Introducing a terrestrial carbon pool in warm desert bedrock mountains, southwestern USA

Growth of the Phoenix metropolitan area led to road cut or house platform exposures of the internal bedrock material of surrounding semiarid mountain ranges. Similar exposures in the surrounding Sonoran and Mojave Deserts reveal the presence of sedimentary calcium carbonate infilling the preexisting fracture matrix of the bedrock. Field surveys at 31 sites with bedrock fractures filled with carbonate, referred to as BFFC in the following text, reveal an average of 0.079 ± 0.036 mTC/m² stored in the upper 2 m of analyzed bedrock exposures. Backscattered electron microscopy images indicate the presence of carbonate at the micron scale, not included in this estimate of carbon storage. Pilot radiocarbon and Sr isotope analyses suggest that one of the surveyed BFFC veins was flushed into the bedrock from a nonbedrock source during the wetter last glacial period in the late Pleistocene.