A 4,500‐Year‐Long Record of Southern Rocky Mountain Dust Deposition

Dust emissions from southwestern North America (Southwest) impact human health and water resources. Whereas a growing network of regional dust reconstructions characterizes the long‐term natural variability of dustiness in the Southwest, short‐term fluctuations remain unexplored. We present a 4.5‐millennia near‐annual record of dust mass accumulation rates from the southern Rocky Mountains, CO. Using microscanning X‐ray fluorescence and a geochemical end‐member mixing model, the record confirms dust increased with human disturbance beginning around 1880 CE, reversing a long‐term decreasing trend potentially related to changes in effective moisture, wind, and vegetation. However, increases in dust mass accumulation rates do not correspond to years or periods of drought, as characterized by tree rings. This result suggests sediment supply and transport mechanisms have a strong influence on dust deposition. The record shows the Southwest is naturally prone to dustiness; however, human disturbances have a large influence on dust emissions, which can be mitigated by changing land use. Plain Language Summary We use a sediment record to characterize the long‐term naturally driven changes in dust deposition over the past 4.5 millennia. The record shows a long‐term trend toward decreasing dust deposition, which was reversed with human‐induced land disturbance beginning in the middle nineteenth century. The long‐term trend may be related to effective moisture, wind, and vegetation. Nonetheless, there appears to be little relationship between known drought events and increased dust deposition, suggesting the controls on dust deposition include factors such as sediment source and transport mechanisms acting independently of drought. Key Points A new 4,500‐year‐long record of natural dust deposition shows a long‐term decreasing trend Drought variability, as characterized by tree rings, is not closely linked with dust mass accumulation Human disturbance substantially increased dust deposition since 1880 CE