and seasonal adaptations to the prevailing environmental conditions of the community structure. Artificial resuspension of the sediment surface revealed that the highest proportion of the hyperbenthic macrofauna collected in this oligotrophic environment (74–100 %) was found to reside at the sediment–water interface (0–0.05 m). This demersal behaviour seems to be a response to high light levels close to the seabed and availability of food sources associated with the sediment surface.

Microplanktic assemblages (sarcodines and alveolates) in the central and southeastern Aegean Sea (NE Mediterranean)

Spatial changes in the structure of microplanktic assemblages (sarcodines and alveolates) in the surface waters of coastal regions in the central and southeastern Aegean Sea were estimated during late summer to early autumn. Tintinnidae (Ciliophora), as well, Acanthometridae (Radiolaria) and Globiderinidae (Foraminifera) exhibited a higher abundance in the central Aegean Sea, compared to that in the more oligotrophic southeastern area of the same sea. Multivariate analysis revealed that the samples from the eastern Cretan Sea (South Aegean Sea) were highly distinguished from all the others and showed the highest densities of polycystines (Radiolaria), specifically of the families Thalassicollidae, Thalassosphaeridae, Sphaerozoidae (Collodaria), as well as of Actinommidae (Spumellaria) and Theoperidae (Nassellaria). In addition, the families Ceratiaceae and Prorocentraceae (Dinoflagellata) were more abundant in the southeastern than in the central Aegean Sea. It is indicated that the hydrographic conditions prevailing in the eastern Cretan Sea affected the structure of the microplanktic community in the surface layer. It is proposed that the assemblage of the identified radiolarian families belonging to Collodaria, Spumellaria (S) and Nassellaria (N), with a high S/N ratio, could be used as biological proxy of weak upwelling systems in the warm stratified waters of the oligotrophic eastern Mediterranean. Key words: Eastern Mediterranean, microplankton, sarcodines, alveolates, abundance, oligotrophic ecosystems.

Modelling of tsunami generated by the giant Late Bronze Age eruption of Thera, South Aegean Sea, Greece

Tsunami generated by the Late Bronze Age (LBA) eruption of Thera were simulated using synthetic tide records produced for selected nearshore (∼20 m depths) sites of northern Crete, the Cyclades Islands, SW Turkey and Sicily. Inundation distances inland were also calculated along northern Crete. Modelling was performed by incorporating fully non-linear Boussinesq wave theory with two tsunamigenic mechanisms. The first involved the entry of pyroclastic flows into the sea, assuming a thick (55 m; 30 km3) flow entering the sea along the south coast of Thera in three different directions all directed towards northern Crete, then a thin pyroclastic flow (1 m; 1.2 km3) entering the sea along the north coast of Thera directed towards the Cyclades Islands. Flows were modelled as a solid block that slowly decelerates along a horizontal surface. The second mechanism assumed caldera collapse, of 19 km3 and 34 km3 modelled as a dynamic landslide producing rapid vertical displacements. Calculated nearshore wave amplitudes varied from a few metres to 28 m along northern Crete from pyroclastic flows, and up to 19 m from caldera collapse (34 km3 volume). Inundation distances on Crete were 250–450 m. Waves produced by pyroclastic flows were highly focused, however, as a function of sea entry direction. Smaller volume pyroclastic flows produced nearshore wave amplitudes up to 4 m in the Cyclades islands north of Thera. Wave amplitudes in the Cyclades from smaller volume caldera collapse (19 km3) were up to 24 m, whereas in SW Turkey were as low as 2.1 and 0.8 m (Didim and Fethye where LBA tsunami deposits have been found). Wave amplitudes for the larger volume caldera collapse (34 km3) were generally 2.5–3 times larger than those generated by the smaller volume collapse (19 km3). These results provide estimates for understanding possible consequences of tsunami impact in LBA coastal zones, thus providing criteria at archaeological sites for detecting inundation damage, as well as for contemporary hazard assessment; they also provide additional criteria for deciphering homogenite layers in the abyssal stratigraphy of the Ionian and eastern Mediterranean Seas.

Allometric equations for aboveground biomass estimation by size class for Pinus brutia Ten. trees growing in North and South Aegean Islands, Greece

Empirical allometric equations relating biomass of aboveground components to dendrometric variables for Pinus brutia Ten. trees are derived in this paper. They are based on data collected from Lesvos (North Aegean Sea) and Crete (South Aegean Sea) Islands. Comparisons to published equations for the same species growing in northwestern and southeastern Turkey, for Pinus nigra A. growing in Turkey and Pinus halepensis Mill. found in Western Aegean (island of Evia), are also presented. The biomass of branches from destructively sampled trees (twelve in Crete and six in Lesvos) was divided into four size classes (0–0.63 cm, 0.64–2.5 cm, 2.51–7.61 cm, and 7.62–22.8 cm). Tree crown biomass was calculated as the sum of the biomass in the four classes plus the fraction of stem above crown base. Over bark stem biomass was estimated through bole volume conversion based on wood density. The results showed clearly that, for a given diameter, the Cretan trees had more crown biomass and a higher share of small branches than trees on Lesvos, probably due to differences in environment and stand structure. Comparisons to published diameter versus crown biomass equations reveal a lower crown biomass for Turkish sites of Calabrian pine and Aleppo pine on Evia Island, while only Turkish Black pine seems to be comparable to the Calabrian pine on Crete. The derived allometries can be used for landscape fire behavior modeling, for ecophysiological studies and for the Kyoto protocol requirements of carbon changes in Pinus brutia Ten. forests located in northern and southern Greek sites.

Tornado activity in Greece within the 20th century

Abstract. Tornado activity is associated with extreme convective weather which can cause extended damage and even in some cases the loss of life. The complex inland terrain of Greece along with the Ionian Sea at the west and the Aegean Sea at the east appear to be a favorable area for fury phenomena such as tornadoes, waterspouts and funnel clouds. In this study, the spatial and temporal variability of tornado activity in Greece for the period 1900–1999 are presented. The spatial distribution of tornadoes, waterspouts and funnel clouds reveals the vulnerability of specific geographical areas, such as the west Greece and the south Aegean Sea. As far as the intra annual variability is concerned, the maximum of tornado activity dominates within the cold period of the year (October–March) while according to the daily distribution, tornadoes happen frequently during the warm hours of the day. It is remarkable to mention that in Greece, within the 20th century, the tornado activity caused the loss of 4 lifes, the injury of 40 people and numerous damages on human constructions and cultivations.

Sponge epibionts on ecosystem-engineering ascidians: The case of Microcosmus sabatieri

The study of epibionts on habitat engineering ascidians is of increasing interest because changes in the population structure of the latter may affect associated communities, especially in the case of commercially exploited species. The solitary ascidian Microcosmus sabatieri lives on rocky cliffs in the Eastern Mediterranean and is harvested in certain Aegean areas. Its hard, wrinkled tunic is usually fouled by various epibionts both sessile and motile. Sponges are an important component of this complex and their biomass may be higher than that of the ascidian itself, strongly affecting diversity and abundance of the motile epifauna. The aim of this study was to examine in detail the structure of the epibiotic sponge assemblage on ascidians collected from their main fishing grounds in the South Aegean Sea. A rich (41 species) and taxonomically diverse sponge assemblage was found, while only eight species contributed 80% of the total sponge cover. Most of the epibiotic sponges commonly grow on the surrounding sublittoral cliffs. The encrusting sponge growth form prevailed in cover of the ascidian tunic, while two massive species dominated in terms of frequency of appearance and abundance. Ascidian dimensions, weight and volume were significantly correlated with sponge diversity, abundance and cover area, thus structuring the epibiotic sponge assemblage. Spatial patterns in sponge cover were not clear, but a general declining NW to SE trend in sponge richness, abundance and cover appeared in accordance with previous records. Sponge distribution on the ascidian tunic presented a clear pattern related with characteristic features of the ascidian: the posterior zone supported the richest and most expansive sponge fauna. The ecosystem-engineering process performed by the ascidian is enhanced by the diverse epibiotic sponge assemblage, thus further increasing habitat complexity in this space-limited, temperate, sublittoral, rocky environment.

Tetrahydrofuran Acetogenins from Laurencia glandulifera

Five new C(15) acetogenin en-ynes (1-5) with a rare tetrahydrofuran moiety and a linear biosynthetic precursor (6) were isolated from an organic extract of Laurencia glandulifera, collected from the island of Crete in the south Aegean Sea. The structures of the new natural products, as well as their relative configuration, were established by means of spectroscopic data analysis. The cytotoxicity of the isolated natural products was evaluated against five human tumor cell lines.

Origin and distribution of the terrigenous component of the unconsolidated surface sediment of the Aegean floor: A synthesis

The Aegean Sea covers an area of some 160×10 3 km 2 and receives the water/sediment fluxes from a mountainous drainage basin of >200×10 3 km 2. On the basis of its morphodynamic characteristics, the Aegean Basin could be divided into: (1) the North Aegean Sea, an elongated region (trending between N50° and N70°) including the extensive northern shelves and the Deep Aegean Trough; (2) the Central Aegean, which includes: the Cyclades Plateau, a relatively shallow (average depth <350 m) submerged platform, surrounded by small basins (up to 1000 m depth), including also the relatively extended eastern shelf of Asia Minor, and (3) the Southern Aegean Sea, located southwards of the Hellenic volcanic arc, which presents the characteristics of a true back-arc basin (the Cretan Sea). The surficial unconsolidated sediments of the north Aegean floor are dominated by the terrigenous component (from 50% up to >90%) due to the large terrigenous riverine fluxes. The South Aegean presents high percentages (>50%) of biogenic material, due to the small terrigenous inputs and despite the fact that it is more oligotrophic than the North Aegean. The Central Aegean presents a transitional character with the terrigenous influxes being imported along its eastern part and quantitatively being in between those of the North and South Aegean Sea sub-regions. The coarse-grained materials in shallow (shelf) areas are attributed to ‘relict’ deposits, while those in large water depths are almost exclusively biogenic products. The offshore distribution of the fine-grained terrigenous material is dominated by the overall circulation pattern, while meso-scale eddies may, locally, either enhance (anticyclones) or reduce (cyclones) settling rates. Moreover, the spatial distribution of the predominant clay minerals (illite and smectite) and of kaolinite and chlorite is governed by the lithology and proximity to land source areas, the water circulation and the processes of differential settling and flocculation. Overall, the North Aegean is characterised by sedimentation processes similar to those of a ‘continental margin’, primarily neritic and secondarily hemipelagic, the Central Aegean region mostly by hemipelagic and the South Aegean, behaving more like an ‘oceanic margin’, mostly by pelagic processes.

Stable isotopic composition of Holocene benthic foraminifers from the Eastern Mediterranean Sea: Past changes in productivity and deep water oxygenation

Temporal and regional changes in paleoproductivity and paleoceanography in the eastern Mediterranean Sea during the past 12 kyr were reconstructed on the basis of the stable oxygen and carbon isotopic composition of the epibenthic Planulina ariminensis and the shallow endobenthic Uvigerina mediterranea from three sediment cores of the Aegean Sea (GeoTü SL148, 1094 m water depth; GeoTü SL123, 728 m water depth) and Levantine Basin (GeoTü SL112, 892 m water depth). The end of the Younger Dryas is characterized by high δ 18O values, indicating enhanced salinities and low temperatures of deep water masses at all investigated sites. With the onset of the Holocene, δ 18O records show a continuous decrease towards the onset of sapropel S1 formation, mainly caused by a freshening and warming of surface waters at deep water formation sites. In the middle and late Holocene, the similarity of δ 18O values from the southern Aegean Sea and Levantine Basin suggests the influence of isotopically identical deep water masses. By contrast, slightly higher δ 18O values are observed in the northern Aegean Sea, which probably point to lower temperatures of North Aegean deep waters. The epifaunal δ 13C records reveal clear changes in sources and residence times of eastern Mediterranean deep waters associated with the period of S1 formation. Available data for the early and late phase of sapropel S1 formation and for the interruption around 8.2 kyr display decreases by 0.5 and 1.5‰, indicating the slow-down of deep water circulation and enhanced riverine input of isotopically light dissolved inorganic carbon from terrestrial sources into the eastern Mediterranean Sea. The decrease in epifaunal δ 13C signals is particularly expressed in the southern Aegean Sea and Levantine Basin, while it is less pronounced in the northern Aegean Sea. This points to a strong reduction in deep water exchange rates in the southern areas, but the persistence of local deep water formation in the northern Aegean Sea. The δ 13C values of U. mediterranea reveal temporal and regional differences in paleoproductivity during the past 12 kyr, with rather eutrophic and mesotrophic conditions in the North Aegean Sea and southeast Levantine Basin, respectively, while the South Aegean Sea is characterized by rather oligotrophic conditions. After S1 formation, increasing δ 13C values reflect a progressive decrease in surface water productivity in the eastern Mediterranean Sea during the middle and late Holocene. In the northern Aegean Sea, this time interval is marked by repetitive changes in organic matter fluxes documented by significant fluctuations in the δ 13C signal of U. mediterranea on millennial- to multi-centennial time scales. These fluctuations can be linked to short-term changes in river runoff driven by northern hemisphere climatic variability.

Biogeographic patterns of tenebrionid beetles (Coleoptera, Tenebrionidae) on four island groups in the south Aegean Sea

New records on Tenebrionidae from four island groups of the southern Aegean (Santorini, Astypalaia, Nisyros and Kalymnos, with their satellite islets – 26 islands in total) allowed investigation of the biogeography of the taxon in the area. All tenebrionid records from small islets are new, with the exception of those from Pserimos and the satellite islets of Santorini. Chorological and nestedness analyses, species‐area relationships and various measures of faunal similarity based on binary and quantitative data matrices were applied in order to explore biogeographic patterns. The Anatolian and east Mediterranean faunal elements dominate on the island groups of Kalymnos and Nisyros, with a considerable decrease on Astypalaia and Santorini, where circum‐Mediterranean elements prevail. Analyses of faunal similarities clustered together the well defined island groups of Santorini and Astypalaia, while Kalymnos and Nisyros groups were clustered together rather vaguely. Astypalaia and Santorini were also the most nested island groups in the studied area. The biogeographic position of Astypalaia within the central Aegean islands is well supported by the data.

The anatomy and provenance of thick volcaniclastic flows in the Cretan Basin, South Aegean Sea

Santorini volcano has been the largest source of volcaniclastic sediment in the Eastern Mediterranean during the late Quaternary. A dozen cores from the Cretan Basin, south of Santorini, have sampled two megabeds that consist of gravity emplaced volcaniclastic sequences. The uppermost megabed U consists of a succession of five (U 5–U 1) base cut out turbiditic units. Lower megabed A is a single turbiditic event. Only the uppermost U 2 and U 1 turbidites are separated from the underlying beds by hemipelagic marls. The texture and composition of the U and A megabeds closely match the texture and composition of the fine, vitric ash of the “Minoan” deposits on Santorini islands, dating from about 3500 yr BP. These megabeds are therefore attributed to rapid accumulation of separate gravity flows fed by the “Minoan” eruption, except for the upper U 2 and U 1 turbidites deposited from subsequent gravity flows transporting eroded volcaniclastic sediments. With the exception of the margin south of Santorini, dozens of cores retrieved around the margins of the Cretan Basin have a continuous late Quaternary succession that shows no evidence for massive sediment remobilization into the deeper basin, including the passage of the “Minoan” tsunami. Extensive high-resolution 3.5 kHz records revealed the acoustic character, architecture and distribution of the U and A megabeds and four underlying late Quaternary volcanogenic megabeds in the Cretan Basin. The acoustic facies of megabeds are typical of megaturbidites and consist of an upper, transparent, lower velocity layer that corresponds to the fine-grained upper turbiditic silt and clay section and a lower, strongly reflective higher velocity section that corresponds to the lowest, coarser-grained base of the turbidite that is developed over a sharp erosional surface. Penetration of the high-resolution records reveals the existence of at least six megabeds. Correlation with core lithology and the physical properties of the various lithofacies, including down-core velocity profiles, has allowed us to determine the thickness and volumes of the upper four megabeds which are: U ≤ 9 m thick, volume 3.7 km 3; A ≤ 25 m thick, volume 12.2 km 3; B ≤ 22 m thick, volume 10.3 km 3; C ≤ 15 m thick, volume 8 km 3. These thick megabeds are the uppermost products of repeated explosive eruption of Santorini in the late Quaternary. Calculated sedimentation rates from and after the “Minoan” eruption are 9.4 m/1000 yr that rise to over 15.7 m/1000 yr if megabed B was also deposited during this eruption.

Clay minerals in late glacial and Holocene sediments of the northern and southern Aegean Sea

Different source areas, oceanography and climate regimes influenced the clay mineral assemblages and grain size distribution of two sediment cores from the North and South Aegean Sea during the last glacial and the Holocene. In the North Aegean Sea, clay mineral composition is mainly controlled by sea level evolution, melting of southeastern European glaciers, and establishment of the connection between the Black Sea and Aegean Sea. The long-term development of clay mineral assemblages in the South Aegean Sea reflects changes in the Nile discharge and African dust input. At this site, the establishment of pluvial conditions in the Nile catchment during the early to middle Holocene resulted in a substantial rise in smectite/illite ratios. In the late Holocene, stepwise aridification of the southern borderlands caused an increase in windblown sediment material and a decrease in Nile suspended material. The clay mineral records exhibit periodic millennial-scale fluctuations. In the North Aegean Sea, the changes are centred at a period of 1.3–1.8 ka and can be attributed to short-term climate and weathering changes in the northern borderlands. The changes in the South Aegean Sea are centred at periods of 3.2–4.3, 1.9–2.4 and 1.3–1.7 ka reflecting short-term changes in wind strength and Northeast African hydrology.

A new record of the Lessepsian invasive fish Etrumeus teres (Osteichthyes: Clupeidae) in the Mediterranean Sea (Aegean, Greece)

The Lessepsian invasive fish Etrumeus teres was recorded for the first time off Crete, Greece in July 2005. Their abundance suggests that the species may become of commercial importance in the south Aegean Sea.

Spatial variability of meiofaunal communities at areas of contrasting depth and productivity in the Aegean Sea (NE Mediterranean)

The abundance and community structure of metazoan meiofauna were studied in deep-sea sediments from the north and south Aegean Sea (Eastern Mediterranean) in summer 1997 and spring 1998. The two areas varied in their surface primary productivity with the northern area being more productive. Meiofaunal densities displayed strong spatial variability while no temporal changes were observed. Total metazoan density ranged from 128 to 1251 ind./10 cm 2, with significantly higher values in the north. Meiofaunal biomass ranged from 27 to 391 μgC/10 cm 2 with higher values also in the north. At all stations nematodes dominated the community, comprising on average more than 91% of the total abundance. On a broad scale, meiofaunal densities displayed a positive correlation with food availability (sediment–bound chloroplastic pigments, carbohydrates and lipids); carbon mineralization (an indicator of organic matter turnover) was significantly higher in the northern Aegean, providing evidence of high organic–matter input and intense benthic–pelagic coupling. The spatial structure of the nematode community indicated that the two areas were similar in terms of their dominant genera ( Halalaimus, Acantholaimus, and Thalassomonhystera).

Pelagic-Benthic Coupling and Diagenesis of Nucleic Acids in a Deep-Sea Continental Margin and an Open-Slope System of the Eastern Mediterranean

Downward fluxes of nucleic acids adsorbed onto settling particles play a key role in the supply of organic phosphorus and genetic material to the ocean interior. However, information on pelagic-benthic coupling, diagenesis, and processes controlling nucleic acid preservation in deep-sea sediments is practically nonexistent. In this study, we compared nucleic acid fluxes, sedimentary DNA and RNA concentrations, and the enzymatically hydrolyzable fraction of DNA in a bathyal continental margin (North Aegean Sea) and an open-sea system (South Aegean Sea) of the Eastern Mediterranean. The two systems displayed contrasting patterns of nucleic acid fluxes, which increased significantly with depth in the North Aegean Sea and decreased with depth in the South Aegean Sea. These results suggest that in continental margin and open-ocean systems different processes control the nucleic acid supply to the sea floor. Differences in nucleic acid fluxes were reflected by nucleic acid concentrations in the sediments, which reached extremely high values in the North Aegean Sea. In this system, a large fraction of DNA may be buried, as suggested by the large fraction of DNA resistant to nuclease degradation and by estimates of burial efficiency (ca. eight times higher in the North than in the South Aegean Sea). Overall, the results reported here suggest that the preservation of DNA in deeper sediment layers may be favored in benthic systems characterized by high sedimentation rates.

Soils developed on volcanic materials in the island of Thera, Greece

Samples were taken of soils formed on volcanic material, primarily composed of rhyodacitic pumice, on the island of Thera, Greece (South Aegean Sea, Southeastern Mediterranean), and analyses for physical and chemical properties carried out. These soils are characterised as having a coarse texture, low organic matter content, low cation exchange capacity (CEC) and soil moisture retention, but a high pH despite the acidic nature of the parent material. Extraction with sodium dithionite–citrate, acid ammonium oxalate, sodium pyrophosphate and hot 0.5 M NaOH showed that, in contrast to soils usually forming on volcanic material worldwide, soils lack noncrystalline minerals like allophane, imogolite, ferrihydrite and iron and aluminium humus complexes. The only noncrystalline mineral present and, in great quantities, is amorphous silica. Winds, prevailing practically all year round, transfer droplets of seawater to these soils which in combination with the great porosity, relatively high sodium content of the parent material and low rainfall are the primary factors in the poor development of these soils and high pH. No andic properties are apparent and, hence, these soils cannot be classified as Andisols. The major factors determining soil genesis on the island of Thera would appear to be the nature of the parent material and the climate.

Objective climatology of 500-hPa cyclones in central and east mediterranean region during warm-dry period of the year

¶An Objective 500-hPa cyclone detection and analysis is performed during the warm-dry period (16 April to 15 October) of the year for the Central and Eastern Mediterranean Region (30° N–50° N, 5° E–35° E). The 40-year NCEP/NCAR reanalyzes gridded data of geopotential height and temperature employed in the study, enable a climatic approach with a spatial (2.5°×2.5°) and a 6-hour temporal (00, 06, 12, 18 UTC) resolution. The occurrence frequency for the entire region shows a high interannual variability without significant trends. The frequency maximization over land in the middle of the warm period indicates a possible relationship with land-air temperature difference. Three primary activity centers (Turkey, Black Sea and Genoa) are objectively determined in the frequency domain as local maxima and their intensity is assessed in terms of average geopotential height and temperature values. The Turkey center, though the most frequent, consists of shallow lows in contrast to the Black Sea center, which is second in frequency, but on average, contains the deepest lows amongst the three. The Genoa center, which comes third in frequency, shows the highest variability in the intensity of the lows. Frequency distributions in the area, during the three sub periods (Early, Middle and Late Warm Period) and during the four synoptic hours, provide insight in to the origins of these systems at the three locations and reveal secondary centers, such as the centers in the Adriatic (at 18 UTC), Northern Greece (during Middle Warm Period) and the South Aegean Sea (during Late Warm Period).

Spatial and temporal variability of tropospheric ozone (O3) in the boundary layer above the Aegean Sea (eastern Mediterranean)

To study the spatial and temporal variability of tropospheric ozone in the marine boundary layer over the Aegean Sea (eastern Mediterranean), an O3 analyzer has been installed onboard of a passenger vessel traveling on a regular basis in the Aegean Sea (from Heraklion/Crete 35°30′N, 25°13′E to Thessaloniki 40°64′N, 22°97′E) during a period of 14 months (August 1999 to November 2000). In addition, O3 data have been obtained on a daily basis at the regional background station of Finokalia (Crete; 35°30′N, 25°70′E) since September 1997, short‐term measurements of O3 were performed over Crete during the PAUR II campaign (May 1999), and the first O3 data from a rural area (40°32′N, 23°50′E) close to Thessaloniki at the north of Greece have been collected from March 2000 to January 2001. This survey extensive points out the existence of a well‐defined seasonal cycle in boundary layer O3 with maximum in summer both above the Aegean Sea and at Finokalia. However, the seasonal signal (defined as the summer/winter ratio) is not constant and varies as a function of air mass origin from 1.33 to 1.15 for the N‐NE and SW‐S sectors, respectively, in line with the geographical location of the O3 precursor sources. Our data show the absence of any significant longitudinal gradient over Crete at least during spring and autumn and the absence of significant latitudinal gradient between the north and south Aegean Sea during all seasons for air masses having similar origin. The above results indicate that long‐range transport is the main factor accounting for the elevated O3 levels above the eastern Mediterranean Sea. Thus (1) O3 data from Finokalia, where the longest time series are available for the area, have regional significance and (2) over the entire Aegean basin, ozone values are above the 32 ppbv European Union (EU) phytotoxicity limit throughout the year and above the 53 ppbv EU health protection limit most of the time during the dry season of the year. The very significant correlation between black carbon (BC) and O3 observed during an intensive campaign in May 2000 provides an indication that the high O3 concentrations at Finokalia resulted from ageing of air masses strongly affected by combustion processes.

Trends in the abundance of demersal species in the southern Aegean Sea

The present work identifies trends in the abundance of the main demersal species of the South Aegean Sea utilising catch and effort data derived from an international Mediterranean bottom trawl survey (MEDITS). The experimental surveys were accomplished annually from 1994 to 2000 on 61 pre-defined sampling stations. Selection of stations was based on a depth-stratified random sampling scheme that included five depth strata: 10-50, 50-100, 100-200, 200-500 and 500-800 m. The results suggest the existence of a general increasing trend in the biomass of the demersal species, particularly at the 10-50 m and 500-800 m depth strata. Findings are discussed in relation to the fisheries exploitation pattern and productivity of the area.