Tracing the Source of the Elephant And Hippopotamus Ivory from ...

Nevertheless, some caution must be used in interpreting strontium isotope data,
since, depending on the area, the strontium isotope values may vary locally between the
bedrock, sediment, and water, and Sr ratios of skeletal components (bone, dentine,
enamel) may vary as well (Price et al. 2002: 119). Moreover, “biologically available
strontium”, that is, strontium circulating in the natural environment, may be different
from geological strontium due to atmospheric sources of strontium (aeolian and
precipitation) and differential mineral weathering of rocks (Price et al. 2002: 119-120;
citing Chadwick et al. 1999; Miller et al. 1993; Graustein and Armstrong 1983). Price et
al. 2002: 119) resolves these problems by offering that “the impacts of such atmospheric
contributions are probably minimal in most areas, and particularly in much of
prehistory.”
More insights into specifics of strontium in the environment include the
following: a) alluvial sediments generally have 87 Sr/ 86 Sr values that are averaged from the
geological sources; b) plants growing close to rivers will have Sr values close to the value
of the river water, while those not close to rivers will have Sr values of the soil, and the
same goes for the animals eating these plants; c) the Sr value of plants is distinct from
bedrock values; and d) surface water may have a lower Sr ratio than the surrounding
plants and soils (Price et al. 2002: 120-121, citing Sillen et al. 1998). Thus the one to one
relationship of strontium values between bedrock geology, sediments, plants, and water
has been dismissed, which shifts the emphasis to a “biologically available strontium”
approach when employing strontium isotopes. Luckily animal skeletal tissues serve as an
averaging mechanism for the potentially heterogeneous strontium values available in the
87