Dust sources in Westernmost Asia have a different geochemical fingerprint to those in the Sahara

Abstract

Dust is an important component of Earth's climate system, directly affecting the global radiation budget and hydrological cycle. The interaction of aerosols with clouds and its impact on regional and global energy budgets remains one of the largest sources of uncertainty in climate model predictions. Records of terrigenous dust accumulation in geological archives also provide a potentially powerful way to assess past changes in hydroclimate. Western Asia, including the Arabian Peninsula, is second only to the Saharan Desert in contributing dust to the global atmosphere. Yet, while satellite-derived maps of dust source activation frequency (DSAF) provide an increasingly granular understanding of the different dust sources within these regions today, our ability to fingerprint their windblown contributions to geological archives is rudimentary, severely limiting the use of dust-based records to reconstruct past changes in continental hydroclimate. A main limitation is a poor understanding of the mineralogical and geochemical composition of the bedrock geology and, more importantly, of the readily deflated unconsolidated sediments in these regions. Here we use published data to produce a DSAF map, centred on the Arabian Peninsula and extending from North Africa to Western Asia (∼40-10 °N; ∼25–65 °E), and we present new radiogenic isotope (Sr and Nd) data from unconsolidated surface sediment samples at active dust-producing sites. We combine our new Sr and Nd data with sparse data on sediments from the literature and the DSAF data to define three new preferential dust source areas (PSAs) in Westernmost Asia: (i) the central belt of the Arabian Peninsula, (ii) the Southern Levant and (iii) Mesopotamia. All three of these PSAs are geochemically distinct from Saharan dust sources. Long-range sediment transport by the Blue Nile and its tributaries, and the Tigris-Euphrates river systems exerts a strong influence on the geochemical fingerprints of dust sources in the Eastern Sahara and Mesopotamia, respectively. The isotopic signature of active dust sources in the central belt of the Arabian Peninsula shows only modest correspondence to underlying bedrock geology suggesting wide scale mixing by aeolian transport internally and/or a weak imprint of palaeo humidity (e.g. localized river reactivation) on dust source composition in comparison to the Eastern Sahara. Our results provide surer foundations for fingerprinting the sources of continental dust accumulating in marine, lacustrine, speleothem and ice archives, an important step in improving our understanding of Quaternary rainfall climate in arguably the most water-stressed region on Earth.