In the deep basin of the Gulf of Eilat-Aqaba, there is a sediment layer approximately 5 kilometers thick, which mainly consists of clastic sediments originating from alluvial soil. These sediments rest above the bedrock, as described in the findings of geophysical and seismic mapping by Ben-Avraham (1985). The sediments on the seafloor of the gulf are primarily composed of quartz and feldspar (siliciclastic sediments of external terrestrial origin) and carbonate deposits – calcitic, containing varying concentrations of magnesium (high- and low-Mg calcite) – from internal marine sources, both planktonic and neritic, with grain sizes ranging from clay to sand (Friedman, 1985; Bialik et al., 2022).
Figure 1. A hyperpycnal undercurrent created by the influx of sediment-laden floodwaters into the northern Gulf of Eilat on January 27, 2013 (photo: Gil Koplovich). Taken from Katz et al. (2015).
The area surrounding the Gulf of Eilat is characterized by extremely arid conditions (less than 27 mm of rain per year) and consists of Precambrian bedrock with a cover of sedimentary rocks. In some areas, this cover includes sandy deposits at the lower part, with marine carbonate rocks above. In this region, there is no coastal plain, and the mountain slopes nearly reach the water's edge. During rainfall events, flash floods occur, carrying dust and sediment that have eroded from the rocks, and these serve as the primary mechanism for transporting sediments into the gulf. When floodwaters enter the northern Gulf of Eilat, they sink due to their high density beneath the sea surface and create a hyperpycnal undercurrent near/on the seafloor (Figure 1). Over time, the eroded particles (mainly clay and silt) will settle, adding several centimeters of sediment to the wide continental shelf (a slope approximately 2 km wide with an inclination of about 30 degrees) (Katz et al., 2015; Kalman et al., 2020). The ecosystem on this shelf is characterized by seagrass beds (Halophila stipulacea) where biological activity, sediment mixing, and sediment resuspension occur due to fish, meiofauna, and benthic organisms (Oron et al., 2014). To the south of the shelf, around the coral reefs, sediments with coarse grain sizes, originating from coral fragments, calcareous algae, and skeletal remains of benthic organisms such as foraminifera, mollusks, and echinoderms, can be observed (Friedman, 1985; Katz et al., 2015).
Dust originating from storms (mainly from the Sahara Desert) also serves as a source of terrestrial particulate matter that settles into the waters of the Gulf of Eilat. Dust deposits in the gulf are measured at approximately 20-30 µg m^-3, reaching maximum values of about 700 µg m^-3 during exceptional dust storms, with annual particle deposition rates of around 34.7 g m^-2 year^-1 (Blonder et al., 2017; Torfstein et al., 2020).
Another source of sediments in the Gulf of Eilat comes from carbonate particle deposits (biogenic and inorganic CaCO3), with an estimated input ofabout 7.3 ± 0.4·10^10 kg year^-1. Of these, 80 ± 5% originate from calcareous planktonic skeletons, and 20 ± 5% come from coral reefs (Steiner et al., 2014). Consequently, the carbonate mineral content in the seafloor sediments constitutes up to 38% (by weight of total sediments), thanks to the skeletal plates from coccolithophorids (planktonic single-celled organisms) (Katz et al., 2015; Steiner et al., 2019).
The sedimentation rates on the seafloor of the Gulf of Eilat range from a maximum value of 0.105 ± 0.020 to 0.35 ± 0.23 cm per year, while the sediment mixing rate reaches a maximum of about 2.18 ± 0.69 cm^2 per year (Pittauerov et al., 2014; Al-Saqarat et al., 2017). The underwater dynamics of particle and sediment cycles are complex due to the small size of the Gulf of Eilat. From the moment the sediments reach the margins of the gulf and surface waters, there is a delay (lag) before they finally reach the deep-sea floor, due to processes such as resuspension and redistribution, transport, and focusing of sediments. These processes occur due to weathering, storms, and even seasonally during the vertical mixing of the water column, depending on the depth and intensity of the mixing (Ash-Mor et al., 2017; Torfstein et al., 2020).
Figure 1. A hyperpycnal flow - turbidity current that originated from discharge of sediment-laden flood waters into the northern Gulf of Aqaba-Eilat on January 27th, 2013. (Photograph by Gil Koplovitz). Adapted from Katz et al. (2015).
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