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1.
E. Krasakopoulou E. Souvermezoglou A. Pavlidou H. Kontoyiannis 《Progress in Oceanography》1999,44(4):1460
The Straits of the Cretan Arc are the gateways through which water exchanges between the Cretan Sea and the SE Ionian and NW Levantine Seas. Dissolved oxygen and nutrient fluxes have been quantified for the major straits — Antikithira, Kassos and Karpathos — by combining chemical bottle-sample data and current measurements obtained during the PELAGOS Project during 1994–1995. Two water masses, Cretan Deep Water (CDW) and Transitional Mediterranean Water (TMW) dominate the circulation through the straits and lead to a vertical redistribution of nutrients in the Eastern Mediterranean Sea.The transport of chemicals through the major straits of the Cretan Arc appears to be highly variable. In the Antikithira and Kassos Straits, a net export of oxygen and nutrients from the Cretan Sea towards the open waters of the Eastern Mediterranean was observed throughout the entire study period. In contrast, a net inflow of oxygen and nutrients of Levantine origin was taking place through the Karpathos Strait. It is concluded that the export of nutrients through the Antikithira and Kassos Straits are almost completely balanced by the net import through the Karpathos Strait. 相似文献
2.
In 1998–1999, beam attenuation coefficient (bac) profiles, suspended particulate matter (SPM) and particulate organic carbon (POC) concentrations were assessed during five
cruises in the Saronikos Gulf, eastern Mediterranean, Greece. SPM and POC concentrations (0.05–1.84 mg l−1 and 10.2–468.6 μg l−1, respectively) exhibited strong spatial and temporal variations, related to the different environmental characteristics of
various sectors of the gulf, including wind regime and biological productivity. The Elefsis and Keratsini bays, as well as
the area around Psyttaleia Island, showed the highest POC concentrations. The vertical distribution of POC at stations in
the western basin, as well as in the inner and outer Saronikos Gulf is characterised by higher POC concentrations in surface
waters, associated with higher biological activity. The wastewater treatment plant effluents discharged south of the Psyttaleia
Island are a major source of organic particles which directly influence the intermediate water layers, at least during the
stratification period. Assessments of relationships between bac and SPM or POC concentrations revealed a relatively strong correlation between bac and POC. An equation converting bac readings to POC concentration was established which can be applied to historical and/or future bac measurements, independently of season. POC concentrations estimated from calibrated continuous transmissometer readings were
used to estimate the standing stock of POC in the Saronikos Gulf, which varied between 6,110×106 and 13,450×106 g C during the period June 1998 to February 1999. 相似文献
3.
Evangelia Krasakopoulou Spyridon Rapsomanikis Anastasios Papadopoulos Evangelos Papathanassiou 《Continental Shelf Research》2009,29(11-12):1477-1488
Data on the distribution of fCO2 were obtained during a cruise in the Aegean Sea during February 2006. The fCO2 of surface water (fCO2sw) was lower than the atmospheric fCO2 (fCO2atm) throughout the area surveyed and ΔfCO2 values varied from ?34 to ?61 μatm. The observed under-saturation suggests that surface waters in the Aegean represent a sink for atmospheric CO2 during the winter of 2006. Higher fCO2sw values were recorded in the ‘less warm’ and ‘less saline’ shallow northernmost part of the Aegean Sea implying that the lower seawater temperature and salinity in this area play a crucial role in the spatial distribution of fCO2sw.A first estimate of the magnitude of the air–sea CO2 exchange and the potential role of the Aegean Sea in the transfer of atmospheric CO2 was also obtained. The air–sea CO2 fluxes calculated using different gas transfer formulations showed that during February 2006, the Aegean Sea absorbs atmospheric CO2 at a rate ranging from ?6.2 to ?11.8 mmol m?2 d?1 with the shipboard recorded wind speeds and at almost half rate (?3.5 to ?5.5 mmol m?2 d?1) with the monthly mean model-derived wind speed. Compared to recent observations from other temperate continental shelves during winter period, the Aegean Sea acts as a moderate to rather strong sink for atmospheric CO2.Further investigations, including intensive spatial and temporal high-resolution observations, are necessary to elucidate the role of the Aegean Sea in the process of transfer of atmospheric CO2 into the deep horizons of the Eastern Mediterranean. 相似文献
4.
Marios Apostolou George Gazetas Evangelia Garini 《Soil Dynamics and Earthquake Engineering》2007,27(7):642-654
The rocking of rigid structures uplifting from their support under strong earthquake shaking is investigated. The structure is resting on the surface of either a rigid base or a linearly elastic continuum. A large-displacement approach is adopted to extract the governing equations of motion allowing for a rigorous calculation of the nonlinear response even under near-overturning conditions. Directivity-affected near-fault ground motions, idealized as Ricker wavelets or trigonometric pulses, are used as excitation. The conditions under which uplifting leads to large angles of rotation and eventually to overturning are investigated. A profoundly nonlinear rocking behavior is revealed for both rigid and elastic soil conditions. This geometrically nonlinear response is further amplified by unfavorable sequences of long-duration pulses in the excitation. Moreover, through the overturning response of a toppled tombstone, it is concluded that the practice of estimating ground accelerations from overturning observations is rather misleading and meaningless. 相似文献
5.
S. Zervoudaki C. Frangoulis C. Svensen E. D. Christou E. Tragou E. G. Arashkevich T. N. Ratkova Ι. Varkitzi E. Krasakopoulou K. Pagou 《Estuaries and Coasts》2014,37(4):911-924
This work focuses on the direct measurement of the vertical flux of appendicularian houses in order to assess their importance as a component of vertical carbon flux in coastal areas. For this purpose, arrays of cylindrical sediment traps were deployed for 5 to 8 days at two depths in a coastal area of the northern Aegean Sea (inner Thermaikos Gulf) during spring. The data support the contention that resuspension was minimal. Fecal pellet (FP) production and grazing experiments with the dominant copepods (Acartia clausi) were conducted to provide additional information on the potential FP contribution to the total carbon flux. The magnitude of the vertical flux of particulate organic carbon (POC) ranged between 310 and 724 mg C m?2 day?1. The proportion of phytoplankton carbon in the POC vertical flux was up to 45 %. The contribution of zooplankton FPs to the total carbon never exceeded 5 %. On the contrary, appendicularian houses were an essential component of the biogenic carbon flux contributing up to 55.3 % of the total vertical carbon flux. Consequently, both phytoplankton and appendicularian houses contributed equally to the biogenic carbon flux exceeding 80 % of the total sinking POC. Taking into account the sinking speed of the particles and the environment in the area, all this carbon probably reaches the seafloor, thus indicating a strong pelagic–benthic coupling. 相似文献
6.
Geochemistry of surface sediments and heavy metal contamination assessment: Messolonghi lagoon complex,Greece 总被引：2，自引：2，他引：0
Aristomenis P. Karageorgis Andreas Sioulas Evangelia Krasakopoulou Christos L. Anagnostou George A. Hatiris Harikleia Kyriakidou Konstantinos Vasilopoulos 《Environmental Earth Sciences》2012,65(6):1619-1629
The Messolonghi lagoon complex in Western Greece receives agricultural and domestic effluents both from point and diffused
sources. Surface sediments were analyzed for grain size, organic carbon, total nitrogen, total sulfur, major and minor elements,
aiming at the identification of geochemical relationships between all variables. Enrichment factors and the modified degree
of contamination methods were applied to assess potential heavy metal enrichment related to human activities. Sediment texture
was highly variable, with muddy sediments prevailing. In the central sector of the Messolonghi lagoon, organic carbon contents
were high. Principal factor analysis revealed the following main groups of variables with common geochemical behavior: (1)
terrigenous aluminosilicates (2) organic matter, (3) biogenic carbonates, (4) mineral quartz-aluminosilicates, and (5) Mn-oxides.
Enrichment factors estimated for V, Cr, Mn, Co, Ni, Cu, Zn, and Pb using local pre-industrial sediment showed that all metals
exhibit almost natural background levels, except for Pb, which was found to be slightly elevated (legacy of leaded fuel).
Estimation of contamination factors concluded in similar results, whereas the overall modified degree of contamination was
at the lowest level, therefore suggesting that this transitional water body has not been affected by anthropogenic activities.
The data set may be considered as a baseline for future monitoring projects according to EU policy. 相似文献
7.
Evaluation of seismic hazard for the assessment of historical elements at risk: description of input and selection of intensity measures 总被引：1，自引：1，他引：0
8.
Parveen Sihag Vijay P. Singh Anastasia Angelaki Vinod Kumar Alireza Sepahvand Evangelia Golia 《水文科学杂志》2013,58(13):1647-1658
ABSTRACTInfiltration plays a fundamental role in streamflow, groundwater recharge, subsurface flow, and surface and subsurface water quality and quantity. In this study, adaptive neuro-fuzzy inference system (ANFIS), support vector machine (SVM) and random forest (RF) models were used to determine cumulative infiltration and infiltration rate in arid areas in Iran. The input data were sand, clay, silt, density of soil and soil moisture, while the output data were cumulative infiltration and infiltration rate, the latter measured using a double-ring infiltrometer at 16 locations. The results show that SVM with radial basis kernel function better estimated cumulative infiltration (RMSE = 0.2791 cm) compared to the other models. Also, SVM with M4 radial basis kernel function better estimated the infiltration rate (RMSE = 0.0633 cm/h) than the ANFIS and RF models. Thus, SVM was found to be the most suitable model for modelling infiltration in the study area. 相似文献
9.
Ekaterini Souvermezoglou Evangelia Krasakopoulou Alexandra Pavlidou 《Progress in Oceanography》1999,44(4):67
Nutrient and oxygen data collected in the southern Aegean Sea (Cretan Sea) and the straits of the Cretan Arc, during the four seasonal PELAGOS cruises in 1994–1995, are investigated and compared with data collected from 1987 to 1992 within the same area. During the cruises of the PELAGOS Project, nutrient enrichment of the intermediate layers of the Cretan Sea was observed, as a result of intrusion of ‘nutrient-rich, oxygen-poor’ Transition Mediterranean Water (TMW) compensating the Cretan Deep Water (CDW) outflow. TMW occupied the intermediate layers of the entire Cretan Sea. The concentrations of nutrients within this layer were often two times higher than those observed in the same area during previous studies undertaken before 1992 (increase 2.5 μmol/l of nitrate, 0.05 μmol/l of phosphate and 2.5μmol/l of silicate). The decrease of oxygen in this layer is about 0.8ml/l (35 μmol/l). Outflow of CDW occurs principally through the Antikithira and Kassos Straits (the two deeper straits of the Cretan Arc); it results in an increase of oxygen content but a decrease in the nutrient content of water in the deep and bottom layers outside the Cretan Sea. The major mesoscale features in the area have a major influence of the distributions and exchanges of nutrients and oxygen through the straits of the Cretan Arc. The surface and the intermediate layers were richer in nutrients and poorer in oxygen in spring (March 1994), than in autumn (September 1994). 相似文献
10.
