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Dissolved aluminium (Al) is a primary tracer of atmospheric deposition to the open ocean. However, the impact of short-term environmental perturbations such as dust storms, sediment resuspension and rainfall events on the oceanic water column is poorly constrained due to the typically low temporal resolution sampling in open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a highly accessible deep oligotrophic water body featuring exceptionally high atmospheric deposition fluxes delivered by dust storms, which constitutes as the main terrigenous input to the GoA surface water. Here, we present a time series of dissolved Al and silicate (Si) concentration profiles sampled during 2017 and 2018, with a particular focus on daily time scale dust storms, episodes of sediment resuspension and rain events. We evaluate the results in conjunction with high temporal resolution measurements of airborne aerosols and sediment trap -based water column sinking particulate fluxes. Dissolved Al and Si concentrations ranged between 22 and 91 nmol kg−1 and 0.6 and 3.2 µmol kg−1, respectively. These two elements correlated at depth but decoupled in the upper water column. Counter intuitively, mixed layer Al (Al ML) inventories decrease with increasing aerosol loads, with dust storms promoting intense Al scavenging, causing scavenging rates to surpass dissolution rates and abruptly driving down Al ML by up to 14 %. Concurrently, post dust storm Al ML change rates increase linearly with increasing theoretical dissolution rates and thus net dissolution is predicted for higher dust loads than observed in this study. However, low seawater particle loads during low magnitude dust storms and deep mixing depths will result in conditions that favor scavenging. Similarly, a sediment resuspension event triggered a decrease of 34 % in the Al water column inventory. By contrast, wet deposition may enhance the soluble Al flux from mineral dust by a factor of 11. Atmospheric deposition flux estimates (29.8 ± 4.4 g m−2 year−1) calculated using long-term average Al ML and mixed layer depths agree with independent flux estimations. Conversely, fluxes calculated using discrete profiles yielded a wide range of values (8–93 g m−2 year−1). The combined results demonstrate that atmospheric deposition in the oceans acts as a long-term source for Al while concomitantly serving as a short-term sink through scavenging. The in-situ rates and insights presented here may be used to understand and quantify the true impact of abrupt environmental events on water column chemical compositions. [ABSTRACT FROM AUTHOR]

Lead (Pb) is a primary tracer of natural and anthropogenic processes in the marine environment, with atmospheric deposition being one of its main sources to open ocean surface waters. However, the impact of short-term (daily) dust storms on the oceanic water column is poorly constrained due to the typically low sampling temporal resolution in deep open ocean settings. The Gulf of Aqaba (GoA), northern Red Sea, is a deep oligotrophic water body surrounded by hyper-arid deserts with no major tributaries, and hence its surface waters receive limited terrigenous input, except from settling atmospheric dust particles. The GoA is highly accessible and therefore provides the opportunity to study the dynamics of seawater Pb chemistry across abrupt and short periods of enhanced atmospheric deposition. Here, we report a highly resolved time series of vertical profiles of dissolved Pb concentrations and isotopic compositions across daily-timescale dust storm events that occurred during 2018. GoA Pb concentrations range between 19 and 85 pmol kg−1, and the isotopic compositions of 206Pb/207Pb and 208Pb/206Pb are in the range of 1.163–1.190 and 2.062–2.093, respectively. These compositions reflect a mixture of multiple end members: seafloor sediments and open Red Sea waters, which modulate the long-term deep-water composition of GoA Pb, and settling aerosols, which shift the seawater composition towards anthropogenic values. The results show that dust storms impose strong perturbations of seawater compositions towards the anthropogenic aerosols end member, inducing increases of up to 54% in the Pb inventory in the upper water column. We propose a short-term dissolution-scavenging mechanism, whereby upon dust-seawater impact, the majority of the aerosol's soluble anthropogenic phases rapidly dissolve. The peak in the aerosol derived isotopic shift in the mixed layer is reached after 3–4 days. Simultaneously, Pb is re-adsorbed onto the sinking dust mineral particulates. Post dust storm Pb leaching and scavenging rates are modeled, yielding quantitative constraints on the connection between increasing dust loads and seawater Pb concentrations and isotopic compositions. Our findings demonstrate the short-term variable Pb response to dust storms and should be applied when interpreting open ocean surface water Pb patterns. • We present concentrations and isotopic compositions of Pb in the Gulf of Aqaba • Profiles of dissolved Pb were sampled at daily resolution across dust storms • A dissolution - scavenging mechanism quantifies the aerosol-seawater dynamics of Pb • The impact of aerosols on seawater Pb reaches its peak after 3–4 days • Pb scavenging rates are calculated and shown to increase with higher dust loads [ABSTRACT FROM AUTHOR]