Introduction
Earth is currently in the grip of the Quaternary glaciation, where climate alternates between cold temperature intervals, called glacial periods, and phases of warmer climate, called interglacial periods. Glacial-interglacial cycles have waxed and waned throughout the Quaternary Period (the past 2.6 million years) and are believed to be driven by changes in the orbital pattern of the Earth that has periods of about 20 000, 40 000 and 100 000 years. An interglacial period is characterised by relatively warm climates, transgressive sea levels and reduced ice cover. In contrast, lower temperatures, glacier growth and the development of continental ice sheets generally define a glacial period.
We are living in the Holocene Interglacial period, which broadly covers the last 10 000 years. Archaeological sites on the southern shores of South Africa hold some of the world’s richest records of early modern humans, spanning several glacial and interglacial periods (Deacon and Deacon 1999; Mitchell 2002). So, how did these climate fluctuations affect the position and nature of South Africa’s coastlines? Sedimentological and micropalaeontological studies, seismic-profiling surveys, as well as archaeological investigations have helped clarify the history of sea level movements along southern Cape coast (Siesser and Dingle 1981; Cawthra et al. 2020a, 2020b). Most of the archaeological records come from caves that now look out on to the sea, with many sites situated only metres away from the shore (Figure 1). However, throughout most of the last 200 000 years, these caves were under water, while at other times they were kilometres from the coast (Davies 1972). Two scenarios demonstrate the effect of glacial and interglacial phases.
False Bay, Cape Town
Imagine standing on top of Table Mountain around 125 000 years before the present. This was a time characterized by rising sea levels known as the Last Interglacial Period, when temperatures in the Arctic region were about 2-4 °C higher than today. With global sea levels peaking at around 8 m higher than present, the False and Table Bay coastlines were inundated and the Cape Flats totally submerged, while Table Mountain and the Cape Point promontory formed two separate islands (Figure 2).
The southwestern Cape coast
Movies like Ice Age popularized the phenomenon of extreme climate changes in the past when massive ice sheets and glaciers covered the northern hemisphere. The last cold phase, known as the Last Glacial Period, began about 115,000 years ago and ended around 15,000 years ago. This was also a time when South Africa was well and truly affected by colder climates. However, while no glaciers or continental ice sheets occurred here, lowering sea levels exposed large tracts of land around the country’s coastline (Dingle and Rogers 1972).
Now, imagine standing in a cave facing the sea near Mossel Bay or Plettenberg Bay in the Western Cape, and looking south. All you see are rolling grasslands stretching for kilometres into the distance (Figure 3). This scenario would have played itself out around 20 000 years ago, when an extreme drop in global temperatures during an episode known as the Last Glacial Maximum culminated in the build-up of polar ice. This ice formation ‘locked up’ huge volumes of sea water and exposed parts of South Africa’s continental shelf known as the Palaeo-Agulhas Plain (Cawthra 2020a, 2020b; Cowling et al. 2020) (Figure 4). Generations of humans occupying this cave over a period dating from 110 000 years to 15 000 years ago, would have witnessed a retreating coastline that was at some time as much as 120 km distant (Marean et al 2020). This worldwide change in sea level exposed up to 80 000 km2 of previously submerged land off the southern African coast, forming large tracts of relatively fertile, low-lying land and so forming a unique coastal plain environment covered by extensive grasslands, and so forming a unique coastal plain environment for grazing mammals that preferred open country vegetation (Dingle and Rogers 1972; Rossouw 2001). Extinct giant buffalo, giant wildebeest-like antelopes, and giant zebras, along with quagga, springbok, bontebok, wildebeest, hartebeest and a range of carnivores, would have roamed these grasslands (Venter et al. 2020). In addition to being a highly productive grassland ecosystem with a large diversity of grazer species available for hunting, the Palaeo-Agulhas Plain also provided access to a resource-rich coastline, which would have made it a prime foraging habitat for early modern humans (Marean et al. 2020).
The Palaeo-Agulhas Plain was rapidly submerged around 11 000 years ago with the advent of the Holocene Interglacial Period when global ice sheets melted, moving the coastline’s position back to where it is today (Deacon and Lancaster 1988).
References
Cawthra, H.C., et al., 2020a. Migration of Pleistocene shorelines across the Palaeo-Agulhas Plain: Evidence from dated sub-bottom profiles and archaeological shellfish assemblages. Quaternary Science Reviews, Vol. 235.
Cawthra, H.C., et al., 2020b. Geological and soil maps of the Palaeo-Agulhas Plain for the Last Glacial Maximum. Quaternary Science Reviews, Vol. 235.
Cowling R. M., et al., 2020. Describing a drowned Pleistocene ecosystem: Last Glacial Maximum vegetation reconstruction of the Palaeo-Agulhas Plain. Quaternary Science Reviews, Vol. 235.
Davies, O. 1971. Pleistocene shorelines in the southern and south-eastern Cape Province (Part 2). Annals of the Natal Museum 21(2): 225 – 279.
Deacon, H.J. and Deacon J. 1999. Human Beginnings in South Africa: Uncovering the Secrets of the Stone Age. Altamira Press. Walnut Creek, California 214 pp.
Deacon, J. and Lancaster, N. 1988. Late Quaternary Palaeoenvironments of Southern Africa. Oxford University Press, Oxford, 225 pp.
Dingle, R.V. & Rogers J. 1972. Pleistocene Palaeogeography of the Agulhas Bank. Transactions of the Royal Society of South Africa. Vol. 40(3).
Marean, C.W., et al., 2020. The Palaeo-Agulhas Plain: temporal and spatial variation in an extraordinary extinct Pleistocene ecosystem of the greater cape Floristic region. Quaternary Science Reviews, Vol. 235.
Mitchell, P. The Archaeology of Southern Africa. Cambridge Universty Press. Cambridge 515pp.
Rossouw, L. 2001. The status and palaeoecology of the extinct Southern Springbok, Antidorcas australis, as reflected by its postcranial osteomorphology. Unpublished MSc. thesis, Bernard Price Institute for Palaeontology, University of the Witwatersrand.
Sealy, J. et al. 2020. Climate and ecology of the Palaeo-Agulhas Plain from stable carbon and oxygen isotopes in bovid tooth enamel from Nelson Bay Cave, South Africa. Quaternary Science Reviews, Vol. 235.
Siesser W.G. and Dingle, R.V. 1981. Tertiary Sea-Level Movements around Southern Africa. The Journal of Geology 89(1) 83 – 96.
Venter J.A., et al., 2020. Large mammals of the Palaeo-Agulhas Plain showed resilience to extreme climate change but vulnerability to modern human impacts. Quaternary Science Reviews, Vol. 235.
Figure Captions
Figure 1. Cave sites with some of the richest records of early modern human occupation along the southern Cape coast: Pinnacle Point near Mossel Bay (left) and Nelson Bay Cave near Plettenberg Bay (above right). Photograph of excavated cave deposits with well-preserved and finely stratified layers, yielding cultural remains left behind by early modern humans (below right). Photographs provided by L Rossouw.
Figure 2. Google Earth aerial photograph modified to show modern False bay coastline (left) and effects of raised sea levels on False Bay and the Cape Flats around 125 000 years ago (right).
Figure 3. Looking out at the Palaeo-Agulhas Plain from a cave entrance at the Pinnacle Point (left) and the same view today where the ocean is within meters of the cave entrance (right). Photographs provided and adapted by L. Rossouw.
Figure 4. Google Earth map of southernmost Africa showing the submerged Palaeo-Agulhas Plain in navy blue. The dashed red line indicates the – 120 km coastline during the Last Glacial Maximum around 18 000 years ago (after Deacon and Lancaster 1988 and Sealy et al. 2019).
Comments are closed.