Out of Africa and across Oceans: Geochemical Evidence for Long-Range-Transported Dust Additions to Soils on Insular Landscapes

The world's largest single source of dust at present is Africa, including both the Sahara and Sahel regions. Data from decades of dust-collecting studies and high-resolution satellite imagery demonstrate that dust from Africa is transported to the Mediterranean Sea, southern Europe and the Middle East, and across much of the Atlantic Ocean from the west coast of Africa to the east coasts of the Americas. We have studied the imprint of African dust additions to soils on nearby and distant islands. Islands often have bedrock of relatively uniform composition and have limited spatial extents of local sources as potential eolian inputs to soils. Geochemical studies show that African dust is transported long distances to islands and is added to soils, which can have a tremendous impact on insular ecosystems. Soils on islands in the Mediterranean (Mallorca), eastern Atlantic (Lanzarote and Fuerteventura in the Canaries), and western Atlantic (Florida Keys, Bahamas, Barbados, Jamaica, Bermuda) have mineralogical and geochemical evidence that demonstrates the importance of African dust inputs. However, the impact of African dust is variable: soils on the Florida Keys and Bahamas are derived dominantly from African dust, but soils on Jamaica and Barbados also have important inputs from volcanic ash. In addition to dust, soils on Bermuda and the Canary Islands are derived in part from local volcanic rocks that form the island substrates. Much attention has been paid to the effects of long-range-transported dust on planetary radiation balance, as a source of fertilizer for primary producers in the ocean, and as a possible carrier of pathogens. In addition, however, on islands where soil genesis would otherwise be limited, dust is often a crucial soil parent material and nutrient provider.