Abstract
African dust has long been hypothesized to supply new sources of iron and phosphorus (Fe and P) that can stimulate primary productivity in both the nitrogen-limited Tropical Atlantic Ocean and the P-limited Amazon rainforest leading to the sequestration of atmospheric carbon dioxide. However, several major gaps in understanding exist that call into question the validity of this hypothesis, including how soluble and therefore biologically available are nutrients in African dust?; how does the source region and extent of chemical aging of African dust impact its biogeochemical effect?; and is dust the only atmospheric source of nutrients that elicits an appreciable impact on terrestrial and marine biogeochemical cycles? Recent major volcanic eruptions and wildfire events have generated special interest in the last question as these aerosol types are thought to provide more bioavailable nutrients, particularly to the open ocean. In this talk, we synthesize traditional bulk chemical and single-particle techniques with isotopic fingerprinting and incubation experiments to holistically compare the nutrient content, solubility, and bioavailability of different sources of African dust, biomass burning, and volcanic ash. Several major findings will be presented including how variability in the source of African dust transported to the Amazon leads to differing biogeochemical outcomes, the important and underappreciated role of African smoke as a major and sometimes dominant source of soluble P transported to the N Atlantic and Amazon Basin, the variable chemical composition of volcanic ash, as well as the impact of volcanic ash on P and Fe delivery and cycling to the ocean. Overall, our results suggest that several long-standing hypotheses regarding the dominant impact of African dust transport on nutrient delivery to the Amazon and Tropical Atlantic Ocean need to be revised to account for the important roles of wildfire smoke and volcanic ash on marine and terrestrial biogeochemical cycles and climate.