Managing oceanographic data collated from on-line Information Systems

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Circulation in the Cretan Sea and adjacent regions in late winter 1994

This paper presents the qualitative circulation patterns of the ''upper'' and ''deeper'' layers in the Cretan Sea and its environs in late winter 1994. The qualitative aspects of the flow field were determined primarily by the distribution of salinity on appropriate neutral surfaces and were supported by dynamic inferences. Water circulation presented a complex pattern, characterized by various sub-basin and mesoscale cylonic and anticyclonic gyres and smaller-scale eddies. An interesting finding was the presence of an eastward current meandering north of Crete, in the South Aegean Sea. Another interesting finding was the spreading in the opposite direction - westward - of the high-salinity Cretan Deep Water. The latter appeared to follow broadly the bottom bathymetric contours in its westward spreading from the presumed area of its formation in the deepest part of the Cretan Sea, where it also attained maximum thickness. The water exchanges between the Aegean Sea and the eastern Mediterranean Sea were influenced by their bottom topography and were also affected by the existence of permanent and/or recurrent circulation features and their variability

Hydrological structure of the Cretan Sea and adjacent regions in late winter 1994

Analysis of CTD data collected in the Cretan Sea and adjacent regions in late winter 1994 revealed the hydrological structure of their waters: Modified Atlantic Water (MAW) occurs in the south-eastern Ionian Sea and enters the Cretan Sea through the Antikithira Strait. Levantine Surface Water (LSW) spreads into the Cretan Sea across the Karpathos and Rhodos Straits. Surface waters of Black Sea origin (BSW) are identified in the north-western Cretan Sea. Levantine Intermediate Water (LIW) is present everywhere as a subsurface salinity maximum. Saline and warm Cretan Deep Water (CDW) occurs as a thick bottom layer in the Cretan Sea and also in the Antikithira and Kassos Straits; however, its influence is felt over the entire study area. Notable is the absence of the Eastern Mediterranean Deep Water (EMDW); instead, Eastern Mediterranean Transition Waters (EMTW) occupy thick layers beyond the Cretan Sea, whilst after intruding the latter, via the Antikithira, Kassos and Karpathos Straits, their signature is a pronounced salinity and temperature minimum layer. © 1997 Osservatorio Geofisico Sperimentale

Assessing the trophic status of Lake Mikri Prespa, Greece

Lake Mikri Prespa is a shallow water basin characterized by unstable thermal stratification, primary dimictic conditions and clinograde distribution of dissolved oxygen. The nutrient concentrations are high, indicating a trend towards eutrophication. Total phosphorus input calculated on the basis of the export coefficient accounting for land-uses and other sources is estimated to be of the order of 15 × 106 kg yr-1. A mathematical model is applied to assess the trophic status of Lake Mikri Prespa in the light of development projects recently undertaken in its catchment area. Evaluation of the trophic status reveals that the critical and permissible loading for Lake Mikri Prespa are 0.07 and 0.03 gm-2y-1, respectively. Present loading of the lake is estimated at 0.27 gm-2y-1 indicating that the lake is already at a dangerous level. On the basis of the employed O.E.C.D. relationships, Lake Mikri Prespa is presently classified as mesotrophic to eutrophic

Internal waves revealed by Synthetic Aperture Radar (SAR) imagery in the vicinity of the eastern Cretan Arc Straits (Eastern Mediterranean)

Internal waves have been detected on ERS-1 SAR images obtained during late summer over the eastern Cretan Straits, an area characterised by complex regional physiography, bottom topography, flow regime and stratification patterns of the upper part of the water column. Analysis of the imaged characteristics of the internal waves has revealed a strong diversity in form, propagation direction and type of sea surface modulation, which indicates various mechanisms of generation. Analysis of the currents recorded over the area shows that, although semi-diurnal tidal currents are present, these are of low magnitude in comparison with the overall flow and, therefore, tidal forcing is unlikely to be a major process in the generation of the imaged internal waves. In addition, a well-defined front has been identified within the Rhodes Strait. This front is considered to be the surficial manifestation of the Asia Minor Current, which is a strong and persistent large-scale circulation feature of the Eastern Mediterranean

Tentative study of flow patterns in the North Aegean Sea using NOAA-AVHRR images and 2D model simulation

A statistical technique for image processing, the maximum cross correlation (MCC) method, was utilized on sequences of NOAA-AVHRR thermal data in order to explore the surface advective current dynamics at the discharge region of the Hellespont in the North Aegean Sea. A 2D numerical flow model was also used in order to simulate the barotropic flow pattern of the surface water layer. The model was forced with diurnal wind fields obtained for the same period as the satellite infrared images. The currents (magnitude and direction) derived from the two methods compare satisfactorily despite the fact that some model simplifications were made

Tentative study of flow patterns in the North Aegean Sea using NOAA-AVHRR images and 2D model simulation

A statistical technique for image processing, the maximum cross correlation (MCC) method, was utilized on sequences of NOAA-AVHRR thermal data in order to explore the surface advective current dynamics at the discharge region of the Hellespont in the North Aegean Sea. A 2D numerical flow model was also used in order to simulate the barotropic flow pattern of the surface water layer. The model was forced with diurnal wind fields obtained for the same period as the satellite infrared images. The currents (magnitude and direction) derived from the two methods compare satisfactorily despite the fact that some model simplifications were made