Using strontium isotopes to trace dust from a drying Great Salt Lake to adjacent urban areas and mountain snowpack

With the desiccation of saline lakes around the globe, it is increasingly important to quantify the impacts of playa dust on downwind urban areas and mountain snowpack. In this study, we used Sr-87/Sr-86 ratios of carbonate minerals to trace dust from playas to urban areas and mountain snowpack. We focused on dust contributions from Great Salt Lake (GSL), in northern Utah, USA, which recently reached historic lows in water levels exposing large areas of dry lakebed. We measured Sr-87/Sr-86 ratios in dust from GSL, Sevier Dry Lake (SDL), and other playas across western Utah and compared them to Sr-87/Sr-86 ratios in dust across the urban Wasatch Front and mountain snowpack collected seasonally from 2015-2018. Dust from GSL had unique Sr-87/Sr-86 ratios (similar to 0.715) relative to SDL (similar to 0.710) and other playas (similar to 0.711 to 0.712), providing a potentially powerful tool for tracing GSL dust to downwind areas. Dust deposition had Sr-87/Sr-86 ratios ranging from similar to 0.710 to similar to 0.712 in the urban area and snowpack, within the range of playa dust sources. Using a simple two-endmember mixing model considering only GSL and SDL as sources, GSL contributed 5% of the dust flux to the southern Wasatch Front (Provo) and between 30%-34% of the dust flux to the northern Wasatch Front (Salt Lake City, Ogden, and Logan). For mountain snowpack, GSL contributed 11% of the dust flux to the Uinta Mountains and 22% of the dust flux to the Wasatch Mountains. Dust transport modeling could be combined with Sr-87/Sr-86 fingerprints for source apportionment in northern Utah and other areas that are impacted by regional playa dust.