Browsing by Author "Van der Merwe, Nikolaas"

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    A holocene sea surface temperature record in mollusc shells from the South African coast
    (1993) Cohen, Anne Louise; Van der Merwe, Nikolaas; Branch, George
    This thesis describes the construction of a Holocene history of sea surface temperatures in coastal regions of the southern Benguela and eastern Agulhas Bank of South Africa, using marine mollusc shells preserved in archaeological middens. Two independent palaeothermometers were employed: the traditional oxygen isotope technique and a new, alternative technique based on temperature-dependent changes in structure and mineralogy of the shell of a South African limpet species, Patella granularis. The relationship between the isotopic and structural aspects of shell composition, and habitat temperature was confirmed through examination of living populations.
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    Stable carbon isotopes in deep time : the diets of fossil fauna and hominids
    (1989) Lee-Thorp, Julia Anne; Van der Merwe, Nikolaas
    This thesis describes the development, testing and application of a technique for extending carbon isotopic dietary tracing millions of years in time,. using the mineral phase of calcified tissues (apatite) as alternative sample material to collagen. The results reported here provide empirical evidence for the validity of the technique. Investigation of the isotopic relationships between diet, collagen and apatite, using a large sample of modem fauna with known diets, confirms that the isotopic relationship between collagen and apatite changes with trophic level.
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    The use of stable isotope ratios of carbon and nitrogen to elucidate pelagic marine foodwebs of the Benguela and Agulhas Bank regions of South Africa
    (1992) Sholto-Douglas, A D; Field, John G; Van der Merwe, Nikolaas
    Isotope assessments of foodweb relationships amongst pelagic organisms may be influenced by their lipid content, since lipids are more depleted in ¹³C than other biochemical compounds. This is particularly important for plankton which show a greater decrease in δ¹³C caused by the failure to remove lipids during sample preparation, than the muscle tissue of pelagic fish species. Lipid removal is important for those fish species whose lipid content and magnitude of diet-consumer fractionation are simultaneously related to their size. The period required for pelagic fish to isotopically reflect a new diet is slow, of the order of months and years, and may depend on the diet and the magnitude of isotopic change displayed. It is likely that this rate decreases as the fish approach isotopic equilibrium with the new food source.