A 30.5 m sediment core was recovered from the coastal lake Eilandvlei (EV13), which represents a unique high-resolution record of environmental change for southern Africa. For the establishment of a robust chronology, special emphasis was placed on the calibration of radiocarbon (14C) ages obtained from the dating of different material. However, the reliability of 14C ages can be problematic since coastal lakes interact with different source pools providing 14C-depleted (“old”) carbon thus causing reservoir effects. The origin of old carbon affecting the EV13 samples was most likely sourced from the Indian Ocean. Two pre-bomb marine molluscan shells were therefore analysed to determine the regional marine reservoir offset (ΔR), with obtained ΔR values of 134 ± 38 and 161 ± 38 14C yrs providing the first available data for the south coast of South Africa. However, the application of the resulting average ΔRmean = 148 ± 27 14C yrs for the calibration of the entire EV13 record underestimates the variable reservoir effects throughout the Holocene. These were possibly caused by past changes in the connectivity between the present lake system and the ocean as well as a varying degree of upwelling in this area. To solve this problem, three sample pairs (each consisting of wood fragments and bulk organic sediment from the same core depth) were dated to calculate the variable past reservoir effects. This approach provided a median basal age of 8920 +200/-250 cal BP. Palaeomagnetic secular variation stratigraphy was used to corroborate the chronology for the topmost 1.5 m of the record (past millennium), thus providing the first Holocene sediment based inclination and declination data from South Africa.
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FunderThis study was funded by the German Federal Ministry of Education and Research (BMBF). The investigations were conducted within the collaborative project “Regional Archives for Integrated Investigations” (RAIN), which is embedded in the international research programme SPACES (Science Partnership for the Assessment of Complex Earth System Processes).
- Coastal lake sediments
- Radiocarbon dating
- Marine reservoir effect
- Agulhas Bank
- Pre-bomb shells
- Palaeomagnetic secular variations