The contemporary physical and chemical flux of aeolian dust: A synthesis of direct measurements of dust deposition

The deposition Of aeolian, or windblown, dust is widely recognized as an important physical and chemical flux to ecosystems. Dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients. There have been many studies that characterize the physical and chemical composition of dust. However, few studies have synthesized these observations in order to examine patterns geochemical fluxes. We have compiled observations of dust deposition rates, particle size distributions (PSD), mineralogy and bulk elemental and organic chemistry. The rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m(-2) yr(-1). Sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions. When compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales. The distance from the source region that dust is deposited also influences the particle size distributions, mineralogy, and chemical composition of dust; however, more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns. On average, the concentrations of most major elements (Si, Al, Fe, Mg, Ca, K) in aeolian dust tend to be similar (+/- 20%) to the composition of the upper continental crust (UCC), but there is substantial variability from sample to sample. In contrast, some elements tend to be depleted (Na) or enriched (Ti) in dust, likely as a result of soil weathering processes prior to dust emissions. Trace elements, especially heavy metals, are consistently enriched in dust relative to the UCC. Ecologically important nutrients, such as N and P, are also present in dust deposition. The geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions. We calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition. These estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models. (C) 2009 Elsevier B.V. All rights reserved.