The Hellenic deep sea observatory: Science objectives and implementation

The Hellenic observatory in the SE Ionian Sea is located on the steep marginal slopes and basins of the western segment of the Hellenic Arc and Trench System (HATS) (Figure 5.1). The Hellenic Arc and Trench System is a typical subduction zone that is the most tectonically active region in Europe, implying a complicated submarine morphology with numerous, deep, pull-apart sub-basins and a variety of geohazards like high seismicity, slope instabilities and basin wide tsunamis. Fluid emissions, methane gas seeps and mud volcanism in the Eastern Mediterranean accretionary prism provide the substrate for specific deep sea ecosystems. The deep waters of the sub-basins of the western sector of the Hellenic Trench are also sensitive to climate changes, since the deep sub-basins are the ultimate destination of dense (cold and salt) water masses formed in the Adriatic and Aegean Seas. Consequently, the temperature and salinity of bottom waters provides a year-toyear record of the (winter) low temperature and/or precipitation-aridity of the NE Mediterranean Sea. Being the most oligotrophic European sea the deep ecosystem of the Mediterranean Sea is sensitive to climate changes.