Regional Differences In Seasonal Dust Deposition Rates In the Southwestern U.S

Dust generation in the southwestern U.S. is a complex response to the interaction of weather cycles (ENSO), changes in annual and perennial plant cover, and hydrology of dust-source areas. Annual vertical dust-deposition rates, a proxy for dust generation, have been measured in the Mojave and southern Great Basin deserts (M-SGB) since 1984, and seasonal rates (winter-spring and summer-fall) in the M-SGB and eastern Colorado Plateau (CP) since 1999. Previously published data show that peaks in annual dust flux correspond with both La Nina (dry) conditions and strong El Nino (wet) periods, mediated by factors such as the hydrologic condition of surface sediments and vegetation growth and mortality.

New seasonal data for the M-SGB desert and the eastern CP demonstrate that the deposition rates of eolian fines (silt + clay) and CaCO₃ on the CP in most seasons and years are at least twice as large as those in the M-SGB region. Silt-clay and CaCO₃ fluxes in the CP area are also strongly seasonal, being about twice as high in the summer-fall than in winter-spring. Seasonal differences in silt-clay and CaCO₃ flux are smaller in the M-SGB region, and in some years are actually higher in the winter and spring. Soluble salt fluxes are usually higher in the winter-spring period in the M-SGB region, but the reverse is true in the eastern CP. These regional differences are likely the result of seasonal rainfall patterns, because the eastern CP has highest precipitation during summer monsoon storms that generate strong convective winds; in contrast, the M-SGB region has highest precipitation in the winter, with the easternmost M-SGB sites having a secondary precipitation peak in the summer. Higher soluble-salt flux in the M-SGB is generated from playas with shallow groundwater and is a response to winter-wet conditions, especially in strong El Nino years.