Report on work conducted under the sea (2014) and data analysis (2015-2016)
The project’s aim is to map the drowned landscapes of the Inner Ionian Sea Archipelago. Archaeological research conducted on the islands of this inner and protected sea, namely Lefkas, Meganisi, Thilia, Atokos, Arkoudi, by the University of Crete, in collaboration with the Greek Ministry of Culture under the aegis of the Inner Ionian Sea Archipelago Survey brought to light numerous prehistoric sites in caves and the open air. This work on land raised the need to explore the Pleistocene and early Holocene inundated landscapes that lie beneath the sea around the islands (Galanidou 2014; 2015; 2016). This need exists because during low sea-level stands of the Pleistocene many of the islands were joined together and to the mainland. The underwater project is in line with recent developments in human evolution research that embrace marine archaeology (Flemming et al. 2014; Harf et al. 2016; Sakellariou and Galanidou 2016). It has produced new palaeogeographic reconstructions on a key, yet little-investigated, pathway between Africa and Eurasia. The linking thread is the Quaternary Ionian Sea, connecting or separating landscapes, fragmenting and then conjoining them. Τo this end the University of Crete commissioned the Institute of Oceanography of the Hellenic Centre for Marine Research (HCMR) to conduct a marine survey and ground truth work in the Inner Ionian Sea Archipelago.
In summer 2014 two periods of research were completed.
The first period lasted 6 days in June 2014. It was devoted to the systematic, high resolution seismic sub-bottom profiling in areas of the Inner Ionian Sea Archipelago, aiming at defining and mapping submerged low sea-level paleo-shorelines and prehistoric landscapes. This was achieved with the use of a boomer-type sub-bottom profiler and side-scan sonar, prospecting the seafloor to map submerged caves.
HCMR’s research team arrived on Meganisi on June 19th and installed the research equipment on the vessel “SOFIA” (Fig. 1), a very neat, 10m boat made available on site (thanks to the long-term collaboration between the University of Crete and the Municipality of Meganisi and the generosity of the former mayor Stathis Zavitsanos and the vessel owner, captain Panos Konidaris). The next five days (20-24 June) were spent at sea aboard the “SOFIA”. Work started every morning at about 08:00 and ended in late afternoon or early evening (18:00-19:00). During the four-day survey over 80 nautical miles of sub-bottom profiles, side-scan sonar lines and echo-sounder profiles were acquired, at a mean speed of 3 knots.
Preliminary results drawn from the processing and interpretation of the high-resolution seismic data during and after the mission include (Fig. 6):
Mapping of paleo-shorelines at various depths (up to 225 m) below the present sea-level, associated with low sea-level stages (glacial periods) of the last 270,000 thousand years. More precisely, the data obtained support the detailed reconstruction of the shorelines at 20,000 years, 60,000 years, 140,000 and 270,000 years before present, and possibly at even older periods.
- Mapping of so far unknown faults crosscutting the sea-floor and dislocating the submerged paleo-shorelines.
- High resolution mapping of the submerged rocky slopes along the southern shore of Meganisi Island and around Kythros Island.
The second period lasted 5 days in August 2014. It included in situ underwater observation, visual (photo and video) documentation and rock sampling, as well as the collection of underwater imagery for the creation of both ortho-photomosaics and the 3D photogrammetric reconstruction of selected locations of potential interest. All work was conducted with SCUBA, at a depth range of 0-20 m, by two experienced HCMR scientific divers. A Nikon D200 camera with wide-angle lens inside a Subal aluminum housing, coupled with two Inon underwater strobes was used for the underwater photography, while a GoPro Hero3+ was used for the underwater videos.
On day 1 reconnaissance diving and visual documentation of the shallow rocky sea bottom (Fig. 7 & 8) at selected parts of the Kythros Island took place. The subsequent days were dedicated to an underwater photogrammetric survey that consisted of marking and geo-referencing control points on the sea-bottom (Fig. 9) and the collection of 1,334 underwater photos (Fig. 10) with adequate image overlap for a high-resolution 3D reconstruction of a rocky bottom scene with a surface of about 390 m2 at depths ranging 0-5 m, in close vicinity to the coast.
Due to the fact that the areas of interest were in very shallow waters, work on these days was conducted between 07.00 and 10.30 each morning, to avoid the sunlight’s caustic effects created by the waves. Such cause difficulties in the automatic analysis and processing of the underwater photos based on Structure from Motion (SfM) algorithms. The analysis has produced highly detailed ortho-photomosaics of the northern part of Kythros Island, while the final 3D photogrammetric reconstructions are expected soon.
HCMR’s research team in the Ionian Sea was coordinated by Dr D. Sakellariou and included Dr G. Rousakis, P. Georgiou (marine geologists-geophysicists), I. Pampides (engineer), Y. Issaris (marine ecologist, underwater imaging/photogrammetry), Dr. M. Salomidi (marine ecologist, scientific diving officer) and A. Zavitsanou (MSc in marine geology student).
In the ensuing years, 2015-2016, detailed processing and interpretation of the marine geological-geophysical data and the thorough reconstruction of the submerged shorelines and landscapes were undertaken. They also formed the subject of an MSc Thesis of a student who joined HCMR’s team during the fieldwork. This thesis was defended successfully last month (Zavitsanou 2016). Part of this research was presented before an international conference in Mytilene (Zavitsanou et al. 2015) https://www.researchgate.net/publication/281345855_Paleogeographic_reconstructio n_of_the_Inner_Ionian_Sea_during_Late_Pleistocene_low_sealevel_stands_Prelimin ary_results https://www.academia.edu/19887376/Paleogeographic_reconstruction_of_the_Inner_ Ionian_Sea_during_Late_Pleistocene_low_sealevel_stands_Preliminary_results
Two more publications are currently being prepared.
Flemming, N. C., M. N. Çağatay, F. L. Chiocci, N. Galanidou, G. Lericolais, T. Missiaen, F. Moore, A. Rosentau, D. Sakellariou, B. Skar, A. Stevenson, and H. Weerts. 2014. Land Beneath the Waves: Submerged Landscapes and Sea Level Change. A Joint Geosciences-humanities Strategy for European Continental Shelf Prehistoric Research, edited by N. C. Chu, and N. McDonough. Ostend: Position Paper 21 of the European Marine Board.
Galanidou, N. 2014. “Archaeological Survey on the Inner Ionian Sea Archipelago.” Encyclopaedia of Global Archaeology, edited by C. Smith. New York: Springer, 3882–8.
Galanidou, N. 2015. “Seascape Survey on the Inner Ionian Sea Archipelago”. Field Archaeology from Around the World. Ideas and Approaches, edited by M. Carver, B. Gaydarska, and S. Mondon-Subias. New York: Springer, 101–6.
Galanidou, N. 2016. “Before ancient Nericos, what? Palaeolithic finds from Karyotes Lefkas”. Nericos, Lefkas, Kastro the Longest-lived Capital of Lefkas, Conference Proceedings August 2010, edited by C. Papadatou-Giannopoulou. Lefkas: Cultural Centre, 83-111 (in Greek).
Harff J., G. Bailey and F. Luth, 2016. Geology and Archaeology: Submerged Landscapes of the Continental Shelf. Geological Society, London, Special Publications, 411.
Sakellariou, D. and N. Galanidou, 2016 “Pleistocene submerged landscapes and Palaeolithic archaeology in the tectonically active Aegean region”. Geology and Archaeology: Submerged Landscapes of the Continental Shelf, edited by J. Harff, G. Bailey and F. Luth. Geological Society, London, Special Publications, 411, 145-178. First published online July 6, 2015, http://dx.doi.org/10.1144/SP411.9
Zavitsanou, A. 2016. Paleogeographical Reconstruction of the Northern Inner Ionian Sea Archipelago during Late Quaternary Low Sea Level Periods. M.Sc. Thesis, Department of Geophysics-Geothermics, University of Athens.
Zavitsanou, A., D. Sakellariou, G. Rousakis, P. Georgiou, and N. Galanidou. 2015 “Paleogeographic Reconstruction of the Inner Ionian Sea during Late Pleistocene Low Sealevel Stands: Preliminary Results”. Paper presented in the 11th Panhellenic Symposium on Oceanography and Fisheries, Mytilene, Lesvos Island, Greece, 997–1000.