NW Aegean Sea Research Articles

Population dynamics of Melicertus kerathurus (Decapoda: Penaeidae) in Thermaikos Gulf (N. Aegean Sea)

The east Atlantic-Mediterranean penaeid Melicertus kerathurus constitutes a valuable resource for Mediterranean fisheries. In recent years, its world production is almost totally based on the yields from Greece and Tunisia. A two-year study of prawn stock in Thermaikos Gulf (NW Aegean Sea) provided information on age, growth and mortality of the species. M. kerathurus exhibits a marked sexual growth dimorphism, with females showing an overall wider size range and greater size than males. Mean monthly size, CL max were also in favor of females. Monthly age classes varied from one to four for females and from one to three for males, and corresponded to three generations (0 +, 1 +, 2 +). New generation (0 +) cohorts recruited into fishery in waves, from late summer to February. According to the von Bertalanffy growth curve, females grow larger than males, but there is a prominent seasonal growth oscillation in both sexes (females: CL ∞ = 62.48, K = 1.15, C = 0.87, WP = 0.16, Rn = 0.170; males: CL ∞ = 47.78, K = 1.28, C = 0.97, WP = 0.12, Rn = 0.205). Growth performance indices ( φ′, φ) and longevity were in favor of females. K values for both sexes in Thermaikos Gulf are the highest reported for the species, suggesting a higher growth rate and a lower longevity. Estimated values for total, natural and fishery mortality were greater in males. In both sexes, an exploitation rate E > 0.5 was found, implying an intense fishing impact on M. kerathurus stock in Thermaikos Gulf. Intense exploitation in other parts of the Mediterranean and eastern Atlantic, along with the replacement of the species by Eritrean penaeid prawns in the eastern Mediterranean, has resulted in a severe reduction in catches, in most countries. Thus, existing stocks of M. kerathurus should be considered as potentially endangered, and species-specific initiatives towards sustainable management of this resource should be implemented.

Parasitic infracommunities of the Aegean wall lizard Podarcis erhardii (Lacertidae, Sauria): isolation and impoverishment in small island populations

AbstractThe Aegean wall lizard Podarcis erhardii, is widely distributed across the islands of the Aegean Sea (Greece). While there exists a relatively substantial body of knowledge on the ecology and life history of the species, the parasite communities of the taxon remain almost completely unknown. Quantifying the composition of these communities in P. erhardii is not only important for autoecological reasons, but also because inter-island comparisons of this lizard's parasite communities can shed light on the factors that structure parasite diversity in general. Here we investigate the gastrointestinal parasite communities of P. erhardii populations occurring on 16 landbridge islands of the Sporades group in the NW Aegean Sea by examining the gastrointestinal tracts of 113 lizards. In all, 8 species of helminths were found: 1 Trematode (Paradistomum mutabile), 1 Cestode (Oochoristica sp.) and 6 Nematodes (Parapharyngodon micipsae, Parapharyngodon bulbosus, Parapharyngodon echinatus, Spauligodon sp., Abbreviata sp., and Skrjabinelazia sp.). The prevalence, mean intensity, and mean abundance of infection were respectively 63.71%; 6.01 (±11.71; range 1-90); and 3.57 (±9.5; range 0-90). Brillouin's index of diversity for the Sporades was 0.048 (±0.13; range 0-0.142). These values were lower than for most other mainland and insular lacertid populations, and suggest that the investigated island populations harbor very depauperate helminth communities. The severe impoverishment of the parasite communities and the differential persistence of generalist parasite species with simple life cycles is most likely the result of a combination of insular environmental conditions (spatial and temporal isolation, arid climate, small host population sizes) and host life history characteristics (diet, simple gastrointestinal tract architecture). The paucity of parasites in these relictual island populations suggests that small reptile populations fragmented by anthropogenic activities may not be able to sustain their native parasite communities over the long term.

The consequences of a future eustatic sea-level rise on the deltaic coasts of Inner Thermaikos Gulf (Aegean Sea) and Kyparissiakos Gulf (Ionian Sea), Greece

The spatial consequences of future sea-level rise upon the coastal plains of Greece are examined; in particular, those related to the formation and evolution of the river-deltas. For this reason, the fluvially-dominated deltas of the Axios and Aliakmon rivers of Inner Thermaikos Gulf (NW Aegean Sea) together with the wave-dominated delta of the Alfios River (Kyparissiakos Gulf, Ionian Sea), are investigated. Coastal changes are quantified due to the combined effects of the processes of inundation, because of the increased sea level, and subsequent coastal erosion, due to increased exposure to wave action. Predictions of responses to future sea-level rise, of 0.5 to 1 m, are made. In the case of the deltaic coast of the Alfios, exposed to high waves and protected by dune fields, shoreline retreat of up to 700 m is predicted. The low-lying bird-foot type deltas of the Axios and Aliakmon are expected to retreat by more than 2 km. Furthermore, coastline retreat in the case of Alfios is related primarily to the process of shore zone erosion; in the case of the Axios and Aliakmon, it is related to the process of inundation.

Recent evolution of a Mediterranean deltaic coastal zone: human impacts on the Inner Thermaikos Gulf, NW Aegean Sea

The Inner Thermaikos Gulf is located in the northwestern Aegean Sea, receiving water and sediment fluxes from the Axios, Aliakmon, Gallikos and Loudias Rivers. The geomorphological and sedimentological evolution of the system is reconstructed for the last 150 years (1850–2000), on the basis of detailed analysis of historical bathymetric charts. Late Holocene history is considered within the context of changing riverine sediment supply and human activities. Three evolutionary stages are identified. Stage I (1850–1916) corresponds to a natural phase of rapid deltaic progradation and sea-floor deposition, with an average sediment accumulation rate of 6.5 × 10 6 m 3 a −1 . During Stage II (1916–1956), human interference (e.g. artificial changes in river delta plains, realignment of channels and land reclamation schemes) to the deltaic system increased sediment delivery to the coastal waters by a factor of three; this, in turn, enhanced the progradation of the active river mouth areas. In contrast, Stage III (1956–2000) is characterized by significant coastline (deltaic) retreat and erosion of the adjacent sea floor (net loss of 2.5 × 10 6 m 3 a −1 ); this was as a result of extensive river damming, which trapped a significant part of the sediment moving seaward. Furthermore, these human impacts have affected the character of the surficial sea-bed sediments of the Gulf, by reducing the proportion of mud. The response of the deltaic margin of the Inner Thermaikos Gulf to various anthropogenic interventions seems to be analogous to that of other deltas in the Mediterranean region where large drainage projects, the development of irrigation networks and dam construction have taken place within their river basins.

Distribution of mesozooplankton resting eggs in seabottom sediments of Thermaikos gulf (NW Aegean Sea, Greece) and possible effects of sediment resuspension

The distribution of mesozooplankton resting eggs was studied in the bottom sediments of Thermaikos Gulf (Aegean Sea, Greece), within the framework of the EU project INTERPOL; possible effects of sediment resuspension, due to physical forcing (storm events) and/or to anthropogenic activity (trawling) on the egg assemblages were investigated. Sediment core slices of 2 cm height were collected down to 10 cm depth at 6 stations (from water depth ranging from 25 to 60 m); mesozooplankton samples from the water column were obtained simultaneously. Sampling was performed in September 2001 (before trawling activities and without storm events), in late October 2001 (after the start of the trawling activities) and in February 2002 (after 120 days of intensive trawling activities and the stormy season). The total abundance of eggs was higher at stations located close to the rivers’ mouths, with the muddy sediments of the bed and the water column rich in zooplankters, than at stations located at greater depths and with muddy-sand bed sediments. At the former stations, the vertical distribution of resting eggs has revealed a trend of homogenisation within the sediment column, from September to February; this is related probably to sediment resuspension. At the latter stations, no clear temporal variability in the vertical distribution was detected. The eggs found in the bottom sediments of Thermaikos Gulf were assigned to 16 morpho-types. Amongst these, eggs assigned to Paracartia latisetosa and Labidocera wollastoni (as well as one type called as “Calanoida 3”), were found to be dominant at all the stations and during all the sampling periods, both as full and empty eggs.

234Th: 238U disequilibrium as an indicator of sediment resuspension in Thermaikos Gulf, northwestern Aegean Sea

234Th: 238U disequilibria have been used extensively as tracers of particle dynamics in marine environments. 234Th ( t 1/2=24.1 days) can be used as “proxy” for particle reactive pollutants, due to their similar rapid rate of scavenging onto particles and subsequent removal from the water column, to the sediments. Radioactive disequilibrium can be exploited to determine the rates and time-scales of processes occurring over days to months; in this instance the residence times of dissolved and particulate species with the benthic nepheloid layer (BNL). Three sampling cruises were undertaken in Thermaikos Gulf (NW Aegean Sea) during contrasting periods, to examine the impact of natural and anthropogenic activity on sediment resuspension. September and October 2001 represented background and trawling periods, respectively; January 2002 represented a mixed period, of trawling and storms. Dissolved 234Th is scavenged actively at the BNL, in the presence of suspended particulate material (SPM), with a mean residence time of 16 days. There is a weak inverse correlation between dissolved 234Th residence time and SPM concentration in the BNL, with the shortest residence times occurring during October 2001. No relationship was observed between particulate 234Th activities and SPM concentrations, indicating that particles are rapidly removed from the system, either by sinking or advection. The mean particulate 234Th residence time is 5 days.

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.

Delta progradation and sediment fluxes since the last glacial in the Thermaikos Gulf and the Sporades Basin, NW Aegean Sea, Greece

Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three seismic Units: (i) the uppermost Unit A that represents delta progradation during the last 6000 yr when the sea surface almost reached the present level (Highstand Systems Tract, HST); (ii) Unit B that includes relatively coarse-grained sediments deposited in a shallow, high-energy, estuarine environment during the post-glacial transgression (Transgressive Systems Tract, TST); and (iii) the lowest Unit C which may represent late glacial prodeltaic deposits and slope to basin turbidites (Lowstand Systems Tract, LST). Seismic units A and B overlay a well-defined unconformity which resulted from sub-aerial erosion during the late glacial sea-level fall. Subtracting the thickness of Unit A from the present bathymetry, the paleo-relief of the Late Holocene times (ca. 6000 yr BP, sea level up to − 20 m) was assessed. Similarly, the paleo-relief ∼24 000 yr BP (sea level − 100 to − 120 m) was estimated. The main morphological feature is the incised valley of a major river that resulted from the confluence of the Axios, Aliakmon, Loudias, Gallikos and possibly Pinios Rivers. Sediment fluxes in the NW Aegean Sea were estimated for three time spans of the Late Quaternary (Interval I: 6000 yr BP–present, Interval II: 18 000– 6000 yr BP and Interval III: ∼24 000–18 000 yr BP). The terrestrial sediment load supplied by the Axios, Aliakmon, Pinios, and smaller rivers, was estimated at 35.4 × 10 9 t for Interval I. 93% of this material was deposited on the continental shelf, whereas the remaining 7% was transported to the adjacent basin. The mean annual terrestrial flux was estimated at 5.5 × 10 6 t yr − 1 . During Interval II, more than 79 × 10 9 t of terrestrial sediment were discharged into the area (terrestrial flux 6.6 × 10 6 t yr − 1 ), of which 86% was deposited on the shelf. During Interval III, the terrestrial load was 40.6 × 10 9 t (terrestrial flux 6.8 × 10 6 t yr − 1 ), and sediments were predominantly deposited on the slope and basin. Based on the sediment's carbonate content, the biogenic loads and fluxes were also determined. The biogenic flux during Intervals II and III was found to be ∼2.5-times higher than during Interval I.

Modelling the water mass exchange through navigational channels connecting adjacent coastal basins - application to the Channel of Potidea (North Aegean Sea)

Abstract. The research objective is the detection of the mechanism of the water mass exchange through a navigational channel connecting two adjacent coastal basins. The research involves the application of a mathematical model in parallel to in-situ measurements. The hydrodynamic circulation in the greater area of the NW Aegean Sea is modeled by means of a barotropic circulation model. Wind, Coriolis and Tide are the main forcings taken into account. The flow through the channel is resolved at a subgrid scale by means of a local open channel flow model. The comparison between field measurements, recorded during a limited period, and the model results supports the model verification. The study is integrated by an operational application of the model under various realistic forcings. The results help to gain a better understanding of the mechanisms regulating the water mass exchange and the consequent interaction between two adjacent connected coastal basins. From the case study of the Potidea channel it is revealed that the water mass exchange under mean wind forcing is of the same order as the one induced by the tidal forcing.

Geochemistry and mineralogy of the NW Aegean Sea surface sediments: implications for river runoff and anthropogenic impact

Surface sediments of the NW Aegean Sea were analyzed for clay mineral composition (94 samples), organic C and carbonate content, and major and minor elements (112 samples). Illite is the most abundant clay mineral, followed by smectite, chlorite and kaolinite. Clay minerals are preferentially deposited within the continental shelf and slope environment, due to the prevailing cyclonic circulation and the formation of flocs in the rivers’ pro-delta areas. The spatial distribution of major lithogenic elements (Si, Al, Ti, Fe) is substantially biased by the presence of relict sands located in the central-eastern part of the Thermaikos Gulf continental shelf. Biogenic elements (Ca, Sr) are noticeably pronounced on the northern flank of the North Sporades Islands. Organic C content and minor elements Cu, Zn, As and Pb are enriched markedly over the Thessaloniki Bay and Gulf suggesting substantial human impact, deriving largely from untreated or partly treated domestic and industrial effluents. The terrigenous component of the elements is preferentially contributed from the Axios River (Zn and Pb), the Aliakmon River (Cr, Co, Ni, Cu and As), and to a lesser extent from the Pinios River (V, Co, Ni and Cu); a considerable part of the metals originates in ultra-mafic and volcanic formations, which are abundant in the rivers’ catchment basins. Carbonate content exhibits great variability, with the highest values observed in biogenic sediments of the Sporades Basin. In the latter area, Mn (and Fe) oxides and hydroxides were found as coatings on calcite. The coatings were enriched in Cr, Co, Ni, Zn, As, Mo and Pb, due to adsorption or ion-exchange during early diagenesis. The combined influence of the river systems, the Thessaloniki metropolis, and the diverse sedimentological background, generates great patchiness in the distribution of major and minor elements.

Peracarida populations of hard substrate assemblages in ports of the NW Aegean Sea (eastern Mediterranean)

This study deals with the structure of Peracarida populations in four ports in the NW Aegean Sea, Greece, and with the degree this structure is influenced by the particular biotic and abiotic conditions that prevail in the ports. Quantitative samples were taken during summer and winter in two successive years from artificial hard substrates and were analysed using common biocoenotic methods. The examination of approximately 81,250 specimens revealed the presence of 24 Peracarida species, the most dominant of which were Corophium acutum, Leptochelia savignyi and Elasmopus rapax. All species are very common and have been reported from many sites and assemblages in the N Aegean Sea. The ratios of certain Peracarida genera are discussed as possible indicators of environmental health that may be used in long-term biomonitoring programmes on the impact of pollution in harbours.

Modelling studies on the processes that influence matter transfer on the Gulf of Thermaikos (NW Aegean Sea)

The development and application of a three-dimensional hydrodynamic and sediment transport model for the Gulf of Thermaikos, in the Northwestern Aegean Sea is presented. The processes that control the transfer of river-borne waters and fine-grained sediments are examined. These processes are: the overall basin circulation, the wind-driven flow, the buoyancy-driven flow that is associated with river plume dynamics and the sedimentation processes (flocculation, settling, deposition and erosion). We perform individual experiments, where only some of the processes are included, in order to study the different components of the transport mechanism separately. We also perform comprehensive experiments, where all processes are taken into account. It is found that a large percentage of the suspended particulate matter is deposited on the seabed of the Thermaikos Gulf and mainly near the river discharge sites. Although the sedimentation processes are of primary importance, the transport rates and pathways are greatly affected by the hydrodynamic processes that control circulation. Furthermore, the basin topography has a considerable impact on the transport, as the main rivers discharge near the narrow basin head and near areas of strong coastline curvature that act as sediment trapping zones.

Particulate matter spatial–temporal distribution and associated surface sediment properties: Thermaikos Gulf and Sporades Basin, NW Aegean Sea

Particulate matter (PM) distribution was studied in the NW Aegean Sea (Eastern Mediterranean) over a series of four seasons. PM concentrations in the surface and bottom nepheloid layers exhibit persistent maxima close to the river mouths; the rivers are identified as the major sources of PM. In general, higher particulate matter concentration (PMC) values appear in the shelf of the Thermaikos Gulf, whereas the deep Sporades Basin represents the area of lowest PM concentration. PMC during winter is much higher than in summer. This strong seasonal feature is attributed to the variation of the fresh-water supply, which is maximised during winter and spring, and almost negligible during the dry seasons. PM is mainly transported southwards and preferentially along the western coastline of the study area, due to a well-defined and dominant cyclonic circulation. Lateral transport of the PM prevails, whereas vertical particle transport is relatively limited. BNL formation is mainly attributed to sediment resuspension forced by the near-bottom currents. Surface sediment grain-size distribution is characterised by the presence of relict sands in the central and eastern shelf, while fine-grained muddy sediments cover the western shelf and the Sporades Basin. Relict sands were deposited during the Holocene sea-level rise. The general water mass circulation and the distance from the PM sources seem to favour PM deposition close to the river mouths and along the western coastline, while PM hardly reaches the eastern part of the area. As a result, relict sands remain uncovered or partly mixed with modern fine sediments. The shelf traps most of the PM, while some portion escapes to the deep Basin, probably from the western side of the continental slope.

The contribution of near-bed currents to modern sedimentation processes in the deep waters of the Hellenic Arc-Trench system, eastern Mediterranean

The effects of near-bed current activity on modern sedimentation were examined in various deepwater environments (>500 m) of the Hellenic Arc-Trench system. Near-bed currents were able to resuspend essentially flat beds covered by very fine sediments (>8.5 φ) only when current speeds exceeded 11 cm s–1. At lower speeds, the initiation of resuspension of the muddy sediments was related to increased hydraulic bed roughness resulting from biogenic benthic activity. As such, observed near-bed currents make different contributions to the regional sedimentation processes, i.e., at levels which are low in the Gulf of Corinth, moderate in the NW Aegean Sea and Zakynthos Channel, and high in the NE Ionian Sea.

Distribution of suspended particulate matter determined by in-situ observations and satellite images in the NW Aegean Sea (Greece)

Suspended particulate matter (SPM) patterns in the surface waters of the NW Aegean Sea were studied by (1) determining SPM concentration by water filtration, (2) measuring light transmission, and (3) evaluating satellite images. The SPM signals of the three major rivers discharging into the study area were recorded by all three methods, thereby providing information about the sources, transport pathways, and regional dispersion patterns of the SPM. The filtration of water samples and light transmission measurements were found to be good indicators of SPM concentrations in surface waters. Most of the SPM is composed of terrigenous minerals, thus explaining the correlation between the beam attenuation coefficient and the SPM concentration. A Landsat image obtained for the study period was found to adequately reveal regions with high SPM concentrations. Low concentrations, on the other hand, remain obscured.

Thermaikos Gulf Coastal System, NW Aegean Sea: an overview of water/sediment fluxes in relation to air–land–ocean interactions and human activities

This 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/km 2 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 km 2/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.

Late pleistocene-holocene sedimentation in the NW Aegean Sea: A palaeoclimatic palaeoceanographic reconstruction

Sedimentological (particle-size, organic carbon, calcium carbonate, clay mineralogy and radiocarbon dating) and micropalaeontological investigation of 9 cores from the NW Aegean Sea, eastern Mediterranean, have enabled five main lithological units to be identified. The units cover a period from the Late Pleistocene to the present day. On the basis of these results, and reference to other studies, a palaeo-reconstruction is presented for the area. The reconstruction takes into account the increase in sea level during the period, the decrease in fluvial inputs issuing to the area from the north Mediterranean coastline and the possible influence of water issuing from the Black Sea. It is concluded that the sedimentological and oceanographic regimes of the area were strongly influenced by a fluvial component during the Late Pleistocene and early Holocene, whereas today, the sedimentary record is more indicative of an open oceanic environment.

Sapropelic layers in the NW Aegean Sea

Summary The present study examines sapropelic layers and associated sediments in the NW Aegean Sea, based upon the analysis of cores collected during the 7/78 cruise of the R.R.S. Shackleton . Preliminary sedimentological analyses of some of the cores, including the use of X-ray techniques, did not at first detect either a sapropel or a sapropelic layer (defined as &gt;2% and 0.5 – 2.0% organic carbon, respectively—Sigl et al. 1978) in the sediment. Further investigations, including the analysis of organic carbon, on twelve of these cores have demonstrated the presence of horizons relatively rich in organic carbon. These horizons contain up to approximately 1.0% organic carbon and could be regarded as sapropelic layers. The horizons vary between 26 and 33 cm in thickness and are found at depths of 25 to 100 cm below the sediment-water interface, in cores which range from 101 to 240 cm in length. Organic carbon profiles are presented, together with a discussion of the corresponding X-ray analysis and a preliminary note on the biogenic contributions to these sediments.

Temporal variations in sedimentation patterns: NW Aegean Sea

Cores 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.