Animal Samples, Characteristics of Sampling Locality and Analytical Methods

ANIMAL SAMPLES, CHARACTERISTICS OF SAMPLING LOCALITY, AND ANALYTICAL METHODS 

Bone and tooth enamel from modem animals were collected in 1984 and 1993 from skeletons exposed on the surface in Sibiloi National Park, located on the east shore of Lake Turkana in northern Kenya. In addition to its interest as the site of numerous fossil hominid discoveries, the Turkana area provides an ideal controlled situation for the present study. The park is a circumscribed area surrounded by human pastoral groups and the nondomestic fauna remain to a great extent within its confines. Water sources are limited to the lake, ephemeral streams, a limited number of waterholes, and the plants eaten by the animals. The streams last on the order of days and in dry years do not flow at all. The non-domestic animals from which the bone and enamel were collected likely obtained most of their drinking water from the lake itself Domestic animals entered the park in 1984 during a severe drought. Their drinking water sources may have varied widely. 

The original method of phosphate preparation involved extracting the phosphate and reprecipitating it as a bismuth phosphate (Tudge 1960). Alternatively, it is precipitated as a silver phosphate (Wright and Hoering 1989) which involves fewer steps and, more importantly, silver phosphate is not hygroscopic (as is bismuth phosphate) which minimizes the potential for contamination by atmospheric water. 

A greater hindrance for paleoclimate studies, however, is that the traditional method required reduction in an all metal vacuum line at high temperature (in externally-heated nickel reaction vessels) with bromine pentafluoride (BrFs), a highly reactive gas (Clayton and Mayeda 1963). Handling this material in anything other than a dedicated geochemistry laboratory has proven extremely difficult and dangerous (Chivas 1984). 

Two alternate methods have recently been developed and both are used in the present study. A laser probe analytical method provided the majority of the oxygen isotope data (see Kohn et al. 1996 for details on testing and developing the method). Laser probes were originally developed for the stable isotope analysis of silicates, oxides, and sulfides in ciystalline rocks (Crowe 

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