Aim Salt‐marsh foraminifera are widely used as robust sea‐level indicators. High‐resolution Holocene sea‐level reconstructions depend on the accurate characterization of modern foraminifera‐environment relationships representative of a study site. We investigate the relationship between modern foraminiferal assemblage distribution and key environmental variables, viz. elevation above land levelling datum (LLD), sediment grain size, organic content, pH and salinity. We hypothesize that the distribution of modern salt‐marsh foraminifera is primarily controlled by elevation above LLD. Location Knysna and Keiskamma estuaries along the southern coastline of South Africa. Methods Salt‐marsh surface sediment samples (n = 97) were collected along eight intertidal transects with corresponding environmental data (pH, salinity, organic content, sand, silt, clay and elevation). Multivariate ordination analysis (partial redundancy analysis; pRDA) was used to investigate the relationship between living foraminiferal assemblages and environmental controls, after accounting for spatial variability in community composition. Results The pRDA suggests that species composition varied spatially within estuaries, but was strongly influenced by elevation at Keiskamma (r = 0.63) and Knysna (r = −0.75). At Keiskamma, the main gradient in composition was also influenced by salinity (r = −0.63), in an equal and opposite manner to elevation. Composition at Keiskamma was influenced to a much lesser extent by sediment organic content (r = 0.20) and the clay fraction (r = −0.13). At Knysna, pH (r = 0.455) was a secondary determinant of composition, and sediment characteristics covaried with elevation. Main conclusion Elevation was found to be a key environmental variable controlling the distribution of salt‐marsh foraminifera at both estuaries, thereby validating the use of foraminifera as sea‐level indicators. Certain species were particularly sensitive to elevation changes and could thus serve as useful indicators of past sea‐level change. This is an important first step towards the development of high‐resolution sea‐level reconstructions for the South African coastline.
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.
Salt-marsh foraminifera are used as precise sea-level change indicators as surface assemblages vary in relation to their position in the tidal frame. Surface-sediment samples were collected across an elevation gradient at Galpins salt marsh, South Africa, to study the vertical distribution of foraminifera and their potential use for sea-level studies. The marsh is divided into three vertical zones (high marsh, middle marsh, and mud flats) represented by three assemblage groups, with agglutinated species restricted to the upper reaches of the marsh and calcareous species more dominant towards the intertidal channel. The high marsh area is dominated by Jadammina macrescens with a presence of Trochammina inflata. The middle marsh is characterised by both T. inflata and Miliammina fusca. Calcareous species found in the mud flats consist of Haynesina germanica, Ammonia batava, and Quinqueloculina sp. This paper describes how marsh foraminifera can be used to define small-scale vertical zones along modern marsh surfaces and how these zones correspond to floral zones. We demonstrate that marsh foraminifera have potential to be used as precise indicators for sea-level reconstructions in South Africa.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.