Chapter 15
Late Pleistocene Environmental Factors of the Aegean Region (Aegean Sea Including the Hellenic Arc) and the Identification of Potential Areas for Seabed Prehistoric Sites and Landscapes

Dimitris Sakellariou,1 Vasilis Lykousis,1 Maria Geraga,2 Grigoris Rousakis1 and Takvor Soukisian1

1 Institute of Oceanography, Hellenic Centre for Marine Research, Anavyssos, Greece

2 Department of Geology & Geoenvironment, University of Patras, Greece

Introduction

This chapter reviews the main environmental factors which have controlled the evolution of the submerged prehistoric landscape and therefore influenced prehistoric human migration and activity, and discusses the potential for the survival of prehistoric cultural and natural remains on the sea floor of the continental shelf in the Aegean region. For the purpose of this chapter, under the term ‘Aegean region’ we consider the Aegean Sea including the Ionian, Libyan and Levantine side of the Hellenic Arc (Fig. 15.1).


Map shows morpho-bathymetry in Mediterranean Sea with Hellenic Arc including Ionian sea and Aegean sea, Black sea, Levantine sea, Ligurian sea, et cetera.

Figure 15.1 Morpho-bathymetry map of the Mediterranean Sea, Brosolo et al. (2012), with location of the Aegean region and Hellenic Arc. Reproduced with permission from CGMW/UNESCO.

The overall geodynamic outline and the morpho-tectonic structure of the Aegean region provide the framework for discussion of the morphological evolution of the continental shelf. On the basis of the variable geomorphological configuration of the coastal and shelf areas we propose to divide the Aegean region into nine blocks, each of which has its own natural and morphological characteristics and evolution. A short description of the geological and tectonic background will provide the necessary basic information for the assessment of the natural resources available for human settlement. We use the available paleomorphological reconstructions of the exposed landmasses during the major low sea-level periods of the Late Pleistocene to define target areas for submerged landscape surveys. A brief description of the Last Glacial Maximum (LGM) and post-LGM climatic conditions as derived from numerous examples of paleo-oceanographic and paleoclimatic research provides the environmental framework. The present overall wind and wave climate in the eastern Mediterranean and Aegean seas enables us to identify the coastal areas protected from or exposed to wave erosion, and to assess the potential survival of shallow submerged prehistoric remains. It is certain that the wind and wave climate has changed significantly over the course of the last 20,000 years. It is also reasonable to suggest that the relative effect of winds of a given strength from a given direction would be the same, allowing for changes in coastline.

The aforementioned environmental factors are used to describe the characteristics of the nine individual geomorphologic blocks of the Aegean region, with particular reference to the potential survival of natural and archaeological prehistoric remains on the shelf. We conclude with suggested potential example areas for future work on prehistoric submerged landscape and archaeology survey in the Aegean region.

Geodynamic Outline and Morpho-tectonics

The eastern Mediterranean domain (Fig. 15.1) is a unique environment in terms of active geodynamics, plate movements, ongoing geological processes, formation of new and increased relief, and destruction of older morphological structures.

The oceanic crust below the Ionian and Levantine sea basins represents the last remnant of the Tethys Ocean, a 200-million-year-old ocean, which disappeared because of the convergent motion between the Eurasian and the African-Indian continents. The collision of these two continental masses gave birth to some of the highest mountain ranges on Earth, like the Himalayas, Alps, Caucasus and others. Currently, the last remnant of this ocean is being consumed by the fast (5 mm/year) Africa–Eurasia convergence and associated north-northeastward subduction beneath the Hellenic Arc. Active subduction processes and ongoing migration of the continental and oceanic crustal blocks has led to the formation of a complicated geodynamic structure. Convergence between the African plate and the Hellenic fore-arc is nearly perpendicular along western Crete and highly oblique (30°) in the eastern Hellenic fore-arc as far as Rhodes (Fig. 15.2).


Map shows increasing curvature of Hellenic arc with Eurasian plate at top (North) and African Plate at bottom (South) with deformation front having relative motions like HE, AE, HA, et cetera.

Figure 15.2 Increasing curvature of the Hellenic Arc, and changing angle of convergence between the African and Eurasian continents along the Hellenic forearc since 11 Ma (Late Miocene), together with reconstructed paleogeography of the Aegean region using a Mercator projection of modern coastlines. Ten Veen and Kleinspehn (2002). Reproduced with permission from John Wiley & Sons.

The curvature of the Hellenic plate boundary and consequent obliquity of convergence has increased systematically since the Middle/Late Miocene. This has been attributed to several processes including rollback of the subduction interface induced by the slab-pull force of the downgoing African slab (Le Pichon & Angelier 1979; Angelier et al. 1982; Le Pichon 1982; Meulenkamp et al. 1988), gravitational body forces associated with over-thickened Alpine crust (e.g. Le Pichon et al. 1995; Jolivet 2001) and westward extrusion of the Anatolian block along the North Anatolian Fault (Taymaz et al. 1991; Le Pichon et al. 1995).

The boundaries of the actively deforming part of the Aegean region are defined by the following geotectonic features (Fig. 15.3):

  1. The westward prolongation of the dextral, strike-slip North Anatolian Fault (NAF) into the Aegean Sea along the North Aegean Trough (NAT) marks the boundary between the Eurasian continent to the north and the deforming Aegean region to the south. The North Aegean Trough comprises a series of deep basins developed due to transtension along the westernmost segments of the NAF.
  2. The Hellenic Trench, a series of deep elongate basins aligned along the Hellenic Arc defines the southeast, south and southwest boundary between the Aegean continental block and the East Mediterranean Ridge, the accretionary prism developed above the north-northeastward subduction of east Mediterranean oceanic crust.
  3. The Kephallinia Transform Fault (KF), a SSW–NNE trending strike-slip fault, which separates the active part of the Hellenic Arc to the south-east from the inactive one to the north.
  4. The Central Greece Extensional Zone, a diffuse boundary, an area of active extensional deformation, which accommodates the transfer of stress between the northern tip of the Kephallinia Fault and the southwestern tip of the North Anatolian Fault.


Image shows geotectonic boundaries and features over scale ranging from 4 to 5120, where Cyclades Plateau, Hellenic volcanic arc, Central Greece extensional zone, Levantine, et cetera.

Figure 15.3 Main geotectonic boundaries and features of the Aegean region (Aegean Sea, Hellenic Arc and back-arc region) drawn on shaded relief map. Onshore morphology and offshore bathymetry are extracted from the Morpho-Bathymetry Map of the Mediterranean Sea (Brosolo et al. 2012). KF = Kephallinia Transform Fault; NAT = North Aegean Trough; NAF = North Anatolian Fault. Hellenic Volcanic Arc: Me = Methana; Mi = Milos; Th = Thera; Ni = Nisyros. Brosolo et al. (2012). Reproduced with permission from CGMW/UNESCO.

The main, ongoing processes that dominate the geodynamic evolution of the Hellenic region are: the westward extrusion of the Anatolia continental block along the North Anatolian Fault; the N–NNE subduction of the eastern Mediterranean lithosphere beneath the Hellenic Arc; the subsequent SSW–NNE extension of the Aegean back-arc region; the collision of northwest Greece with the Apulian block in the northern Ionian Sea north of the Kephallinia Fault; and the incipient collision with the Libyan promontory south of Crete (McKenzie 1970; 1978; Dewey & Şengör 1979; Le Pichon & Angelier 1979; Le Pichon et al. 1982; Meulenkamp et al. 1988; Mascle & Martin 1990; Meijer & Wortel 1997; Jolivet 2001; Armijo et al. 2004; Kreemer & Chamot-Rooke 2004) (Fig. 15.2).

The active, long-term, geodynamic processes, crustal movements and deformation of the Aegean region give birth to violent, short-term, catastrophic geological events. Build-up of stresses along the boundaries and in the interior of the Aegean region leads to brittle (and ductile) deformation in the upper crust, expressed with normal, reverse or strike-slip faulting. Vertical tectonics along major and minor faults create a puzzle of small-scale blocks which move vertically, either positively (uplift) or negatively (subsidence). Uplifting blocks are being eroded while subsiding blocks host sedimentary basins which receive the products of erosion. Submarine landslides are frequent along the steep, on/offshore, faulted slopes and are very commonly triggered by strong earth tremors.

Subduction of the eastern Mediterranean lithosphere beneath the Hellenic Arc and the subsequent melting of the downgoing sediments and rocks result in spectacular volcanoes and related volcanic structures in the southern Aegean Sea. The volcanoes are aligned along a 500 km-long by 40 km-wide concave arc, known as the Hellenic Volcanic Arc. Volcanic eruptions, on/offshore and coastal faulting, and submarine landslides have triggered numerous (large and small) tsunamis, some of which have caused devastation in many parts of the Aegean, Ionian and eastern Mediterranean coastlines. All of these processes have played a major role in the morphological evolution and configuration of the Aegean region's continental shelf and have modified the effect of Late Pleistocene sea-level fluctuations.

Geomorphology

The variety of active geological and tectonic processes in the Aegean region has created a puzzle of smaller blocks, each characterized by its own geomorphological evolution and configuration, which may be significantly different from the adjacent blocks. This is particularly the case for the coastal and shelf areas.

The southern and eastern parts of the Hellenic Arc, from the southern Peloponnese to Crete and to Rhodes, are characterized in general by fast, but not uniform, uplift, and are segmented by numerous faults which cross-cut the general trend of the arc (Fig. 15.4). On the top of the uplifted blocks, the islands of the Hellenic Arc rise well above sea level and are separated by narrow but deep, faulted trenches. The shelf around the mostly rocky coasts of the islands is very narrow, and nowhere exceeds a few kilometers in width.


Image described by caption and surrounding text.

Figure 15.4 Morpho-bathymetry map of the Aegean region (Aegean Sea & Hellenic Arc) extracted from the IOC-IBCM bathymetry of the Mediterranean (IBCM Project, Intergovernmental Oceanographic Commission, International Hydrographic Organization, and Head Department of Navigation and Oceanography, Russian Federation with permission), and divided into blocks according to the nature of the active morpho-tectonic processes, evolution and configuration of the coastal and submerged landscape. Source: www.ngdc.noaa.gov/ mgg/ibcm/bathy/IBCM-Bathy-5M-254m-Shaded.jpg. Reproduced with permission from IOC/UNESCO.

The western part of the Hellenic Arc, from Corfu in the north to the southern Peloponnese in the south, displays a similarly narrow shelf. The Ionian Margin hosts the deltaic plains of some of the largest rivers of Greece. The shelf reaches its maximum width of up to 15 km to 20 km off the river deltas but in most areas the shelf width does not exceed 2 km to 5 km.

The Aegean Sea between the North Aegean Trough and the South Aegean basin includes the great majority of the numerous islands and islets which comprise the Aegean archipelago. Many, like the Cyclades Islands, are separated from each other by shallow shelves. Others, like the east and northeast Aegean Islands, the east Dodecanese and the north Sporades Islands, are joined to each other and to the adjacent landmasses of Greece or Turkey by shallow shelves. Two island bridges, a southern one in the central Aegean and a northern one in the north Aegean Sea, connect mainland Greece with the landmass of Turkey.

The North Aegean shelf, north of the North Aegean Trough, is the widest one in the Aegean region. The largest rivers of the southern Balkan Peninsula flow from the mountains of northern Greece and outflow here, feeding the shelf with huge quantities of new sediments.

Further bathymetric and morphological data for the Mediterranean Sea can be obtained from the following websites:

Geological and Tectonic Background

The Aegean region belongs to the Alpine orogenic belt, a mountain chain which starts from the Pyrenees and the Alps in the west and continues over the Balkan Peninsula, Anatolia and the Caucasus Mountains to the Himalayas and further east. The geological structure of the Aegean region (Fig. 15.5) resulted from the successive closure of different parts of the Mesozoic Tethys Ocean and evolved in the course of four orogenic cycles from the Dogger (Middle Jurassic) to the Miocene. The orogenic activity and the associated mountain-building processes migrated from the internal (north/northeast) to the external (south/southwest) regions of the Hellenic Arc. The present arc-shaped configuration and rupturing derives from the overprinting of the present geodynamic regime on the Alpine structure.


Map shows geological and morpho-tectonic of Aegean regions with Variscan granitoids, Cenozoic-Quaternary alkaline volcanics, Alpine granitoids, Quaternary sediments basins, et cetera.

Figure 15.5 Geological and morpho-tectonic map of the Aegean region, extracted and modified from the Geological and Morpho-Tectonic Map of the Mediterranean Domain. Mascle and Mascle (2012). Available online at ccgm.org/en/maps/131-carte- geomorphologique-et-tectonique-du-domaine- mediterraneen-9782917310137.html. Reproduced with permission from CGMW and UNESCO.

The bulk geology of northern Greece, the north and east Aegean islands and northwestern Turkey comprises Alpine and Pre-Alpine metamorphic rocks of the internal metamorphic belt and sedimentary and volcanic rocks of Mesozoic and Cenozoic age which form the mountainous regions. Extended Quaternary and alluvial plains predominate close to the north Aegean coasts and are associated with major river-delta formations.

The eastern part of the Greek mainland, the central Aegean archipelago, and the Greek-facing coasts of Turkey are mostly built of Alpine sedimentary rocks and metamorphic rocks of the median metamorphic belt. Volcanic rocks of Quaternary age and active volcanoes occur in the central Aegean Island Bridge. The mountain chain of western Greece, from Epirus in the north to the southern Peloponnese to the south and through the islands of the Hellenic Arc to southwest Turkey, consists predominantly of folded and thrusted sedimentary rocks of Mesozoic to Cenozoic age.

Late and Post-Alpine, Oligocene to Miocene and Pliocene sedimentary deposits occur in various regions between the Mesozoic mountain chains, filling back-arc and molassic basins arranged parallel to the Alpine trend or neotectonic, Plio-Quaternary grabens cutting across the Alpine trend.

The North Aegean Trough (NAT) is the most impressive and actively evolving structure. It developed as a series of isolated, deep basins along the westward prolongation of the North Anatolian Fault. The NAT separates the relatively non-deforming North Aegean shelf from the deforming Aegean region to the south. Similar structures parallel to the NAT occur further south, between and within the north and central Aegean island bridges.

Extensional tectonics in central Greece has created a series of neotectonic grabens, which at present form marine gulfs connected to the open sea through narrow and shallow straits. The Gulf of Corinth, the north and south Evia Gulf, the west Saronikos Gulf, the Amvrakikos Gulf and the Pagasitikos Gulf have developed in the Quaternary, so that during the low sea-level period of the LGM (and probably during older glacial periods?) they were isolated from the open sea and became lakes. Volcanic explosive activity is one of the major issues in the geological evolution of the Aegean region during the Quaternary. The main volcanic centers are located along the volcanic arc in the south Aegean Sea. Large and minor volcanic eruptions have repeatedly modified the landscape of the areas adjacent to the volcanoes in the Late Pleistocene and Holocene.

The Hellenic Arc, extending from the Ionian Islands to the north-west through the south Peloponnese and Crete to Karpathos and Rhodes to the south-east, has developed above the north-northeastward subduction of the east Mediterranean crust and is one of the most active geological structures worldwide. Frequent large earthquakes nucleated on major active faults of the crust, as well as long-term tectonic movements, create a puzzle of uplifting or subsiding tectonic blocks. Vertical tectonic movements along the Hellenic Arc and in other areas of the Aegean region significantly modify the relative coastal effect of Quaternary sea-level fluctuations. Deposition of fine-grained sediments, mostly silt and clay, prevails in the deep-marine areas and basins of the north and south Aegean Sea during the Holocene.

Late Pleistocene Morphological Configuration

Recently, on the basis of systematic sub-bottom seismic profiling data (AirGun, Sparker and 3.5 kHz), Lykousis (2009) has been able to correlate up to five (vertically) successive Low-System-Tracts (LST) — prograded sequences below the Aegean marginal slopes. The LST sequences suggest shelf-break delta progradation at low sea-level stands (glacial periods) during Marine Isotopic Stages (MIS) 2, 6, 8, 10 and probably 12 (the last 400 kyr). Their upward conformable succession at increasing depths and the assumption that they have been deposited in comparable sea-level stillstands, indicates continuous subsidence of the Aegean margins during the last 400 kyr. Subsidence rates of the Aegean margins were calculated from the vertical displacement of successive topset-to-foreset transitions (palaeoshelf break) of the LST-prograding sediment sequences.

A major aspect to be taken into consideration for the reconstruction of submerged landscapes and the elaboration of local sea-level curves in the Aegean region is the role of active tectonics (Pirazzoli 1988; Lambeck & Purcell 2005; Lykousis 2009). Firstly, because active tectonics are an important mechanism in landscape evolution, and secondly because differential vertical tectonic movements accommodated by faults have created a complex pattern of tectonically stable, uplifted and subsiding areas, which modifies the general effects of eustatic sea-level rise.

On the basis of available marine geological, sedimentological and tectonic data and the modeled or calculated sea-level fluctuations during the Middle and Late Pleistocene, Lykousis (2009) has reconstructed the paleomorphological configuration of the Aegean region for the most pronounced low sea-level periods of MIS 2, MIS 6, MIS 8 and MIS 10/12. In Fig. 15.6 we use paleomorphological reconstructions from Lykousis (2009) and draw the boundaries of the nine geographic blocks proposed in Fig. 15.4. In the following section, we show that the proposed blocks represent areas with distinct histories of landscape evolution since the Late Pleistocene.


Images show paleographic reconstruction of Aegean region during major glacial stages of last 400 kyr with MIS 12/10: 480–350 ka; MIS 8: 300–250 ka; MIS 6: 180–140 ka; and MIS 2: 30–18 ka.

Figure 15.6 Modified fig. 5 of Lykousis (2009): Paleogeographic reconstruction of the Aegean region during the major glacial stages of the last 400 kyr (MIS 10/12, 8, 6 and 2), and outline of the nine morphological blocks proposed in Fig. 15.4 superimposed on the four maps. Color code of exposed land: light gray for present landmass configuration; dark gray for exposed landmasses during low sea-level stages.

LGM and Post-LGM Climate

The paleoclimatic records of the LGM in the eastern Mediterranean suggest that the region was generally cooler and more arid than present. The aridity most probably caused a retreat of the paleoglaciers, which appear smaller in comparison to the previous Pleistocene period (Pindus Mountains; Hughes & Woodward 2008). Annual temperature and precipitation in Greece were lower than today by ca. 10°C and ca. 550 mm respectively (Peyron et al. 1998; Tzedakis et al. 2002). The climate influenced the vegetation, and almost all pollen records from marine and terrestrial sediments suggest the dominance of steppic and semi-desert elements (Artemisia, Chenopodiaceae, Ephedra; Bottema 1974; Aksu et al. 1995; Digerfeldt et al. 2000; Lawson et al. 2004; Kotthoff et al. 2008a; Geraga et al. 2010). However, the abundance of Chenopodiaceae and Ephedra during this period may also partly be connected to sea-level changes (van Andel & Lianos 1984; Geraga et al. 2008; Kotthoff et al. 2008a).

Despite the dominance of herbs, there was always a moderate abundance of tree taxa, especially oak and Pinus (Tzedakis et al. 2002). This vegetation pattern is not uniform and depends on local moisture availability, and local topography that provided shelter from incursions of polar air (Tzedakis et al. 2002). Therefore, in western Greece the relatively high precipitation caused by orographic uplift of moist air from the nearby Ionian and Adriatic seas resulted in the persistence of thermophilous trees at mid-altitude sites in contrast to eastern Greece (eastern Pindus mountains) where moisture was lower and the presence of temperate taxa was minimal except probably along coastal plains.

The low temperature is also demonstrated by the low sea-surface temperatures (SST) that prevailed in this period, indicated by the heavy δ18Ο values of surface plankton, ranging between 2‰ and 4.7‰ in the Aegean, Ionian and adjacent seas (Vergnaud-Grazzini et al. 1986; Aksu et al. 1995; Emeis et al. 2000; Geraga et al. 2000; Geraga et al. 2005), and the dominance of cold planktonic foraminifera and dinoflagellate cyst associations (Thunell 1979; Aksu et al. 1995; Casford et al. 2002; Geraga et al. 2008; 2010). Models based on the distribution of the planktonic associations and the stable isotopic signal indicate that the SST was lower than today by 4°C to 6°C (Thunell 1979; Aksu et al. 1995; Hayes et al. 2005; Kuhlemann et al. 2008). The water column was characterized by homogeneity as is seen in the similar isotopic signal obtained from planktonic specimens dwelling in different water masses (Casford et al. 2002), and high eutrophication based on microfaunal and microfloral compositions and the increase of marine biomarkers (Gogou et al. 2007). In addition, benthic foraminifera associations indicate moderate-to-high organic matter fluxes and well-ventilated conditions on the sea floor (Kuhnt et al. 2007). A general climatic improvement is indicated in the proxies of terrestrial and marine sediments during the Late Glacial Period. The climatic improvement is not gradual and monotonic, but presents brief variations between warm and/or humid interstadials and cold and/or arid stadials. These oscillations are associated with the prevalence of the interstadials GI 1a, GI 1c and GI 1e and the relative colder GI 1b and GI 1d and the stadial GS 1, according to the INTIMATE-stratigraphy (Lowe et al. 2008) (INTIMATE — INTegration of Ice-core, MArine and TErrestrial records group of the INQUA Palaeoclimatic Commission). The detection of this climatic variation during the Late Glacial Period suggests a direct response of the southern Balkans to centennial- and millennial-scale climatic variability recorded in northern latitudes. GI events correspond to the Meiendorf/Bølling/Allerød complex, and there is no clear discrimination between them in the climatic data. During the warm intervals (GI 1a, 1c, 1e), despite the persistent dominance of steppe elements in the pollen records, the increase of trees (mostly broadleaved taxa) suggests an increase in moisture availability (Digerfeldt et al. 2000; Lawson et al. 2004; Kotthoff et al. 2008a).

On the other hand, depletion in δ18Ο values in combination with a reduction in the abundance of cold marine microfauna and microflora indicates an increase in SST (Geraga et al. 2008; 2010; Triantaphyllou et al. 2009). Alkenone SST estimation shows that the temperature of the surface waters ranged between 21°C and 24°C in the Ionian and Aegean seas (Emeis et al. 2000; Gogou et al. 2007). Higher abundance of terrestrial biomarkers (Gogou et al. 2007) indicates this relatively warm and humid interval in the Aegean Sea. Furthermore, the increase in freshwater budget (due to Termination 1a) would have increased surface buoyancy leading to the establishment of seasonal (summer) stratification (Casford et al. 2002) and to a change in benthic faunas from oxic to dysoxic indicator species (Kuhnt et al. 2007). GS 1 is the most pronounced in the climatic records of the Late Glacial Period and corresponds to the Younger Dryas event. GS 1 is characterized by a paleoglacier re-advance in high altitude areas (Hughes & Woodward 2008), the expansion of steppic elements (Digerfeldt et al. 2000; Lawson et al. 2004; Kotthoff et al. 2008a; Geraga et al. 2010), enrichment in δ18Ο values accompanied with increases in the abundance of cold marine microfauna and microflora (Geraga et al. 2008; 2010; Triantaphyllou et al. 2009) and a decrease in alkenone SST to 14-16°C, in the Aegean and Ionian seas (Emeis et al. 2000; Gogou et al. 2007). Planktonic and benthic foraminifera data, together with the isotopic signal, suggest a strengthening of winter convection, at least in the Aegean Sea (Casford et al. 2002; Kuhnt et al. 2007).

Climatic instability also characterizes the warm Holocene epoch. Among the Holocene climatic events, the most pronounced is detected between 9.5 ka BP and 6.5 ka BP and is characterized by an increase in precipitation (>270 mm, during winter in northern Greece; Kotthoff et al. 2008b) and an increase in temperature (>4–6°C, during winter in northern Greece; Kotthoff et al. 2008b). The increased precipitation of that time has been related to the strengthening of the southern monsoonal system (Rossignol-Strick et al. 1982; Rossignol-Strick 1983; Aksu et al. 1995) and is reflected in pollen records by the increase of trees and the dominance of deciduous forests. In marine sediments it is evidenced by the deposition of sapropel S1 (Anastasakis & Stanley 1984). Increased temperature, and enhanced freshwater inputs from the outflow of rivers into the Aegean Sea which were later supplemented by the overflowing of the Black Sea (6.5 ka BP; Sperling et al. 2003), lowered the sea surface density and reduced the vertical water mass circulation resulting in reduced bottom-water ventilation.

The reduction of O2 supply to the seabed in combination with increased fluxes of terrigenous and/or marine organic matter were responsible for the creation of dysoxic to anoxic conditions on the seabed, which led to the formation of sapropel S1 (Rohling & Gieskes 1989; De Rijk et al. 1999; Geraga et al. 2000; Casford et al. 2002; Triantaphyllou et al. 2009). The establishment of warm temperatures and low salinity is documented by the large depletions in the isotopic signal (Vergnaud-Grazzini et al. 1986; Aksu et al. 1995; Emeis et al. 2000; Geraga et al. 2008) and the increase in eutrophication is documented by the increase of marine and terrestrial biomarkers (Gogou et al. 2007). Sapropel S1 appears in two layers (S1a and S1b). The interruption of S1 centered at 8.2 ka BP and the end of sapropel deposition coincides with the prevalence of stadials (Rohling et al. 1997; Geraga et al. 2000). The establishment of these two stadials is suggested in alkenone SST records, which show a 2.5°C reduction (Gogou et al. 2007), and in climatic models (based on pollen data), which show a 2°C reduction of winter temperatures (during both intervals), and weaker winter precipitation at the end of sapropel S1 (Kotthoff et al. 2008b). Almost all records suggest that climatic variations also prevailed during the last 6 kyr, although their exact dating is not yet clearly defined. However, it seems that the climate was warmer and more humid between 5.8 ka BP and 4 ka BP (Pavlopoulos et al. 2006; Triantaphyllou et al. 2009; Geraga et al. 2010) than in the previous and following intervals. Most of the Holocene stadials that have been detected in marine and terrestrial sediments coincide with the prevalence of stadials occurring at northern latitudes (Bond et al. 1997) suggesting a direct atmospheric link between the regions. Rohling et al. (2002), examining Holocene data from marine records, suggested that strengthening of the Siberian High results in stronger outbreaks of northerly air flows and thus in lower SSTs.

Overview of the Present Wind and Wave Climate

The overall description of the wind and wave climate of the seas in the Aegean region is based on a 10-year hindcast time series. The wind and wave data for the examined period (1995–2004) have been generated by a non-hydrostatic weather model (an improved version of the SKIRON/Eta model) and a 3rd generation wave model (WAM Cycle-4 model), using a spatial resolution of 0.1° × 0.1° and a temporal resolution of three hours. The results of the models (wind speed Uw, significant wave height Hs and spectral peak period Tp) were calibrated (corrected) with collocated in situ measurements referring to the joint time window 1999–2004. The length of the time series and the spatial and temporal resolution of the hindcasts ensure a statistically reliable assessment of the corresponding wind and wave climate.

The Aegean Sea is a semi-closed basin with many groups of islands. In combination with relatively short fetch durations and lengths and relatively low swells, the overall wind and wave climate of the Hellenic seas, on an annual basis, appears quite mild. Nevertheless, extreme weather and wave phenomena appear in specific areas, characterized by peak values and short durations. These areas are usually straits, where the wind speed and wave heights are significantly intensified due to the channeling effect. Relatively long fetch lengths are observed in the Libyan and Ionian seas, located on the periphery of the Hellenic Arc, as shown by the dashed line in Fig. 15.7a. The significant effects of the fetch lengths are evident specifically in the straits between Kythera and Crete (Area B, west Cretan Strait), Kasos and Crete, as well as Karpathos and Rhodes (Area C, east Cretan Strait). Swell waves are also observed in these specific areas and are characterized by relatively small values for wave height.


Map shows areas of intense wind and wave regime for Hellenic seas and images show spatial distribution of annual wind and annual significant wave height.

Figure 15.7 (a) Areas of intense wind and wave regime for the Hellenic Seas; (b) Spatial distribution of mean annual wind speed; (c) Spatial distribution of mean annual significant wave height. Note that occurrence of maximum annual wind speed and significant wave height coincides largely with the spatial distribution of the mean values.

The most intense wind and wave conditions on a mean annual basis, as obtained from numerical models, are observed in three explicitly defined areas of the Hellenic seas (Fig. 15.7a):

A general feature is that wind and waves propagate from the edge of the Dardanelles Strait to the south Aegean Sea, initially with north–northeast directions at the Dardanelles Strait, ending with northwest directions in the south Aegean (see Axis A, Fig. 15.7a). The directions of propagation of wind and waves are generally in good agreement. The weather and wave systems relax partly in the Cyclades archipelago, resulting in milder — on a mean annual basis — wind and wave conditions. On the other hand, while the northeast Cyclades act as a breaker to the propagation of waves and wind flow from the northern part of the Aegean Sea, they simultaneously drive and amplify, by means of a channeling effect, the corresponding wind and wave fields, mainly to the southeast areas. Thus, in specific straits of the Cyclades archipelago, wind and wave intensities higher than those in the neighboring areas are quite frequently observed. Along the south part of the propagation axis, which extends in an arc form from about the straits between Mykonos and Ikaria to the north-east, there is a specific area north of the Cyclades complex (in the central Aegean), where the intensity reaches its local maximum. In this area, the overall maximum of wind speed and significant wave height for all Hellenic seas during the 10-year hindcasts was detected.

The situation is simpler for the Ionian Sea, since it is an open sea area. It is characterized by wave propagation and wind-flow patterns of various directions. However the prevailing wind and wave systems are those originating from the east Italian coasts, Taranto Bay and the north Adriatic coasts heading towards the western coasts of the Peloponnese and Ionian islands. The fetches corresponding to those directions are significantly longer than in the Aegean (400–500 km from the east Italian coast, 800 km from the north Adriatic coast) as well as the ones from the south–southwest directions (700–800 km from the African coast). Consequently, the offshore areas of the Ionian Sea exhibit — on a mean annual basis — the highest wave potential. The local wind and wave maxima are detected along the Hellenic Arc, particularly in areas B and C. The annual spatial distribution of wind speed and significant wave height is presented in Fig. 15.7b and 15.7c.

For a detailed wind and wave climate analysis of the Hellenic seas see Soukissian et al. (2008a,b). More information on oceanographic and atmospheric data for the Mediterranean Sea can be retrieved from several websites including the following:

Preliminary Analysis of Submerged Landscapes and Survey Potential

Very few attempts have been undertaken so far in the Mediterranean and particularly in the Aegean region to explore and reconstruct submerged prehistoric landscapes with the use of modern seafloor mapping techniques (van Andel & Lianos 1984; Perissoratis & van Andel 1988; Perissoratis & Conispoliatis 2003). Most of these pioneering works resulted in the creation of maps and reconstructions generalized over large regions which smooth out topographic details, irregularities and local variabilities. Here we attempt to shed light on the environmental factors which characterize the shelf of the nine geographic blocks (Fig. 15.4) of the Aegean region and which have controlled the survival or destruction of submerged landscapes and prehistoric remains. A more detailed analysis of the role of active tectonics on the vertical movements and the development and preservation of submerged landscapes can be found in Sakellariou and Galanidou (2015).

North Aegean shelf

This is the area with the most extended shelf in the Aegean region. The maximum shelf width of 15 km to 20 km is associated with the gulfs of Thermaikos and Strymonikos and the Samothraki Plateau, between the islands of Thassos and Samothraki. Three large rivers, which drain the eastern part of the Pindus mountain chain, outflow into the Thermaikos Gulf. The Strymon and Nestos rivers flow through the central part of the metamorphic basement of the Rhodope Mountains and outflow into the Strymonikos Gulf and north of Thassos Island respectively. The Evros River drains the eastern part of the Rhodope Massif and outflows in the eastern part of the Samothraki Plateau. All of these rivers transport important quantities of fertile and erosional material from their mountainous catchment areas to the North Aegean shelf. Extensive delta areas with coastal lakes and lagoons have developed near to the river outflows. Narrow and very narrow shelves occur mostly along the three ‘legs’ of the southern Chalkidiki Peninsula, particularly along the two coasts of the Athos Peninsula, the third (eastern) leg.

The North Aegean shelf is located to the north of the northern boundary of the deforming Aegean region and belongs to the ‘non-deforming’, more rigid, Eurasian continent. Moderate seismic activity and earthquakes do occur in the area, associated either with extensional structures mainly on land or with the strike-slip faulting along the North Aegean Trough. Consequently, vertical tectonic movements do not significantly affect the morphological evolution and configuration of the coastal and shelf area.

Systematic sub-bottom profiling performed in the 1980s (Perissoratis & Mitropoulos 1989) indicates that about 5300 km2 of the North Aegean shelf between the Chalkidiki Peninsula and the Samothraki Plateau was exposed above sea level during the Last Glacial Maximum. At least two permanent and a number of ephemeral lakes existed in this area, while Thassos and Samothraki were connected to the main landmass to the north. The presently submerged landscape of the North Aegean shelf is covered by Holocene sedimentary deposits with a thickness of up to 20 m to 25 m.

Following the spatial distribution of the mean annual wind speed and significant wave height of Fig. 15.7, it is evident that the inner parts of the North Aegean shelf, particularly the inner gulfs of Thermaikos and Strymonikos are exposed to weaker winds and lower waves than the outer parts. The southern coasts of the Chalkidiki Peninsula, and the islands of Thassos and Samothraki are exposed to significantly higher wind speed and waves. The preservation or erosion of possible shallow submerged sites is subject to many factors including local oceanographic and coastal dynamic conditions. The use of the mean annual wind speed and significant wave height offers a first approach to assess the potential for preservation or erosion of prehistoric remains on the shallow seafloor.

North Aegean Island Bridge

The Sporades archipelago, the islands of Skyros, Aghios Efstratios, Lemnos, Gokceada and other smaller islets, which are located between the North Aegean Trough to the north and the central Aegean to the south, constitute stepping stones between central Greece and northwestern Anatolia. Most of the islands are surrounded by shallow shelves and many of them were connected to each other during the low sea-level periods of the Late Pleistocene (Fig. 15.6).

During the low sea levels of MIS 12, MIS 10 and MIS 8, the North Aegean Trough was isolated from the open sea, and the north Aegean Island Bridge connected the mainland of Greece with that of northwestern Anatolia. The North Aegean Trough/Lake separated the North Aegean shelf from the north Aegean Island Bridge. During MIS 6, the Sporades archipelago remained connected to the Greek mainland to the west. A shallow sea separated the Sporades Ridge from the exposed land which is attached to northwestern Anatolia and includes the northeast Aegean islands (Lemnos, Gokceada, Aghios Efstratios). The latter remained connected to the Anatolian landmass during the LGM because of the extended exposed shelf.

Active tectonics in this area are more or less associated with the adjacent prolongation of the North Anatolian Fault into the North Aegean Trough and the parallel secondary structures, mostly strike-slip and transtensional. Evidence of vertical tectonic activity is known from Skyros Island. Skyros underwent subsidence during the Holocene either caused by gradual tectonic events or of co-seismic origin as testified by submerged notches (Evelpidou et al. 2012).

The eastern, extended shelf of the north Aegean Island Bridge, together with the North Aegean shelf, are the marine areas most exploited by the fishing industry in the Aegean Sea. Intensive trawling activity constitutes a potential threat to prehistoric remains when exposed on the sea floor. The north Aegean Island Bridge belongs to the area of highest mean annual wind velocity and significant wave heights in the Aegean Sea (Fig. 15.7). It is therefore reasonable to expect a highly dynamic regime along the coastal zones, especially those facing the open sea.

East Aegean islands

The two largest islands, Lesvos and Chios, remained connected to the Anatolia landmass during all the major low sea-level periods of the last 500 kyr. During the low sea levels of MIS 12, MIS 10 and MIS 8, a large lake occupied the central Aegean area, between the north Aegean Island Bridge and the eastern Aegean islands to the north and the central Aegean Island Bridge to the south. The lake consisted of several deep basins developed along major tectonic lineaments and separated the exposed eastern Aegean islands from the Greek landmass to the west. After MIS 8, the lakes of the central Aegean and the North Aegean Trough never formed again. The basins remained connected to the open sea through shallow sea areas.

Several harbor installations of the Classical and Hellenistic periods have been discovered along the coast of Lesvos Island, submerged at 1 m to 2 m below present sea level (Williams 2007; Theodoulou 2008). Relative subsidence of the island is mostly attributed to glacio-isostatic adjustment (GIA) associated with eustatic sea-level rise, although tectonically-driven vertical movements cannot be ruled out. The exposed shelf of the east Aegean Islands receives the fertile material discharged by two major rivers, the Bakir Çayi and Gediz, which drain the mountainous central part of western Anatolia.

Central Greece

The block of central Greece, as defined here, coincides roughly with the Central Greece Extensional Zone, an area of Quaternary and active extensional tectonics. A series of WNW–ESE trending neotectonic grabens have developed within this regime, and at present have the form of marine elongate gulfs cutting across the Alpine structure of the Hellenides mountain chain. The 900-m-deep Gulf of Corinth and the 450-m-deep north Evia Gulf are the largest and most active grabens in central Greece. The Amvrakikos, south Evia, Pagasitikos and west Saronikos gulfs are smaller, shallower and less active. These water bodies have one characteristic in common: at present they are connected to the open sea through narrow and shallow straits with sills which were exposed above sea level during the LGM. All of these gulfs were disconnected from the open sea during the LGM as demonstrated by the presence of lacustrine, aragonite-bearing deposits below the sea floor (Lykousis & Anagnostou 1993; Perissoratis et al. 1993; Lykousis et al. 2007; Sakellariou et al. 2007a,b).

These water bodies were all isolated lakes surrounded by fluvial plains and high mountains. With the exception of the Gulf of Corinth and the north Evia Gulf, the rest are characterized by relatively extended shallow areas which were exposed above sea level during the LGM. The first two gulfs are subject to fast, active, vertical tectonics, with subsiding and uplifting movements which modify significantly the effect of sea- or lake-level fluctuations (Armijo et al. 1996; Leeder et al. 2005; Lykousis et al. 2007; Sakellariou et al. 2007b; Evelpidou et al. 2011). These gulfs are effectively protected from strong winds and high wave activity. Although erosional processes do occur along parts of their coasts, they are mostly controlled by very local conditions and/or anthropogenic interventions.

The Argolikos Gulf is the only major gulf in the central Greece block which has always been connected to the south Aegean Sea. It has developed as a deep neotectonic graben (Papanikolaou et al. 1994) with an extensive shelf along its eastern margin. Van Andel and Lianos (1984) and Perissoratis and van Andel (1988) have already surveyed this shelf, particularly off the Franchthi Cave, where traces of Mesolithic and Neolithic habitation have been found, and provided generalized reconstructions.

Central Aegean Island Bridge

The central Aegean Island Bridge is a major element in the Quaternary paleomorphological evolution of the Aegean region. It comprises the Cyclades archipelago and plateau, the northern part of the Dodecanese archipelago and the islands of Ikaria and Samos. The Cyclades archipelago is an extended shallow plateau at the southeastward prolongation of central Greece. The northern Dodecanese archipelago comprises many small and larger islands, including Ikaria and Samos, which are connected to each other by an extensive shelf attached to the coasts of the southwestern Anatolia landmass.

During the major low sea-level periods of MIS 12, MIS 10 and MIS 8, a continuous, elongate landmass was exposed in this area and connected central Greece with Anatolia (Fig. 15.6). In the Late Pleistocene, the central Aegean Island Bridge separated the central Aegean Lake to the north from the south Aegean enclosed sea to the south. The Hellenic Volcanic Arc built the southern edge of the exposed landmass. Continuous volcanic activity and violent eruptions at the main volcanic centers in Methana, Milos, Thera and Nisyros episodically modified the landscape during the Late Pleistocene. Since MIS 6, the central Aegean landmass has broken into two main parts. The western one includes the Cyclades Plateau, which initially remained connected to central Greece and was transformed into a large island during the LGM (Kapsimalis et al. 2009). The eastern part includes most of the north and east Dodecanese islands, Ikaria and Samos, and remained attached to the Anatolia landmass during all low-sea-level stages. Broodbank (2000: 112–13) discusses the potential Paleolithic occupation of the Cyclades, and the significance of the reduction in area from a single landmass to scattered islands.

Most of the islands of the Cyclades archipelago, as well as Ikaria and Samos, are built of metamorphic rocks, predominantly schists and marbles of the median metamorphic belt. Metamorphosed granitoids occur as well, especially in the northern Cyclades and Ikaria. The Dodecanese Islands are mostly built of sedimentary rocks, Mesozoic limestone, marls, radiolarites and Tertiary flysch. Post-Alpine clastic deposits, such as marls, sandstones and conglomerates, outcrop on the lower part of some of the islands.

The central Aegean is characterized by relatively low seismicity, an absence of large earthquakes, and minor faulting. Vertical tectonic movements are apparently of minor significance for the paleogeographic evolution of the central Aegean Island Bridge. Therefore, the evolution of the coastline during the Late Pleistocene and Holocene has been mostly controlled by eustatic sea-level fluctuations, and to a lesser extent by isostatic movements. Still, evidence of tectonic subsidence during the last 6000 years in the center of the Cyclades has been observed from evidence of submerged beachrocks (Desruelles et al. 2009).

The eastern part of the central Aegean Island Bridge receives the fertile material of two major rivers which drain the metamorphic Menderes Massif: the first of these, the Küçük Menderes or Cayster River, rises from the Bozdağ Mountains, flows westward and outflows into the Aegean Sea south of Izmir. The Holocene fluvial and deltaic deposits of the Küçük Menderes have silted up the area of ancient Ephesus, an important port in Antiquity, which is now several kilometers inland of the present coastline. The second of these, the Büyük (Great) Menderes or Maeander, is about 600 km long and the largest river in the Aegean region. It outflows south of Samos, feeding the shelf of the east Dodecanese archipelago with clastic sediments derived from the erosion of mountainous southwest Turkey.

The strait between the Cyclades Plateau and the east Dodecanese islands is an area of high annual mean wind velocity and significant wave height (Fig. 15.7). This is also the case for the area north of the central Aegean Island Bridge. Thus, the coasts which are facing these areas are subject to highly dynamic coastal processes related to the wave activity (Fig. 15.8).


Image described by caption and surrounding text.

Figure 15.8 Morphological map of the Aegean region extracted from the IOC-IBCM bathymetry of the Mediterranean (IBCM Project, Intergovernmental Oceanographic Commission, International Hydrographic Organization, and Head Department of Navigation and Oceanography, Russian Federation, with permission). Areas of observed or suspected erosion and sediment accumulation in the shallow coastal zone are marked with rectangles. Circles and ellipses mark areas of coastal sediment accumulation. Data from the Hellenic Centre for Marine Research. Note: more information on coastal morphology and erosion risk at scale 1:100,000 can be retrieved from the CORINE coastal erosion database (Version 1990) at www.eea.europa.eu/data-and-maps/data/coastal-erosion. Reproduced with permission from IOC/UNESCO.

Ionian Margin

The western part of the active Hellenic Arc, the Ionian Margin, belongs to the seismically most active areas of the Aegean region. Seismic activity and tectonic movements are associated with the thrusting of the overriding Aegean crustal block above the subducting Ionian lithosphere, and with the activity of the Kephallinia strike-slip fault (Fig. 15.3). The Ionian Islands and the landscape of the western part of the Greek mainland and of the Peloponnese have resulted from the active tectonic movements along these two major tectonic elements. Mesozoic evaporites, limestones, radiolarites, Tertiary flysch and Late Alpine clastic deposits and Quaternary Post-Alpine sediments form the bulk geology of the Ionian Margin area (Fig. 15.5).

A relatively extended shelf width characterizes the northern half of the Ionian Margin. Most of the Ionian islands were connected to the Greek mainland during the major low sea-level periods of the Late Pleistocene. Several major and minor rivers, which drain the western flanks of the Pindus mountain chain, outflow into the Ionian Sea. Holocene sediment thickness on the shelf close to the river mouths may reach some tens of meters. This is the case, for example, for the shelf area off the Acheloos Delta, in the eastern half of the inner Ionian archipelago (Fig. 15.4). The deltaic plain of the Acheloos River, developed during the Holocene, includes fairly extended lagoons and marshes, and has incorporated several basement hills which used to be islands before the seaward progradation of the delta.

The inner Ionian archipelago comprises many tens of islands of all sizes. It is a shallow, semi-enclosed marine area between the western coast of central Greece and the islands of Lefkas, Kephallinia and Zakynthos (Zante). Most of the islands of the archipelago were connected to each other and the mainland during the LGM and previous low sea-level stages. Opposite the western coasts of the Ionian Islands, the area of the inner Ionian archipelago is protected from strong winds and high waves. Numerous caves, partly or totally submerged, are known to exist along the coasts of the Ionian Islands. The calcareous composition of the prevailing sedimentary rocks favors the formation of karstic caves due to dissolution of limestones, especially in fractured rocks.

Further south, the west coasts of the Peloponnese are exposed to the open Ionian Sea and particularly high waves. The shelf is fairly narrow and becomes negligible along the coasts of the southwestern Peloponnese. Short rivers flow through the mountains of the western Peloponnese and outflow on the west and southwest coasts. Holocene sediment deposition on the narrow shelf is generally low. Mass gravity processes at the edge of the shelf transport significant parts of the sedimentary load to the deep basins of the Ionian Sea.

West Cretan Strait

The west Cretan Strait is one of the two sea straits which separate the island of Crete from the two adjacent landmasses of Greece and Turkey. It includes the southeastern part of the Peloponnese and the islands of Kythera and Antikythera, two stepping stones between the Peloponnese and Crete (Fig. 15.4). The area is known for very high seismic potential and long-term vertical tectonic movements. Uplifted Late Pleistocene marine terraces and Holocene shorelines (Pirazzoli et al. 1982) are evident along the coastline of the southeastern Peloponnese indicating continuous tectonic uplift during the Quaternary as a response to the ongoing subduction of the Ionian lithosphere underneath the overriding Aegean microplate and the deformation of the latter.

The mostly mountainous area of the southeastern Peloponnese is built of Mesozoic and Tertiary sedimentary and metamorphic rocks (limestones, flysch, schists and marbles) and Plio-Pleistocene sediments deposited in Post-Alpine basins. Late Pleistocene and Holocene deposits occur in the restricted lowlands of the river plains and deltas. The shelf off the coasts is fairly narrow and progresses very rapidly to steep submarine slopes leading to the deep basins of the Hellenic Trench to the south-west, or to the deep west Cretan Sea to the east. A shallow, northwest–southeast running ridge connects the islands of Kythera and Antikythera. The shallowest parts of this ridge were exposed during the major low sea-level periods of the Late Pleistocene and were probably connected to the southeastern Peloponnese. During these periods, the width of the strait separating Crete from the Peloponnese was reduced to only a few nautical miles (Fig. 15.6).

In parallel to the prevailing long- and short-term tectonic uplift of the landmasses in this region, local tectonics and faulting is responsible for the formation of the deep basins and trenches and the rough seafloor morphology of the west Cretan Strait. The submerged prehistoric city at Pavlopetri in Vatika Bay close to Elaphonissos (Flemming 1968a,b; 1978; Harding et al. 1969; Harding 1970) is clear evidence of local tectonic subsidence within a long-term uplifting region. The ruins of the submerged city survived on the shallow sea floor because they were covered by coastal sand deposits in a sheltered location protected from the very dynamic wind and wave climate of the west Cretan Strait (Fig. 15.7).

Crete

The largest island in the Aegean region, Crete is located on the leading edge of the south-southwestward-moving Aegean microplate and occupies the southern segment of the Hellenic Arc, which is believed to be in incipient collision with the Libyan promontory of the African continental plate (Mascle et al. 1999).

The geotectonic position of Crete during the active geodynamic regime of the Quaternary is responsible for the very prominent brittle deformation of the island through faulting and large magnitude earthquakes. The largest earthquake in the Mediterranean during the Historic Era occurred on a northeast-dipping fault-plane a few kilometers off southwest Crete (Shaw et al. 2008). That earthquake uplifted western Crete abruptly by up to 8-9 m in the fourth century AD (Pirazzoli et al. 1982).

Initial north–south extension followed by extension in an east–west direction formed the Cretan structural high and divided the island into several tectonic blocks (van Hinsbergen & Meulenkamp 2006) which display slightly different histories of tectonic movements. The high mountains of the island represent the faster uplifting blocks, while the lower parts between them exhibit slower uplift or even relative subsidence episodes (Pirazzoli 1988). This is the reason why, despite the overall trend of uplift of the island as a whole or of the individual tectonic blocks, whether faster or slower, longer or shorter term, there are still areas on the island undergoing subsidence where Bronze Age sites are submerged below present sea level.

Active tectonics is a major factor in the evolution of the landscape on Crete (Fassoulas & Nikolakakis 2005). Thus the steep southern flanks of the island have developed along major, east–west running faults which have created an enormous morphological discontinuity between the >2000-m-high Cretan mountains and the >2000-m-deep basins south of the island. Gavdos Island constitutes the summit of a tectonic block south of Crete, separated from it by a trench 1000 m to 3000 m deep (Fig. 15.3). The island is surrounded by a fairly extensive shelf which used to be exposed above sea level during previous low sea-level periods (Fig. 15.6) but has never been connected to Crete during the Quaternary. The shallow area off the west coast of the Messara basin in central southern Crete is the only place along the southern coastline of Crete with considerable shelf development. The linear morphology and rocky character of the steep west and east coasts of Crete are a good indication of their fault-related development. The sea floor of the straits west and east of Crete display tremendous irregularity with very deep trenches alternating with steep, elongate ridges developed perpendicular to the trend of the Hellenic Arc. Shelf development is more pronounced off the northern coasts of Crete, especially off the wide gulfs which are associated with the slower uplifting tectonic blocks of the island.

All sides of Crete are exposed to very strong winds and wave heights (Fig. 15.7). The rocky nature and steepness of the west, south and east coasts demonstrate that erosion is the dominant process along the coastal and shallow offshore zones. Erosion prevails along the northern coasts of the island too (Fig. 15.8), where it results from exposure to wave action and the numerous artificial interventions and constructions along the shoreline.

East Cretan Strait

The larger islands of Kasos, Karpathos, Rhodes and other smaller ones form an island chain between east Crete and the southwestern edge of the Turkish landmass. The islands of the east Cretan Strait represent the uplifted parts of the southeastern segment of the Hellenic Arc. Due to the progressive curvature of the Hellenic Arc (Fig. 15.3), the southeastern segment trends at low angle or parallel to the motion-path of the down-going plate and is characterized by active strike-slip tectonics (Jongsma 1977; Mascle et al. 1982) and oblique thrusting (Fig. 15.2) (Stiros et al. 2010). Subsequent deformation and uplift of the arc creates extensional tectonics of the upper plate which is manifested by numerous normal and oblique faults.

Like Crete, the east Cretan Strait is segmented into tectonic blocks, each exhibiting its own history of vertical movements. According to Pirazzoli et al. (1989), Rhodes can be characterized by considering a small number of crustal blocks, each one displaying a specific tectonic history. Signs of up to eight stepped Late Holocene shorelines have been recognized and studied along the east coast of Rhodes (Flemming 1978; Pirazzoli et al. 1982; 1989; Kontogianni et al. 2002).

The three main islands are surrounded by narrow shelves which, especially off the eastern coast of Karpathos, are negligible in width. The strait between Rhodes and Turkey is shallow and it is possible that the island was connected to Anatolia during earlier low sea-level periods (Fig. 15.6). Karpathos and Kasos were connected to each other during Late Pleistocene low sea-level periods but were always separated from Crete and Rhodes by deep-sea straits.

The east Cretan Strait is one of the three explicitly defined areas of the Aegean region with the most intense wind and wave conditions on a mean annual basis, as obtained from numerical models (Fig. 15.7). Wind speed values of >11 m/sec and significant wave heights of >4 m are statistically expected fairly frequently every year (Soukissian et al. 2008a,b).

Potential Areas for Future Work

Prehistoric human occupation (Paleolithic to Neolithic) has been documented in many places on the Greek mainland, and the Aegean and Ionian islands, even on remote islands like Crete, which has been separated from any landmass throughout human history (Fig. 15.9). Paleolithic findings include 700,000 year old stone tools from Corfu and Palaiokastro Kozani, the 300,000 year old Neanderthal skull from Petralona Cave in Chalkidiki, a Homo sapiens skull from Apidima Cave in Mani, stone tools from Kokkinopilos in Epirus, and animal traces, teeth, traces of fireplaces and other artifacts from various areas, including the Theopetra Cave close to Kalambaka in Thessaly. The Mesolithic period is mostly known from Franchthi Cave in Argolis and Theopetra in Thessaly. Further Mesolithic evidence has been found at Sidari on the island of Corfu, in the Cyclops Cave on the island of Gioura (Sporades archipelago) and in Maroulas on Kythnos with surviving parts of houses and graves. Neolithic settlements have been found in many places in Greece. Some of the most important excavated sites are in Thrace (Paradimi, Makri), Macedonia (Servia Kozani, Dispilio Kastoria, Drama, Olynthus, Makrygialos Pieria), Thessaly (Sesklo, Dimini, Theopetra, etc.), Attica (Nea Makri), the Peloponnese (Franchthi and Lerna in Argolis, Alepotripa in Mani) and on the Cycladic Islands (Strofilas in Andros, Ftelia in Mykonos, Saliagos in Antiparos, etc.).


Map shows indicative of prehistoric settlements in Aegean region, where Paleolithic is >12kyrs; Mesolithic is 12–10kyrs; Neolithic is 10–5kyrs, which are all in Alonissos, Strofilas, Giali, Sidari, Corfu, et cetera.

Figure 15.9 Indicative (not exhaustive) map of prehistoric settlements in the Aegean region. Modified from Sampson (2006) with permission from Atrapos, Athens.

On Crete (and the island of Gavdos) particularly, recent and older systematic, archaeological surveys have yielded artifacts proving Mesolithic occupation of the island, and evidence of possible Lower Paleolithic occupation dated to over 100,000 years ago (Strasser et al. 2010). The fact that Crete has always been an island during the last million years implies that the early inhabitants reached the island by using open-sea-going vessels and that the history of seafaring in the Mediterranean started in early prehistoric times.

In contrast to the many sites on land, few submerged prehistoric sites are known so far from the Aegean and Ionian seas. The most spectacular site is the Late Neolithic–Bronze Age (sixth to fourth millennium BP) city of Pavlopetri in Vatika Bay in the southeastern Peloponnese, which has survived on the sea floor at a depth of ca. 3.5 m. Further evidence of submerged prehistoric settlements has been found at shallow depths off Plytra in the Peloponnese, in Agios Petros islet (next to Kyra Panagia Island, northern Sporades), in Agios Georgios off the western coast of Corfu, in Platigiali close to Astakos, in Salanti next to the Franchthi Cave (Argolis) and a few other places.

Systematic survey and reconstruction of the submerged landscape of the Aegean region is expected to reveal significant new information on the drowned prehistoric archaeology of the region and will presumably bring to light many unknown sites under the sea. The coastal landscapes exposed at lowered sea level provided relatively fertile and productive refugia for plants, land mammals and humans during the cold, low sea-level periods when increased aridity would have reduced or deterred hinterland occupation (Bailey & Flemming 2008). Therefore, underwater investigation of the shelf is essential for the understanding of early human adaptation and dispersal.

Nevertheless, systematic survey of the shelf areas by means of modern technology is costly and time consuming. Certain criteria and consideration of the environmental factors which may have attracted human occupation can be used to define the most promising areas to be surveyed. The availability of freshwater resources is one of the main factors which make an area attractive for habitation. Water access points include rivers, lakes and freshwater springs. Reconstruction of the course of the rivers and identification of possible lakes can reasonably be a first task for the survey of extended shelves like the North Aegean shelf, the eastern part of the north Aegean Island Bridge, the central Aegean Island Bridge and the inner Ionian archipelago in the Ionian Margin.

Fresh and brackish water karstic springs, submerged at shallow depths below present sea level, are very common in the Aegean region, especially off rocky coasts composed of calcareous rocks (limestone, marble). Karstic springs occur commonly at the interface of the Mesozoic limestone or marble and impermeable formations like Eocene–Oligocene flysch and clastic formations of the Mio-Pliocene. During the Late Pleistocene low sea-level periods, these springs may have constituted attractive freshwater points on the exposed coastal landscape. Most of the known underwater karstic springs in the Aegean region are located on narrow shelves off moderate or steeply sloping coasts. Large underwater karstic springs have been discovered on the eastern shelf of the Messiniakos Gulf (Ionian Margin, southeast Peloponnese), the Ionian Islands (Kephallinia) and off the Ionian coastline of Greece (Ionian Margin), the western shelf and coast of the Argolikos Gulf (central Greece), off the southern and northern steep coasts of the Gulf of Corinth, the north and south gulfs of Evia (central Greece), the northern shelf of Crete and many other areas.

Submerged karstic caves are sites of potential prehistoric occupation. Like karstic springs, the caves are associated with calcareous rocks and their creation is due to the solution of limestone and marble by sea water. Submerged caves have been discovered off the rocky coasts of the Ionian Islands (e.g. Meganisi — Ionian Margin), the south Peloponnese (Mani Peninsula — Ionian Margin and west Cretan Strait), Crete, the Sporades Islands (north Aegean Island Bridge) and many other places.

Opposing coasts on either side of narrow sea-straits may also be of major importance for prehistoric occupation and migration, and thus may host traces of prehistoric human presence. Narrow sea-straits can be found in many places in the Aegean region as major elements of the changing paleogeographic configuration during the Late Pleistocene and Holocene. The island bridges in the north and central Aegean, the east Aegean islands, the west and east Cretan straits and the Ionian Margin, particularly the Ionian Islands and the inner Ionian archipelago, display variable configurations during the successive low sea-level periods and were characterized by narrow sea-straits separating isolated islands from each other and from adjacent landmasses.

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