Introduction

1A fundamental question in the study of early maritime landscapes is the coastline configuration for a specific time period. At the end of the Pleistocene, sea levels oscillated around depths of 40-90 m below present while periodically plunging to less than -120 m during glacial maxima. An exception is Marine Isotope Stage (MIS) 5e when global sea- level was higher than today (see the generalized curve showing the main trends of global sea-level change over the last 200 000 years in the preface to Submerged Prehistory; Benjamin et al., 2011). This led inevitably to a complete alteration of the coastal zone and the disappearance of island archipelagos which probably have facilitated maritime networks throughout prehistory, particularly those of Palaeolithic age (Bailey, 2013). Palaeogeographic reconstructions based on palaeoenvironmental data derived from boreholes provide a fundamental tool for the study of past maritime landscapes. They provide the back- ground evidence for reconstructing the history of sea voyages and the early contexts from which arose efforts to exploit offshore resources. However, as Bailey (2013) pointed out: “Maps of Palaeolithic and Mesolithic site distributions and Pleistocene dispersals rarely show the position of the palaeoshoreline, or else present the submerged Shelf as a blank and largely featureless area – about which little can be known beyond very broad generalization”. The present paper summarizes reconstructions of past coastal landscapes including the island of Lemnos and its broader region, the NE Aegean Sea (Figure 1A). Lemnos has a rich archaeological record which however is mostly confined to the middle of the 4th millennium BC onwards, corresponding to the Final Chalcolithic or the Final Neolithic II Period in Aegean terminology (Chalkioti, 2013). In 2006, the Epipalaeolithic site of Ouriakos (around the middle of the 11th millen- nium BC) was discovered in the southeastern part of the island, and completely revised our archaeological perspective regarding the earliest occupation of this part of the Aegean (Efstratiou et al., 2014; Efstratiou, 2014) (Figure 1B, 5A and 5B). Although Lemnos is relatively well explored, the archaeological evidence of early occupation is scanty. Nevertheless, the available evidence, together with recent discoveries of an early Neolithic settlement on the nearby island of Imvros (Gökçeada in Turkish; Erdoğu, 2011), indicates that we need to re-evaluate our methods of exploration of prehistoric settlements, as well as demonstrating that sea-level changes since the LGM have greatly affected the identification of potential archaeological sites on the island which predate the 4th millenniumBC.

2Key questions regarding the maritime landscape of Lemnos include the following: When did the rise in sea level at the end of the Pleistocene reach the point where Lemnos began to be isolated from the mainland and adjacent islands and form an island? What was the distance across the sea to the mainland once the island began to form? How did this distance change over time? What distance were the identi- fied prehistoric sites from the shoreline at the time of their occupation? These questions clearly apply to many areas (Özbek and Erdoğu, 2014). In order to investigate the maritime landscape of Lemnos and to try to answer these questions it is best to examine Lemnos in conjunction with its neighboring islands and the Northwest Anatolian mainland. However, in order to study past maritime landscapes in given time periods, two types of data are essential: high definition bathymetry and reliable sea-level curves, based on local data that combine strong geochronological evidence and the use of sea-level indicators that have high vertical accuracy (Brückner et al., 2010). Recent palaeoenvironmental studies on Lemnos Island have provided the tools to reconstruct vertical and lateral shoreline positions on the island, particularly from the middle of the Holocene onwards (Pavlopoulos et al., 2013; Vacchi et al., 2014).

Topographical, Geological and Archaeological settings of Lemnos Island

3Lemnos is located in the heart of the North Aegean Sea and is the largest island in the Thracian Sea (the North Aegean between the Chalkidiki Peninsula and the northwest coast of Turkey). The area of Lemnos is 482 km2 and its coastline is 260 km in length. It is ca. 63 km west of the entrance to the Dardanelles Strait. The closest island is Imvros, 33 km to the northeast, while Ayios Efstratios Island is around 37 km to the south-southwest. Lemnos is located on the northwest edge of a shallow underwater threshold (Truva Shelf) which constitutes the western extension of the NW Anatolian mainland (Turkey). The central part of the North Aegean Trough (NAT), with depths reaching more than 1000 m, trends across the northern coastline of Lemnos. For this reason the north-northwestern part of the island’s coastline is steep and abrupt, which continues underwater – in sharp contrast to the eastern side of the island where there are extensive shoals. Accordingly, the highest peak, Vigla (428 m), is located near the northwestern corner of the island (Figure 1B; Chalkioti, 2013). The landscape of Lemnos is relatively low with gentle inclinations. The island’s most distinctive feature is the two large, diametrically opposing gulfs on the north (Pournias Gulf, Figure 1B) and south (Moudros Gulf, Figure 1B) coasts, which provide an abundance of safe anchorages. Moudros Gulf, in particular, is considered to be among the safest anchorages in the Eastern Mediterranean. The formation of these gulfs is related to the fault geometry of the island and the North Aegean Trough.

4Geologically, Lemnos Island consists mainly of Upper Eocene–Lower Oligocene molasse-type sediments which are deposited in a large NE–SW trending Paleogene depocenter embracing the wider area of the North Aegean Sea, as well as the north- western part of the Biga peninsula (the NW part of Anatolia, Figure 1A). Although Lemnos is mainly of volcanic origin, large areas consist of depressions covered with Holocene alluvium, with occasional shallow salt basins and lagoons, mainly along the eastern and north-eastern coast and the innermost part of Moudros Bay (Tranos, 2009; Efstratiou et al., 2014; Pavlopoulos et al., 2013; and Chalkioti, 2013 with maps illustrating the areas with Holocene alluvium).

5Until recently, Lemnos was mainly known for the Bronze Age settlement of Poliòchni and the archaic and classical city of Hephaestia (Efstratiou et al., 2014). Poliòchni’s earliest phases go back to the middle of the 4th millennium BC. More recent explorations have revealed other sites of similar age, or even older, such as Myrina (its earliest phases are assigned to the first half of the 4th millennium BC), Stvi, Vriòkastron, Ayios Ermolaos, and Dermatas (Figure 1B). All of these sites are close to, or situated on, the modern coastline. They were founded on small promontories (Ayios Ermolaos, Myrina) defining small coves and sometimes protected by coastal islets (Stvi), or on low coastal hillocks (Vriokastro), and in some cases near stream estuaries (Poliochni, Dermatas; Chalkioti, 2013). In 2006, the Epipalaeolithic site of Ouriakos (Figure 1B) was discovered, confirming earlier suggestions of the colonization of the Aegean islands well before the Neolithic period (Efstratiou et al., 2014).

Sea Level Studies on the island of Lemnos

6Since there are no local sea-level curves for the Pleistocene and Early Holocene, the sea-level rise delineated in this contribution is based on Lambeck’s ice-volume Equivalent Sea-Level (ESL) curve (Lambeck et al., 2014; Figure 2A with 95% probability limiting values). However, a local curve has recently been compiled covering the time frame from the 7th millennium BP (ca. 5000 cal. BC) onwards (Vacchi et al., 2014; Figure 2B). It is based on palaeoenvironmental data from boreholes extracted from two areas on the NE part of Lemnos, Hephestia in the Pournias Gulf and the Alyki Lagoon (Figure 1B) (Pavlopoulos et al., 2013; Vacchi et al., 2014). It should be noted that this new dataset corresponds well with Lambeck and Purcell’s Mediterranean curve (Lambeck and Purcell, 2005), in particular during the intervals from 7000 to 5000 cal. BP and from 2000 to 1000 cal. BP (Pavlopoulos et al., 2013). This data also confirms the view that the sea level in the Mediterranean rose continuously over the last 6 000 years (Brückner et al., 2010). Although Lemnos is crossed by the tectonically active North Anatolian fault there is no evidence of vertical movement, such as notches above present sea-level (Pavlopoulos et al., 2013); however, this is not the case for Imvros (Koral et al., 2009). The pattern of Holocene Relative Sea-Level (RSL) exhibits significant variability, and therefore it is not possible to define a general RSL curve for the entire North Aegean region. Such variability is particularly evident in the RSL reconstructions older than 4.0 ka BP (Vacchi et al., 2014) (Figure 2B).

7Evidence from boreholes on the northeastern side of Lemnos (Pavlopoulos et al., 2013) shows that between 7050 and 3000 cal. BP (5100 to 1040 BC, sea level -7 m to -2 m) an extensive shallow marine environment with freshwater inputs existed on the eastern side of Lemnos (Aliki; Figure 4D). In the period between 2820 and 1130 cal. BP (1040 BC-760 AD), Aliki was transformed to a mesohaline lagoon and then to a shallow bay environment with a moderate sedimentation rate. It should be noted, however, that palaoenvironmental developments in this area were probably affected by the Black Sea outflow, starting between 8000 and 7000 cal. BP (Sperling et al., 2003; Gogou et al., 2007; Kouli et al., 2012) and reaching its maximum around 5000-4000 cal. BP. River discharges from the Balkans and Turkey are an additional factor affecting the geomorphological setting of this coastline (Pavlopoulos et al., 2013).

Methods

8The basis of this survey is “Sonar Charts^TM”, available from Navionics, a company specializing in electronic navigational charts. SonarCharts^TM is a High Definition (HD) bathymetric map, including bottom contour detail, and is extremely useful for the study of shallow water areas. It also reveals changes in bottom conditions by incorporating sonar logs with existing data http://www.navionics.com/en/company). Geographic Information System (GIS) software provides the opportunity to reconstruct past coastlines by digitizing the local high definition bathymetry, creating a bathymetric Digital Terrain Model (DTM) and comparing it with temporal sea- level fluctuations based on the available palaeoenvironmental data.

9Twenty-five partially overlapping sonar charts at different scales, accessed between October 2014 and March 2015, were imported into GIS software and georeferenced using ArcGIS basemaps. The coordinate system used was World Geodetic System (WGS) 84 / Universal Transverse Mercator (UTM) zone 35N, since all of the area of interest in this paper is included in this UTM zone and it was considered inconvenient to use different coordinate systems for the areas included within the Greek and Turkish borders.

10The locus of interest was the NE Aegean area from the NW Anatolian coastline (Biga Peninsula or Troad, Turkey; Figure 1A) and the entrance to the Dardanelles Strait to the 135 m isobath, which is the maximum estimation of the RSL during the LGM followed in this paper (Lambeck et al., 2014). The border of the digitization followed the 140 m isobath, where the inclination of the sea floor was gentle, to the 200 m isobath in the north, along the NAT, and the southern part of the NE Aegean, where the depth increases abruptly. This was because when creating a DTM, the extent of the input datasets should be greater than the area of interest in order to increase the accuracy of extrapolations at the edges [http:// resources.arcgis.com/].

11The contours inside this sea area were digitized every 4 m between Lemnos, Ayios Efstratios, Imvros, Gallipoli Peninsula, Troad and Tenedos, and every 2 m until the 20 m isobath around the island of Lemnos. The digitized contours were then used to produce bathymetric DTMs and Triangulated Irregular Networks (TIN) of the sea area of the NE Aegean. For the islands and the coastal area bordering this region, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Model Version 2 (GDEM V2) was accessed from the publically available ASTGTM collection to obtain the land topography [hthttp://asterweb.jpl.nasa/ gov/gdem.asp]. The ASTER GDEM was cut upon the modern coastline of the area of interest, digitized from the ArcGIS satellite basemap on a scale of 1:5000 and superimposed on the bathymetric DTM as a separate layer1.

12For the purpose of this study, a series of maps was then created for six time intervals: the LGM (21st millennium BP; RSL -135 m, -130 m, -120 m), the Bølling-Allerød (ca. 14700-12800 BP; RSL at -100 m,-80 m), the Younger Dryas (ca. 12800-11600 BP; RSL at -60 m), the Early Holocene (10th millennium BP; RSL -40 m), the Early Neolithic (9th millennium BP; RSL at -20 m) and the Bronze Age (5th millennium BP; RSL at -4 m). The RSL is considered as a proxy for the coastline. The maximum expansion of the land area relative to the sea occurred during the LGM. The Bølling-Allerød was a period of climatic amelioration followed by rapid sea level rise, and it has been proposed that the first systematic attempts at sea voyages were made at this time (Ammerman, 2013). The Younger Dryas in particular is considered a major threshold, connected with the high mobility of forager-voyagers (Ammerman, 2014). The goal was to highlight the regression of the coastline during major climatic events and archaeological periods in the NE Aegean in order to better understand the evolution of the local maritime landscape and the challenges it posed for the prehistoric populations.

Results

13During the LGM lowstand (Figures 2A and 3A) Lemnos comprised the westernmost part of the Anatolian mainland. At that time, global sea-level is estimated to have been 135 m below the present level (Lambeck et al., 2014). Older publications regarding the Mediterranean region, however, suggest a RSL between 130-120 m below the present level for the NE Aegean (Perissoratis and Conispoliatis, 2003; Lambeck and Purcell, 2005). Throughout this period a large flat surface probably covered the Truva shelf. Lemnos was also connected to the island of Ayios Efstratios which formed a large southwest-facing peninsula. A distinctive geomorphological feature is the N-S-aligned valley on the northeastern side of the Truva shelf, defined by the 80 m depth contour, which extends from the Aegean Sea and runs parallel to the modern coast of the Gallipoli Peninsula. It is probable that the river Scamander (Karamenderes) extended across this plain onto the NE Aegean shelf during the last glacial and interglacial periods. Seismic data have shown that it emplaced deltaic deposits in the area (Gökaşan et al., 2010). A large open gulf formed the southward extension of this relatively flat plain, with two more confined coves to the east towards the Anatolian mainland. From a maritime perspective, these coves were very important as they constitute safe anchorages. During later periods, ships sailing up the coast of Asia Minor towards the Hellespont found it particularly difficult to round the Lekton promontory (the southwestern tip of the Troad) because of the strong winds encountered at the headland as they left the sheltered Adramyttion Bay south of the Troad (Morton, 2001). However, this would not have been the case during this sea-level lowstand.

14When RSL reached the 100 depth contour (Figure 3B), probably sometime around the beginning of the Bølling-Allerød interstadial, Lemnos was still connected to the Anatolian mainland. However, it was separated from Ayios Efstratios by a narrow channel of around 2 km width. The modern SW tip of the Troad, the ancient Lekton Promontory mentioned above, extended around 6 km to the west, forming the eastern side of a south-southwest facing embayment, and defined to the west by a moderately low peninsula.

15When the sea level reached the 80 m depth contour (Figure 3C) a narrow bay replaced the former Karamenderes valley. The Truva shelf was an extended catchment basin and it is possible that a large lake occupied its central part. This lake expanded rapidly and when the sea level reached the 76 m depth contour it was probably a lagoon, separated from the Aegean Sea to the south by a narrow isthmus less than 2 km wide. The area between the lagoon and the Karamenderes Gulf to the east-northeast was lowland of around 4 m elevation. With the rapid sea level rise it was probably progressively transformed into a swamp. At the 72 m depth contour a large well protected embayment, connected to the Aegean to the southwest by a narrow channel of less than 6 km width, occupied the central part of the Truva shelf. To the north, this embayment was blocked from the Aegean by a narrow isthmus that formed a land bridge connecting the unified Lemnos-Imvros Island with Anatolia. When the sea level reached the 68 m depth contour (ca. 13-12800 BP), this isthmus was submerged and Lemnos-Imvros constituted a large island separated from the Gallipoli Peninsula and Anatolia by a narrow NE-SW-facing channel. Shortly after, just before the Younger Dryas, there was an incursion of sea water from the Aegean into the Marmara Sea (McHugh et al., 2008).

16During the Younger Dryas (ca. 12800-11600 BP), Lemnos was still connected to Imvros by a land bridge the width of which was progressively decreasing (Figure 3D). However, the rate of sea-level rise was reduced throughout this period. It is noteworthy that the closest point connecting Lemnos to the mainland was not through Imvros, which was separated from the Gallipoli Peninsula by a ca. 15 km wide strait, but to a promontory forming the westward extension of Anatolia, around 30 km west from the modern coast- line of Tenedos. This promontory was separated from the east coast of Lemnos by a narrow strait 8-10 km wide, which formed the southward entrance to the Lemnos/Imvros – Anatolia channel.

17After the Younger Dryas, in the early years of the Holocene the rate of sea-level rise (Lambeck et al., 2014) increased, and when the sea level rose to the 40 m depth contour (ca. 10000 BP) Lemnos was separated from Imvros (Figure 4A). This process was probably completed in a relatively short length of time, given that when the sea level was at the -44 m depth contour the two islands were still attached, although by a very narrow land bridge. The distance between the two islands was of course much less than today and a small islet in the center of the strait, closer to Imvros, could be used as a stepping stone for the journey between them. The strait between Lemnos and Anatolia was widened to around 20 km.

18In the early Holocene, through the Mesolithic until the beginning of the Early Neolithic (10th- 8th millennium BP), the climate in the North Aegean was warm with mild and moist winters, except for short intervals of rapid climatic deterioration (Kuhnt et al., 2007, Gogou et al., 2007; Kotthoff et al., 2008). It is possible that the climate at this time was favor- able for navigation and the exploitation of maritime resources, hence the occurrence of coastal settlements. Another favorable factor is that the Aegean is characterized by enhanced productivity and is described as a mesotrophic sea (Kuhnt et al., 2007, Gogou et al., 2007). The sea level was rising continuously and rapidly from around -40 m at 10 ka BP to -20 m at 8.2 ka BP when a Rapid Climate Change occurred (Lambeck et al., 2014; Figure 2A and 4 B). To date, there are no known settlements on Lemnos dating from this period. With the onset of the Early Neolithic (9th millennium BP), and with a RSL around the 20 m depth contour, the shape of the coastline was generally very similar to the present day. An exception to this trend is the eastern coastline of Lemnos which extended towards the east. A long promontory which gradually became an island occupied the eastward extension of this coastline (Figure 4C). During the 5th millennium BP (Early Bronze Age) the RSL is estimated to have been at about 4-5 m below the present level (Pavlopoulos et al., 2013; Vacchi et al., 2014). The former eastern coastline of Lemnos was to a great extent inundated and a promontory appeared to exist to the east of the Alyki embayment (Figure 4D).

19According to Lambeck et al. (2014), between 8.2 ka BP and 2.5 ka BP there was a progressive decrease in the rate of sea level rise, after which ocean volumes remained nearly constant until 100-150 years ago, when a renewed sea level rise was initiated. From a more localized perspective, however, even small fluctuations in sea level can greatly alter the palaeogeography of the coastal zone, thus distorting our view regarding important features of the maritime landscape, such as safe anchorages, good fishing grounds, marine mollusc habitats, etc. This is particularly true for Lemnos where the depths are relatively shallow, and the 2 m depth contour was in some places as far as 300-500 m inshore from the modern coast- line. The implications of this are clearly evident. In the bay of Thanos, on the SW side of the island near the prehistoric site of Stvi, an underwater harbor structure of a much later date has been identified. Today it is located at a very shallow depth of around 0.5 m (Agallopoulou, 1994; Chalkioti, 2013; Figures 5C and 5D). Holocene alluvial deposits are documented in extensive areas, especially in the eastern and southern part of Lemnos, constituting an additional control on the shape of the coastline, especially at times when the rate of sea level rise was low. For this reason in areas of deep alluvial deposits bathymetric data alone may not in itself provide a reliable reconstruction. Future boreholes drilled in selected shallows, particularly on the east side of Lemnos, may provide valuable information about the evolution of the coastline and the role of sedimentation, as well as its origin.

Conclusions

20The maps presented here provide information about the time when the island of Lemnos was first separated from the mainland; its connection to neigh- boring islands, mainly to Imvros, during different time periods; the possible early corridors through which the island was colonized; and changes over time of the maritime landscape between Lemnos, Imvros and the northwest coast of Turkey. At a second level this study provides indications of promising areas for future work, such as the likely location of productive fisheries: e.g. the narrow inlets connecting large bodies of water, between small islands and the mainland, the tips of a headlands, and stream mouths. This approach has been used in Danish underwater surveys (Benjamin, 2010). With the aid of GIS and with reference to relevant data we can refine the above layers of investigation for particular time intervals. It is apparent that the environment of Palaeolithic and to a lesser extent Mesolithic populations in the NE Aegean was completely different to the present day – not only in terms of topography, but also in terms of climate, vegetation and maritime conditions. All of these parameters would have influenced human interaction with the maritime landscape. At the end of the Pleistocene in particular the existence of the large unified Lemnos-Imvros Island would have been a major environmental feature of the region and the strait between the island and the Anatolian main- land would have favored the existence of flourishing coastal sites on both sides. However, in order to test this hypothesis and to evaluate the evolution of the strait, extensive underwater surveys within the depth range of 40-80 m are necessary. However, it is possible to delineate more localized areas which are potentially promising for future geoarchaeological research, particularly in the shallows east of Lemnos and on the former land-bridge which connected it to Imvros.

Acknowledgments

21I would like to thank Nikolao Efstratiou, Professor of Prehistoric Archaeology in the Aristoteleio University of Thessaloniki, for giving me the idea of reconstructing the prehistoric coastlines of Lemnos and for assisting me with articles, photographs and valuable insights.