Microspectroscopy reveals dust-derived apatite grains in acidic, highly-weathered Hawaiian soils
Christian Vogel, Julian Helfenstein, Michael S. Massey, Ryo Sekine, Ruben Kretzschmar, Beiping Luo, Thomas Peter, Oliver A. Chadwick, Federica Tamburini, Camille Rivard, Hannes Herzel, Christian Adam, A. Real, Hiram Castillo‐Michel, Lucia Zuin, Dongniu Wang, Roberto Félix, Benedikt Lassalle‐Kaiser, Emmanuel Frossard
Abstract
Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradient were analyzed with bulk (X-ray diffraction and P K-edge X-ray absorption near edge structure) and microscale (X-ray fluorescence, P K-edge X-ray absorption near edge structure, and Raman) analysis methods. In the wettest soils, apatite grains ranging from 5 to 30 µm in size were co-located at the micro-scale with quartz, a known continental dust indicator suggesting recent atmospheric deposition. In addition to co-location with quartz, further evidence of dust-derived P included backward trajectory modeling indicating that dust particles could be brought to Hawaii from the major global dust-loading areas in central Asia and northern Africa. Although it is not certain whether the individual observed apatite grains were derived from long-distance transport of dust, or from local dust sources such as volcanic ash or windblown fertilizer, these observations offer direct evidence that P-containing minerals have reached surface layers of highly-weathered grassland soils through atmospheric deposition.