Strontium ratios in rocks vary depending on the type of rock and the rock's age. The continental-scale water model previously developed by researchers at the University of Utah, uses bedrock geology and all major river systems and drainages to predict strontium isotope ratios (the ratio of strontium 87 to strontium 86) in surface waters. These applications of strontium isotope analysis are focused on quantifying weathering rates for minerals and rocks, and the sources and fates of strontium in rivers.
Tracking strontium isotope ratios is a valuable tool beyond the science described above. The heavy metal strontium can be found in most organic substances such as bones, teeth, soils and plant tissues. As a result, strontium isotope ratios are used in fields including forensics research, animal poaching investigations, and even tracking where marijuana plants came from in drug busts.
Research, led by colleagues at the University of Cincinnati, used the above mentioned water model to compare predicted strontium isotope ratios in surface water, soil, vegetation, fish and mammal skeletal tissues from a massive collection of data across the U.S., excluding Alaska and Hawaii.
Because the ratio of strontium 87 to strontium 86 in water, soil, vegetation and animal tissues predominantly reflect local geology, they can be used to distinguish geologically distinct regions as well as identify highly mobile populations. We tested how accurate the model was at predicting strontium ratios not just in water, but in additional materials relevant to ecological and paleoecological research.
Although strontium isotope analysis related to biological research is certainly on the rise, the expense in terms of ground mapping has so far been prohibitive.
It's a really powerful system, but in order to get an idea of where elephant tusks confiscated in Kenya came from, for example, investigators would have to track the strontium signals throughout the country or potentially all over East Africa. Models like the one we tested could make it possible to quickly get a good idea of where that animal was originally from.
The researchers say the water model provides a readily available source of background data for predicting strontium ratios for biologically relevant materials in regions where empirical data are lacking. The availability of increasingly high-quality modeled strontium data will dramatically expand the accessibility of this geochemical tool to ecological applications.