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 sea- level 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.