TRANSPORT OF DESERT DUST TO THE RED SEA DURING LATE QUATERNARY (LAST 150 KA): EVIDENCE FROM DEEP SEA CORES

The Red Sea (RS), situated between the Sahara and Arabia deserts, is an ideal archive for reconstructing dust transport and atmospheric circulation in this region during the late Quaternary. The RS seawater composition was strongly affected by glacial-interglacial sea level changes due to its location and its tectonic settings (e.g. Semi-enclosed basin). Thus, the d¹⁸O ratio was found to be greater than that in open oceans. This allowed for high–resolution chronostratigraphy. The isotopic and chemical composition of the dust that accumulated on the sea floor was analyzed. Results show that the dust, settled on the sea floor, originated from different sources.

This work focuses on provenance characterization of fine detritus <63µm (interpreted as desert dust) that was deposited in the northern RS and sampled in deep-sea core KL-23 (25°44,88N 35°03,28E). Two time intervals that cover the penultimate and last glacial/interglacial transitions (between 150-110 kyr BP and 20-2 kyr BP respectively) were examined. The desert dust grain size distribution was studied in the bulk sediment of the acetic acid insoluble residue. Additionally the carbonate-free <63µm sediment fraction was used for analyzing the mineralogical composition chemical composition, and ¹⁷⁶Hf/¹⁷⁷Hf, ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotope ratios. The isotopic ratios suggest that the desert dust in this region is derived from two main sources, a “granitic” source with eNd < -8 and 87Sr/86Sr > 0.711 and another source with more “basaltic” composition (e.g. eNd > -4 and 87Sr/86Sr < 0.709). The “granitic" source was more dominant during glacials, while the “more basaltic” dust was dominant during interglacials.

The closest possible sources for the “more basaltic” dust are the Neogene-Quaternary basaltic fields located on the north-eastern side of the RS. This suggests firstly that the extremely arid area of the RS had significantly wetter periods, allowing basalts erosion. Secondly this may suggest the predominance of easterlies during interglacials. Sharp excursions in the eNd, ⁸⁷Sr/⁸⁶Sr and ¹⁷⁶Hf/¹⁷⁷Hf values occurred across the MIS 6/5 and MIS 2/1 transitions. This is likely a reflection of the erosion and accumulation of "more basaltic” dust and its wash to the RS during sapropel-equivalent episodes.