Browsing by Subject "carbon isotopes"

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    Open Access
    Exploring high-resolution carbon isotopes in archaeological charcoal as a rainfall seasonality proxy
    (2025) Poretti, Gemma Dimitra; Hare, Vincent
    Rainfall in present-day South Africa is distinctly seasonal, with a Summer Rainfall Zone (SRZ) in the east, a Winter Rainfall Zone (WRZ) in the west, and a Year-Round Rainfall Zone (YRZ) along the south coast and interior between them. Understanding shifts in these zones during Late Pleistocene glacial- interglacial cycles is crucial for both regional climate reconstructions and interpreting behavioural variability in the South African Later Stone Age (LSA) archaeological record. However, several key palaeoarchives employed to reconstruct rainfall seasonality during the Late Pleistocene are hindered by low temporal resolution, reliance on inference and untenable ecological relationships, and their spatial and temporal distance from archaeological evidence. This research tests whether a proven seasonal precipitation proxy (SPP) based on high-resolution carbon isotope profiles — successfully applied to evergreen wood in the Northern Hemisphere — can be used to reconstruct rainfall seasonality from South African archaeological Proteaceae (angiosperm) and Podocarpaceae (gymnosperm) charcoal. Modern Protea and Podocarpus wood and charcoal samples from all three rainfall zones are tested to assess the SPP's applicability in South Africa and its ability to extract seasonal climate data from different materials. Results show that seasonal amplitudes (Δδ13Cmeas), changes in precipitation (ΔP), and ratios of summer to winter rainfall (PS/PW) align with local rainfall data. Slight discrepancies between wood and charcoal seasonal amplitudes and therefore values for ΔP and PS/PW are attributed to carbonisation effects, including 13C depletion and volume shrinkage leading to reduced sampling resolution, which lead to a repeated but quantifiable overestimation of summer rainfall in charcoal. In the WRZ, seasonal amplitudes are dulled relative to local rainfall data due to intermittent growth cessation during seasonal dry periods, but these effects could in some cases be corrected for. Analysis of Podocarpaceae charcoals from Waterfall Bluff showed an increase in summer rainfall during the Last Glacial-Interglacial Transition (LGIT), while Proteaceae charcoals from Boomplaas Cave showed an increase in winter rainfall during the Last Glacial Maximum (LGM). These results support existing models of Southern Hemisphere (SH) westerly shifts. The SPP offers a quantitative, high-resolution, on-site proxy for seasonality in archaeological contexts, with potential applicability to global archaeological sites from which evergreen charcoals have been retrieved.
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    Open Access
    Isotopic ecology of fossil fauna from Olduvai Gorge at ca 1.8 Ma, compared with modern fauna
    (2013) van der Merwe, Nikolaas J
    Light stable isotope ratios (δ13C and δ18O) of tooth enamel have been widely used to determine the diets and water sources of fossil fauna. The carbon isotope ratios indicate whether the plants at the base of the food web used C3 or C4 photosynthetic pathways, while the oxygen isotope ratios indicate the composition of the local rainfall and whether the animals drank water or obtained it from plants. The contrasting diets of two early hominin species – Homo habilis and Paranthropus boisei – of ca 1.8 Ma (million years ago) in Tanzania were determined by means of stable carbon isotope analysis of their tooth enamel in a previous study. The diets of two specimens of P. boisei, from Olduvai and Peninj, proved to be particularly unusual, because 80% of their carbon was derived from C4 plants. It was suggested that their diet consisted primarily of plants, with particular emphasis on papyrus, a C4sedge. The dominance of C4 plants in the diet of P. boisei is a finding supported in another study of 22 specimens from Kenya. The isotopic ecology and diets of fossil fauna that were present at the same time as the two fossil hominin species are described here, in order to provide a fuller understanding of their contrasting diets and of the moisture sources of their water intake. This information was then compared with the isotopic composition of modern fauna from the same region of Tanzania. The carbon isotope ratios for both fossil and modern specimens show that the habitats in which these faunal populations lived were quite similar – grassland or wooded grassland. They had enough bushes and trees to support a few species of browsers, but most of the animals were grazers or mixed feeders. The oxygen isotope ratios of the fossil and modern fauna were, however, very different, suggesting strongly that the source of moisture for the rain in the Olduvai region has changed during the past 1.8 million years.