Why Are Scientists Searching for Undiscovered Shipwrecks and Unusual Geological Features in the Aegean Sea?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on earth, cures for human diseases, answers to how to achieve sustainable use of resources, links to our maritime history, and information to help protect endangered species. In addition, exploration of active volcanoes and other geological features of the deep sea provides important information on potential hazards such as risks to shipping from shallow eruptions, as well as the generation of dangerous tsunamis from large submarine eruptions and landslides.
Mariners have traveled the Aegean Sea since Neolithic times (the ‘Stone Age’; 6,500 - 3,200 BC). Motives for their voyages ranged from trading to exploration to warfare, making seafaring prominent in the history of cultures that include the Minoans (ca 2,600 - 1,450 BC), Mycenaeans (ca 1,600 - 1,100 BC), Ancient Greeks (776 - 323 BC), and Hellenistic Greeks (323 - 146 BC). Remnants of ancient ocean voyages (i.e., shipwrecks) can provide information about trading patterns, sociopolitical networks, technological development and many other unique insights into these cultures; but a variety of factors make it difficult to find such remnants. One problem is that interactions between cultures were not always peaceful; and destroying important shipping assets would have been an obvious step toward conquering an opponent.
Another obstacle is the same feature that makes ancient shipwrecks so valuable - their age. In addition to increasing the severity of deterioration by biological and chemical processes, the passage of time also increases the likelihood that ancient shipwrecks will be impacted by natural disasters. The southern Aegean region has experienced numerous severe volcanic events and tsunamis, including the eruption of a volcano near a small island called Thera (also known as Santorini), sometime between 1,650 and 1,450 BC. This eruption is estimated to have been four times more powerful than the Krakatoa volcano of 1883, left a crater 18 miles in diameter, spewed volcanic ash throughout the Eastern Mediterranean, and may have resulted in global climatic impacts. Coupled with earthquakes and a tsunami, the volcano destroyed human settlements, fleets of ships, and may have contributed to the collapse of the Minoan civilization.
Even if ancient shipwrecks survive natural disasters (and those caused by humans), finding, exploring and scientifically studying these sites are complicated by the fact that much of the Aegean Sea is relatively deep. Total darkness and an environment that is extremely hostile to humans have, until recently, been obstacles that are virtually insurmountable. Technological advances over the past decade, though, have made deep-water archaeology a much more feasible endeavor. The PHAEDRA 2006 Expedition will use the SeaBED Autonomous Underwater Vehicle to search for deepwater shipwrecks, as well as conduct precise geological and chemical surveys in the vicinity of underwater volcanoes in the Aegean Sea. Autonomous Underwater Vehicles (AUV) are self-contained underwater robots that operate without a physical cable or tether such as those used on remotely operated vehicles (ROVs). SeaBED is designed specifically to provide precise maps and high-resolution three-dimensional color images of seafloor features, as well as to carry equipment for measuring physical and chemical properties of the surrounding seawater. Using SeaBED to map and document survey sites frees archaeologists from tedious measuring and sketching tasks, and allows them to concentrate on interpreting survey results. For more information about SeaBED, visit:
This expedition is an unusual collaboration between four U.S. research institutions and the Greek Ephorate of Underwater Antiquities (Hellenic Ministry of Culture) and Hellenic Centre for Marine Research. At the direction of the Ephorate of Underwater Antiquities, scientists from Woods Hole Oceanographic Institution, Massachusetts Institute of Technology, Franklin W. Olin College of Engineering, and Johns Hopkins University will work with their Greek counterparts to use underwater robots to make detailed archaeological surveys of shipwrecks in deep water. The science team will also will investigate the Columbo submarine volcano off the island of Santorini. Columbo is an active volcano, notorious for its explosive eruption in September 1650 A.D., which released ash, pumice fall and toxic gases. To learn more about volcanic processes in this area, surveys will precisely map the seafloor and gather chemical data that will provide clues about volcanic activity as well as unusual geological features such as cold seeps and volcanic vents..
The PHAEDRA 2006 Expedition is focused on using modern oceanographic tools and techniques to search unexplored regions of the Aegean Sea for clues to the location of ancient shipwrecks and active geological features. Key questions concern technology, archaeology, and geology. The basic technological question is: How can an autonomous underwater vehicle be used to collect archaeological, chemical, and geological data to find or predict the locations of undiscovered archaeological sites (primarily ancient shipwrecks) and unusual geological activity? The archaeological questions directed toward these sites include: what do these sites reveal about the organization and nature of ancient maritime trade and communication; and how have these activities matured through time? Geological questions include: what hydrothermal, cold-seep, and/or volcanic activity is occurring in unexplored areas, and what may such activity reveal about future seismic events in the Aegean region?
More About Volcanoes
According to the theory of plate tectonics, the Earth’s crust consists of large segments known as tectonic plates. These plates are portions of the outer crust (lithosphere) about 5 km thick, as well as the upper 60 - 75 km of the underlying mantle. Tectonic plates move on a hot flowing mantle layer called the asthenosphere, which is several hundred kilometers thick. Heat within the asthenosphere creates convection currents (similar to the currents that can be seen if food coloring is added to a heated container of water) that cause the tectonic plates to move several centimeters per year relative to each other.
The junction of two tectonic plates is known as a plate boundary. Where two plates slide horizontally past each other, the junction is known as a transform plate boundary. Movement of the plates causes huge stresses that break portions of the rock and produce earthquakes. Places where these breaks occur are called faults. A well-known example of a transform plate boundary is the San Andreas Fault in California.
Where tectonic plates are moving apart, they form a divergent plate boundary. At these boundaries, magma (molten rock) rises from deep within the Earth and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater (Iceland is an exception), and form submarine mountain ranges called oceanic spreading ridges.
If two tectonic plates collide more or less head-on, they produce a convergent plate boundary. Usually, one of the converging plates moves beneath the other in a process called subduction. Subduction produces deep trenches, and earthquakes are common. As the sinking plate moves deeper into the mantle, increasing pressure and heat release fluids from the rock causing the overlying mantle to partially melt. The new magma rises and may erupt violently to form volcanoes that often form arcs of islands along the convergent boundary. These island arcs are always landward of the neighboring trenches. This process can be visualized as a huge conveyor belt on which new crust is formed at the oceanic spreading ridges and older crust is recycled to the lower mantle at the convergent plate boundaries.
The tectonic setting of the Aegean/Mediterranean Sea area is complex, and includes two major plates (the Eurasian and African Plates) as well as several minor ones. The South Aegean (or Hellenic) Volcanic Arc extends from the mainland of Greece through the islands of Aegina, Methana, Poros, Milos, Santorini (also called Thera), Kos, Yali, Nisyros, and the Bodrum peninsula of Turkey. Earthquakes at depths of 150 - 170 km are caused by the subduction of the African Plate beneath the Eurasian Plate, which also forms the Ionian, Pliny, and Strabo deep-sea trenches south of Crete.
The Columbo (Kolumbo) volcano is part of the Santorini volcanic field that also includes the islands of Santorini (Thera) about 7 km to the southeast and the Christiana islands about 30 km to the southwest. Most of the known eruption centers occur on the Kameni tectonic line, which intersects the Christiana Islands, the Akrotiri peninsula, and the islands of Palea and Nea Kameni. The parallel Columbo tectonic line passes through the centers of Megalo Vouno and the Columbo volcano. There have been many eruptions in the Santorini volcanic field during the past 4,000 years, including the notorious Minoan (ca. 1640 BC) and Columbo (September 27, 1650) eruptions, which were accompanied by strong tsunamis. Improved technology for predicting these kinds of catastrophic events is extremely important; because geologists have no doubt that these volcanoes will erupt again.
More About Cold Seeps
Cold seeps are areas in which hydrocarbon gases (often methane and hydrogen sulfide) and oil seep out of sediments. These areas are commonly found along continental margins, and (like hydrothermal vents) are home to many species of organisms that have not been found anywhere else on Earth. Typical features of communities that have been studied so far include mounds of frozen crystals of methane and water called methane hydrate ice, that are home to polychaete worms. Brine pools, containing water four times saltier than normal seawater, have also been found. Researchers often find dead fish floating in the brine pool, apparently killed by the high salinity.
Where hydrogen sulfide is present, large tubeworms (phylum Annelida) known as vestimentiferans are often found, sometimes growing in clusters of millions of individuals. These unusual animals do not have a mouth, stomach, or gut. Instead, they have a large organ called a trophosome that contains chemosynthetic bacteria. Vestimentiferans have tentacles that extend into the water. The tentacles are bright red due to the presence of hemoglobin, which can absorb hydrogen sulfide and oxygen, which are transported to the bacteria in the trophosome. The bacteria produce organic molecules that provide nutrition to the tubeworm. A similar symbiotic relationship is found in clams and mussels that have chemosynthetic bacteria living in their gills. Bacteria are also found living independently from other organisms in large bacterial mats. A variety of other organisms are also found in cold seep communities, and probably use tubeworms, mussels, and bacterial mats as sources of food. These include snails, eels, sea stars, crabs, lobsters, isopods, sea cucumbers, and fishes. Specific relationships between these organisms have not been well studied.
Deepwater chemosynthetic communities are fundamentally different from other biological systems, and there are many unanswered questions about the individual species and interactions between species found in these communities. These species include some of the most primitive living organisms (Archaea) that some scientists believe may have been the first life forms on Earth. Many species are new to science, and may prove to be important sources of unique drugs for the treatment of human diseases. Because their potential importance is not yet known, it is critical to protect these systems from adverse impacts caused by human activities (for more information about cold seeps, visit http://www.bio.psu.edu/cold_seeps).
One of the PHAEDRA 2006 Expedition’s key technological components is the SeaBED Autonomous Underwater Vehicle. SeaBED is constructed of two torpedo-like body sections attached by two vertical structural members, and was designed to carry out photographic, side-scan sonar, and bathymetric surveys at depths to 2000 m. Onboard navigation instruments provide measurements of velocity over the bottom, heading, altitude, pitch, roll, integrated position, and depth. The AUV is capable of speeds of 0.3 m/s - 1 m/s, but is normally programmed to run at minimum speed at a fixed distance from the bottom to avoid collisions in case the topography of the bottom suddenly changes. SeaBED’s design makes the AUV extremely stable, so it is capable of operating very near the sea floor, and can independently follow slopes greater than 45 degrees. For more information about SeaBED, visit: