Exploring the Greek Seas

The sea-floor of the Hellenic Seas is characterised by a complex morphology as a result of the geologic history of the eastern Mediterranean and the recent geodynamic processes and movements. The Aegean Sea, between continental Hellas and Asia Minor, has been formed as a back-arc basin behind the southwards migrating orogenic arc and hosts the active volcanic arc. The southernmost Aegean islands (Kythira, Kriti, Karpathos, Rodos) form the southern limit of the Aegean Sea towards the eastern Mediterranean and the Ionian Sea (Figure I.4). The Ionian Sea, located west of continental Hellas and the Hellenic Trench, which surrounds the southernmost Hellenic territories in the south, host the deepest basins of the Mediterranean Sea. Their sea floor relief is strongly controlled by active faulting and is thus very irregular. Most of the gulfs, which dissect the coastline of the Aegean and the Ionian seas are also of tectonic originThe morphology of the surface of the Earth is the result of two main categories of geological processes: the so-called endogenic processes that take place within the Earth’s crust, e.g. motion of lithospheric plates, faulting, volcanism, that create new relief; and the so-called exogenic processes that on the Earth’s surface, e.g. erosion, sediment deposition etc., and tend to modify (smooth out or enhance) the result of the previous ones.

The Aegean Sea has been formed between the Greek mainland and western Turkey, as a result of stretching and extension of the upper crust above the   down-going East Mediterranean plate. Numerous active, offshore faults create a puzzle of tectonic blocks that subside and form deep basins (maximum depths in the Aegean Sea reach roughly 2,500 m) or uplift and remain as islands above the sea level forming the Aegean Archipelago. The islandic and submarine volcanoes of the South Aegean Volcanic Arc (e.g. Milos, Santorini, Kolumbo, Nisyros etc.) are the result of the melting of the subducting plate beneath. The magma (=melted rocks) rises through crustal scale faults to form the active volcanoes on the Earth’s surface.

The Hellenic Arc, from Peloponnese over Crete and Karpathos to Rhodes, marks the southern boundary of the Aegean Sea. It is surrounded to the South by the so-called Hellenic Trench, a major, composite geomorphological feature that was considered previously as the boundary between the subducting east Mediterranean oceanic crust and the overriding Aegean continental crust. The western part, the Ionian Trench, strikes NW-SE, roughly from Zakynthos to south of Gavdos Island, constitutes a succession of deep, elongate, small basins including the Oinousses Deep, the deepest basin in the Mediterranean with 5,200 m depth. The eastern part of the Hellenic Trench is marked by two linear, SW-NE striking troughs, the Pliny and Strabo Troughs or Trenches that have developed along major submarine, crustal scale faults. The troughs terminate north-eastwards into the 4 000 m deep Rodos Basin.

The processes that have led to the creation of the Hellenic Trench are not really well understood yet. Despite that, the Hellenic Trench outlines the northern boundary of the East Mediterranean Ridge. It is a roughly 1,200 km long, arcuate, submarine mountain range that has been formed due to the compression and folding of the >10 km thick sedimentary sequence deposited in the Mediterranean during the Mesozoic and Cenozoic Eras.

In the last 50 years or even more, numerous marine geological and geophysical cruises and surveys have led to a significant improvement of our understanding of the geodynamic, geological and sedimentary evolution and processes that led to the formation of the Aegean Sea in the recent geological period. However, despite the large research effort, a large part of the seafloor of the Aegean Sea remains unexplored or insufficiently surveyed.

The following map visualizes the updated bathymetry of the Mediterranean and Black Seas that has been compiled in the framework of EMODNET Bathymetry project (https://emodnet-bathymetry.eu) by reprocessing at 100 m grid the available, high resolution swath bathymetry data, the low resolution GEBCO bathymetry and the available single beam data. The map highlights with different colors the depth classes in 200 m steps.

Habitat mapping and improved knowledge of these deep-­sea topography features at different spatial scales is still in its infancy. Nonetheless, gathering and updating this knowledge will facilitate a better understanding of the relevance of these structures in sustaining deep-­sea biodiversity as well as provide new insights for defining areas for presentation of deep-­sea biodiversity and ecosystem functioning.

Seafloor exploration has led to the identification of major and quite typical landforms that spread across the Mediterranean and Black seas. Whether it is an extensive shelf, shallow, deep or extremely deep (abyssal) basins, seamounts or canyons, all these massive landforms contribute to the complexity of the sea bottom.

Have a look at some of the most impressive geomorphological features the East Mediterranean Sea has to offer

Follow the link below and take a graphic 3D tour into the East Mediterranean Sea