Soil Dust: Big Impact of Tiny Specks
Eugene Shinn, V.H. Garrison, C.W. Holmes, D.W. Griffin, and C.A. Kellogg
U.S. Geological Survey, St. Petersburg, FL
We have hypothesized that the near demise of Caribbean coral reefs during the past three decades was hastened by pathogens and nutrients transported in African dust. If correct, the implications for interpreting ancient reefs and other ecosystems are significant. The geologic record indicates eolian dust has settled to Earth since the beginning of time. Research in the 1980s and 90s indicates soils and calcrete crusts throughout the Caribbean and Florida originated in the Sahel of Africa. Virtually identical paleosols and calcretes cap subsurface Pliocene and Pleistocene subaerial unconformities, proving a relatively long history of transatlantic transport. Commercial bauxite deposits in the Caribbean have also been attributed to aluminosilicate clays transported across the ocean.
Ice cores show that maximum dust generation and transport occur during glacial periods. However, the ongoing drought that began in North Africa around 1970 demonstrates significant transport also occurs during interglacials. About one billion tons of soil dust currently leave Africa each year and hundreds of millions of tons settle in the Caribbean, southeastern United States, as far west as New Mexico, and as far north as Maine. When Asian dust is added to the equation, annual global transport doubles to about 2 billion tons. Recent studies show that African dust crossing the Atlantic transports 1) living microbes, including various pathogens and viruses, 2) insects, 3) seeds, 4) feces, 5) phytoliths, 6) diatoms, 7) a variety of minerals and mineral nutrients, and 8) both short- and long-lived radioisotopes. Extrapolation of modern dust effects to interpret the geologic and paleontologic record requires caution because in addition to the natural components, soil dust today contains man-made chemicals such as pesticides, plasticizers, and dioxins.
AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming