A late Holocene sea-level curve for the east coast of South Africa

Abstract

South Africa's extensive and topographically diverse coastline lends itself to interpreting and understanding sea-level fluctuations through a range of geomorphological and biological proxies. In this paper, we present a high-resolution record of sea-level change for the past ~1200 years derived from foraminiferal analysis of a salt-marsh peat sequence at Kariega Estuary, South Africa. A 0.94-m salt-marsh peat core was extracted using a gouge auger, and chronologically constrained using five radiocarbon age determinations by accelerator mass spectrometry, which places the record within the late Holocene period. Fossil foraminifera were analysed at a high downcore resolution, and a transfer function was applied to produce a relative sealevel reconstruction. The reconstructed sea-level curve depicts a transgression prior to 1100 cal years BP which correlates with existing palaeoenvironmental literature from southern Africa. From ~1100 to ~300 cal years BP, sea levels oscillated (~0.5-m amplitudes) but remained consistently lower than present-day mean sea level. The lowest recorded sea level of −1±0.2 m was reached between 800 and 600 cal years BP. After 300 cal years BP, relative sea level has remained relatively stable. Based on the outcomes of this research, we suggest that intertidal salt-marsh foraminifera demonstrate potential for the high-resolution reconstruction of relative sea-level change along the southern African coastline.In the southern African context, the application of foraminifera as biological indicators has been restricted to studies of stratigraphy 26 , temperature change 27 , sedimentology [28][29][30][31] and marine records 32 . The use of salt-marsh foraminifera to reconstruct relative sea-level change has been limited to a single published study at Langebaan. 33 Here we introduce an established sea-level proxy to determine proof of concept for South African sea-level research. This technique has the potential to contribute to our incomplete understanding of past sea-level change along the southern African coastline. HOW TO CITE:Strachan KL, Finch JM, Hill T, Barnett RL. A late Holocene sea-level curve for the east coast of South Africa. S Afr J Sci. 2014;110(1/2), Art. #2013-0198, 9 pages. http://dx.

Vertical Zonation of Foraminifera Assemblages in Galpins Salt Marsh, South Africa

“…Modern foraminiferal training sets are applied to downcore fossilised assemblages via a transfer function to reconstruct palaeomarsh surface elevations and, thereby, relative sea level (e.g., Barlow et al, 2013;Strachan et al, 2014). Franceschini et al (2005) represent one of the few studies to successfully reconstruct relative sea level in South Africa using, in part, foraminifera.…”

“…It would be prudent, however, to investigate ecological controls on South African salt-marsh foraminifera prior to reconstruction attempts, as this area of research is severely lacking in the country. Combining floral and foraminiferal vertical zonation across salt marshes in South Africa may help to further reduce uncertainties in future studies concerned with relative sea-level reconstruction (Strachan et al, 2014).…”

“…Regression modelling of the modern training set suggests salt-marsh foraminifera are able to predict marsh surface elevations with a precision of 6 17 cm, comparable to published saltmarsh based sea-level studies. Sea-level research in South Africa should use the local resources available to provide high-precision and high-resolution reconstructions of recent sea-level change (e.g., Strachan et al, 2014), previously not applied in the country. Suitable salt marshes have been identified throughout the coastal zones of South Africa and further analysis of modern day microfaunal assemblages and subsurface litho-and biostratigraphies should be able to produce relative sea-level reconstructions comparable with those published worldwide.…”

“…The focus of this paper is to investigate the vertical distribution of modern foraminifera in a South African salt marsh to determine whether the assemblages show evidence of vertical zonation. This paper tests whether foraminifera from this marsh can accurately predict salt-marsh surface elevations (Strachan et al, 2014), and thereby sea level, with precisions comparable to that of published South African sea-level studies by Siesser (1974), Miller et al (1995), Marker (1997), Compton (2001), and Norstrom et al (2012). In addition, we investigate whether dead foraminiferal counts are more suitable for palaeo-reconstruction purposes than total counts.…”

“…In addition, we investigate whether dead foraminiferal counts are more suitable for palaeo-reconstruction purposes than total counts. The establishment of modern training sets of salt-marsh microfauna and a quantitative investigation of their relationship with elevation is an important first step towards the application of salt-marsh microorganisms to reconstruct former relative sea levels in South Africa (Strachan et al, 2014).…”