The sinking flux of marine particles forms the sedimentary record that documents the history of the oceans and the atmosphere, which reflects the particle source (e.g. dust deposition, fluvial input, biogenic) and the processes altering their composition, such as weathering, scavenging or reverse-scavenging, and formation of authigenic phases. Decoupling between the source composition, weathering history and marine biogeochemical processes is important for both studies of modern biogeochemical cycles in the oceans and their history on geological timescales.
In this study, we examine the changes in the chemical and uranium isotopic composition (234U/238U) of atmospheric dust collected between 2009-2019 and sinking particle collected between 2015-2018 in the Gulf of Aqaba, northern Red Sea. The samples were sequentially leached to extract four mineralogic fractions from each sample.
Changes in chemical and isotopic composition allow to deconvolve the end member components, showing that shallow samples are enriched in lithogenic elements (e.g. Fe, Ti, Li), similar to dust, while deep samples are enriched with Th and Ba, presumabely scavenged from the water column. The carbonate phase is relatively enriched with Ca, Mn, and Zn, reflecting biogenic sources.
Systematic seasonal and vertical shifts are identified based on the chemical composition and flux of sinking particles, combined with depleted (234U/238U) in deep (0.75-0.85) compared to shallow (0.91-0.93) waters. Moreover, the (234U/238U) of the silicate fraction yields comminution ages of 20-100 ka for dust, 20-200 ka for most marine particles, with values >500 ka for the deep-water end member.
The coupled time series of sequentially leached dust and sinking marine particles yields a unique understanding of the dynamics of the source to sink process. Combined with comminution ages, this provides a quantitative description of the transportation of particulate matter across the Sahara-Arabia Desert belt and their geochemical transformation while sinking through the oceanic water column.