Variability in Sources and Concentrations of Saharan Dust Phosphorus over the Atlantic Ocean A. Gross,* ,† T. Goren, † C. Pio, ‡ J. Cardoso, ‡ O. Tirosh, † M. C. Todd, § D. Rosenfeld, † T. Weiner, † D. Custó dio, ‡ and A. Angert † † The Institute of Earth Sciences, The Hebrew University of Jerusalem, Israel ‡ Centre for Environmental and Marine Studies, Department of Environment, University of Aveiro, Portugal § Department of Geography, University of Sussex, Brighton, U.K. *S Supporting Information ABSTRACT: Saharan dust that is transported over the Atlantic Ocean provides an important input of phosphorus (P) to the oligotrophic waters of ocean and the P-depleted rain forests of America. To establish more firmly the role of Saharan dust events as P suppliers, the dust P sources needs to be identified. From analysis of phosphate oxygen isotopes of all the major Saharan dust events of 2011 over the Cape Verde islands in the northeastern Atlantic, supported by remote-sensing imagery, we infer that the dust P originates from widespread sedimentary sources and magmatic P “hot spots”, in which the latter enrich the dust in bioavailable P. The fraction contributed from each source varied markedly between dust events. We also found that phosphate from the Bodé lé depression is not evident in Cape Verde. Our results provide new information for global biogeochemical studies and suggest that identification of Saharan dust P sources is required to improve their accuracy. ■ INTRODUCTION Millions of tons of dust particles are eroded every year from the Sahara desert soils and are blown over the Atlantic Ocean and as far as the Amazon basin. 1 This dust flux acts as an important supplier of P to the Atlantic Ocean 2,3 and America’s tropical forests. 4,5 The sources and transport pathways of Saharan dust involved in such long-range transport vary greatly in time and space in response to the marked seasonal variations in the metrological conditions over the Sahara desert. 6,7 As a result, different Saharan dust events may carry variable amounts of P because the dust P concentrations may depend on the P content of its source. 8 Hence, accurate estimation of the impacts of Saharan dust P on the productivity of these ecosystems can be enhanced by reliable data on the dust P sources, which are currently poorly characterized. Remote sensing techniques have proved useful for quantifying the levels of dust in the atmosphere and revealing its transport pathways and its active sources. 9 −12 However, the sources, concentrations, and biological availability of the deposited P, as well as other geochemical characteristics of the dust, can be truly determined only by direct geochemical examination of the transported particles. This is challenging for two reasons. First, an adequate technique for identifying the terrestrial sources of atmospheric P has been developed only recently. 13 Second, collecting Saharan dust samples over the Atlantic Ocean is not trivial, and the recent major measurement campaigns conducted on dust emitted from the western Sahara (e.g., SAMUM-1 and SAMUM-2) did not involve P analysis. 14 In this study, we present P measurements from all the major Saharan dust events of an entire year over the northeastern Atlantic. We examined dust samples collected on Santiago Island of the Cape Verde archipelago [14.926°N, 23.495°W (Figure 1)] during all major dust events over the period from January 2011 to January 2012 inclusive, as part of the CV-Dust campaign. 15 This archipelago is located in the northeastern Atlantic Ocean (Figure 1), in the proximity of the Sahara (∼650 km off the coast of western Africa) and within the dominant dust transport pathway from Africa across the Atlantic toward the Americas. 7,16 Our observations can be understood in the context of the annual northward migration of the Saharan dust plume from winter to summer, 9 which produces two strong dust seasons. 16 The winter southern route extends over the Atlantic along ∼5°N toward equatorial South America. The summer northern route centered at ∼18°N extends toward the Caribbean. In winter, dust remains close to the surface, and as a result, episodic dust events are detected at Cape Verde 17,18 (section 1 of the Supporting Information). Therefore, the location of the islands is excellent for monitoring Saharan winter dust events and measuring P that is deposited in the eastern Atlantic and subsequently at the Amazon basin. Received: December 14, 2014 Revised: January 15, 2015 Accepted: January 20, 2015 Published: January 20, 2015 Letter pubs.acs.org/journal/estlcu © 2015 American Chemical Society 31 DOI: 10.1021/ez500399z Environ. Sci. Technol. Lett. 2015, 2, 31−37