Strontium isotope variation and carbonate versus silicate weathering in rivers from across Alaska: Implications for provenance studies

The characterization of strontium (Sr) isotopic (87Sr/86Sr) variation in surface waters of Alaska (AK) has significant implications for provenance studies aiming to track movement patterns of animals. This study presents 87Sr/86Sr ratios, concentrations of Sr, Ca, Mg, Na and K, and selected molar ratios (Sr/Na, Ca/Na, Mg/Na and Ca/Sr) from 61 rivers from across AK to characterize regional patterns in i) 87Sr/86Sr variation and ii) carbonate versus silicate weathering influencing 87Sr/86Sr ratios. 87Sr/86Sr ratios range from 0.70422–0.74041±0.00009. Rivers north of the Denali Fault exhibit more radiogenic and variable 87Sr/86Sr ratios (0.70763 to 0.74041) than rivers to the south (0.70422 to 0.70895), reflecting the tectonic growth of southern AK via accretion of relatively young mafic-rich exotic island arcs along North America's continental margin during the Mesozoic. Within interior AK an east–west gradient exists. Radiogenic 87Sr/86Sr ratios (>0.725) in east-central AK and relatively low ratios (