Sea levels have varied throughout time, alternating between advancing and declining across coastal plains. During the Quaternary period, sea levels change because of the cyclic growth and deterioration of ice sheets. Relative positions of sea and land surfaces are indicators, since, they provide evidence on the volume of the ocean and vertical movements of the land. One of the main contributing factors to the changes in sea levels currently is the last glacial maximum. During, this period vast volumes of water was frozen and transformed into ice sheets. Thus, sea levels were 100-150 m (meters) lower, when compared to sea levels today (fig 1).
Therefore, huge areas across the coastal pains would have been exposed and available for human activities. Since the Late Palaeolithic period, sea levels have drastically risen because of the ice-sheets covering North America and northern Europe has been melting away. These ice-sheets covered a massive area and contained a considerable volume of water that, when this occurred, sea level rose worldwide ranging from 120-130 m. This process began around 18,000 years before present. Thus, having enormous effects on the prehistoric archaeological records for human movement and settlements within this period, since, the exposed areas are now currently flooded and submerged underwater (Lambeck, 1996).
Figure 1. Coastal palaeogeography of southern South Africa (black is exposed land). (Van Andel, 1989).
The low sea level of the last glacial maximum period uncovered extensive coastal plains globally, most of the new regions were all fairly level, allowing for ease of access and travel.
In addition, it was also able to connect different regions together because of land-bridges that formed between continents or between mainland and islands. For example, the land-bridge connected Europe and the British Isles together. In other cases, such as North-western Australia and Indonesia, the distance across the sea between the two countries was hugely reduced. Archaeologists have been able to analyse the changes in coastal palaeogeography and use evidence that has been excavated, to answer questions about migrations of past hunter-gatherer groups (Van Andel, 1989).
In order, for us to be able to fully understand our past settlements and migration patterns in correlation to the effects of Pleistocene sea level change on our environment, prehistoric coastal archaeological records play a vital role. Isostatic, eustatic and tectonic processes are critical for sea level changes as, these three processes provide an insight into to when and how coastal landscapes and archaeology formed during periods of lowered sea level. Within, this period optimum geomorphological conditions are required for the preservation of archaeological and palaeoenvironmental data. One of the main implications of the last maximum glacial is subducting coastlines. Tectonic uplift of coastlines, by subduction and under-thrusting. The main issues with this are that sites that were above sea level in the past are now submerged underwater (fig 2), (Bailey and Flemming, 2008).
Archaeologist have been able to make predictions of where the shorelines would have been located during the last glacial maximum, records have been published for both global and regional reconstructions. For example, in Greece, they have a late Palaeolithic strata of Franchthi cave. Unusually, in this sites no fish bones were excavated, from the predictions of the shorelines, it is now believed that the reason for a lack of fish bones is due to the shoreline being located away, rather than their fishing skills not being adequate (Lambeck and Chappell, 2001).Mesolithic Settlement coastal site at Howick, NorthumberlandThe archaeological site of Howick is located North-east at the coast of Northumberland, England. Excavation took place on the site during the period of 2000 – 2002, revealing evidence for a prehistoric Mesolithic settlement. With the use of radiocarbon dating its believed to be earlier eighth millennium, making it one of the earliest known Mesolithic site in northern Britain. Furthermore, archaeologist were able to recover an 8m core of sediment, giving them an inside into to the local environmental conditions. Therefore, this site is able to provide information to further our understanding of hunter-gatherer settlements throughout a period that consisted of heavy paleogeography change (Waddington et al., 2003). Within, the site archaeologist were able to excavate and identify the main feature, which consisted of a circular structure, that averaged around 6m in diameter. The structure was situated halfway alongside the erosion scar, which was located next to the edge of the trench. The structure contained; pits, post holes, stake holes, linear slots, and a series of hearths deposits. Furthermore, material remains such as flint, ochre and charred organic residues of fragments of bone, hazelnuts and acorn shells, was found. In addition, the presence of birds, wild pigs, foxes and either a wolf or dog were found within the hearths, by analysing the burnt bones excavated. With the evidence, available from the site, the archaeologist was able to identify the occupation of the site as semi-permanent or permanent over a long duration of time. However, the eastern area of the site has been truncated because of erosion down the cliff edge. The bones were inadequately preserved and broken up into fragments, as a result of acidic pH levels of the soil and waterlogging (poor conditions for bones). When this Mesolithic site was occupied, it was during a period of lower sea level than present. Also, the shoreline during this phase it would had an increased distance to the coastal plain (Waddington et al., 2003). However, the sea level was rising rapidly as the deglaciation of the last glacial maximum was reaching its ending between 10,000 – 6,000 BP. This is indicated by the variation in eustatic sea level and data on the global ice volumes (Pirazzoli 1996). Late Mesolithic settlement at Tybrind Vig, Denmark This is a late Mesolithic coastal settlement, that dates to 5600 – 4000 BC, in Tybrind Vig, Denmark. The excavation of the site has revealed vital information about fishing activity, it is considered to be the best-preserved example from the Mesolithic in Europe. The site has also yielded food plant remains in the form of charred fragments of sea beet, acorn, and hazelnut. Furthermore, other edible plant seeds and fruits were discovered in the waterlogged remains, suggesting the possibility of a wider range of food plants within the area. Along the coastal zones of southern Scandinavia, is where the evidence for late Mesolithic settlements are located. The shallow, brackish lagoons, were created by repeated transgressions that occurred in the Atlantic period, was an ideal spot for late Mesolithic settlement. This site supported hunter-gatherer communities around 5600-4000 B.C. These settlements are located along a shoreline of the coast that is being protected by a cove, or shallow, brackish lagoon. However, due to the last maximum glacial and the rise in sea levels, this region of Denmark has sunk. Present day the late Mesolithic period settlement is located 250 m from the coastline and 3 m submerged underwater. The underwater excavation of this sites happened between 1978 – 1987. The project yielded mass amounts of finds for inshore fishing. Items such as; traps, hooks, leister prongs, dug-out canoes and paddles were all excavated and salvaged (Kubiak-Martens, 1999).This prehistoric submerged archaeological site is remarkable because of its ability to preserve organic materials in the marine environment. Thus, enabling archaeologist to give new insight on a range of technologies, that can’t be excavated on terrestrial records. These included cordage, woodworking, and weaving. Furthermore, this evidence suggests, the people that lived here during this period had a range of technological skills, knowledge of the local environment and material properties. Additionally, the preservation of these materials offer, further information on day-to-day practices such as fishing or food gathering. This is extremely valuable since; in the terrestrial record, it is very rare to find a signature for this type of activities. The melting of ice sheets and slow increase of sea level has caused the prehistoric coastal landscape, to bury settlements in an anaerobic environment for preservation. Therefore, artefacts such as; stone and wooden tools, log boats, human burials, decorated paddles, fishing equipment, textiles, charred food remains and bones were preserved. The amount of different log boat fragments discovered and the quality of the construction suggest that vast amount of time and resource were used to craft these log boats as it was used as a common form of transportation, along with fishing. Finally, the site also revealed an art style, which hadn’t been previously recorded in the archaeological records. The art varied from having a stamp that was created from a dark brown pigment, carvings, and geometric shapes with sinuous bands (Farr, 2015). Figure 2. Coastline uplifted by isostatic or tectonic movement, A shows land before uplift and B shows the land when the coastline is subducting. (Bailey and Flemming, 2008).Conclusion In conclusion, the implications of sea-level change since the last glacial maximum for the prehistoric archaeological record varies differently depending on which site you are analysing. The impacts of the last glacial maximum on the archaeological records are both positive and negative, it can be considered as a double-edged sword. To begin, on dry land, we are only able to gain a limited amount of knowledge about the people in the past, since, only certain artefacts are preserved such as chipped stone tools. The availability of well preserved prehistoric sites is quite rare. The implication of sea level rise meant that flat and level exposed land such as Tybrind Vig was submerged underwater. Due to the sites being waterlogged and submerged, it created ideal conditions that preserved organic material. Organic material is vital, as it provides an insight into to the daily lives of hunter-gatherers. Numerous amounts of prehistoric coastlines were flooded because of marine transgressions since the last Ice Age, therefore, it opens the world to the potential preservation of evidence of prehistoric activity within these now submerged landscapes. The submerged sites have the potential to be able to change our view of many aspects of prehistoric life.The negative of this implication is that even though it does help preserve organic material, the sites are submerged underwater, making it difficult to locate the exact location of the sites. Furthermore, visibility is reduced underwater and in cases such as the log boats in Tybrind Vig, they have been preserved very well, but the log boat has been flattened because of the weight of sediment and water. In an archaeological context, the most valuable aspect area being able to identify environmental changes that occurred over time due to sea levels.
Thus, the importance of these sites is extremely valuable as they provide information on past human settlements and migration patterns