TRACING DUST PROVENANCE, CYCLING, AND HISTORY IN THE WASATCH MOUNTAINS USING STRONTIUM ISOTOPES AND TREE RINGS

Dust cycling from the Great Basin to the Rocky Mountains is an important component of ecological and hydrological processes. We have investigated the use of strontium concentrations and isotopes (⁸⁷Sr/⁸⁶Sr) to trace dust provenance in the Wasatch Mountains and to determine whether or not this tracer signal is preserved in tree rings. We measured the strontium isotope signatures of dust landing on the Wasatch Mountains, soil, bedrock, and tree rings. Over 94% of strontium in soil over quartzite, 62% of strontium in soil over granodiorite, and 71% of strontium in soil over limestone, is from dust. Over 85% of strontium in trees growing over quartzite, 54% of strontium in trees growing over granodiorite, and between 24% and 97% of strontium in trees growing over limestone, is from dust. The tree ring isotopic signature is a reflection of how strontium from dust and bedrock mix within the soil. This can then be used to trace changes in dust sources through time via tree rings. A large fraction of the strontium in soil and tree rings comes from dust, although some bedrock dependent variation exists. Trees get a majority of their strontium from dust, making them a useful record of dust source and deposition. Over time, a tree growing over the Tintic Quartzite shows changes in strontium source, which are interpreted as changes in dust source.