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).