The impact of a freshwater diluted plume on spatial halite accumulation in a hypersaline lake: Direct observations from the Dead Sea

The role of freshwater inputs and salinity gradients in hypersaline basins is crucial for understanding the formation of evaporitic sequences. However, this role remains poorly understood, as it involves complex processes such as mixing across density gradients, plume dynamics and air–water interactions. This study addresses this gap by investigating how a diluted buoyant plume, formed by freshwater inflows, affects spatial halite accumulation in the Dead Sea, a modern analogue for ancient evaporitic environments. In situ measurements of halite accumulation rates were conducted along transects extending from nearshore freshwater inflows (discharging ~70 × 10⁶ m³year⁻¹), through the diluted plume, and into regions beyond the dilution effect. These measurements were complemented by analyses of spatiotemporal limnological conditions (salinity, temperature, turbidity and halite saturation), which are influenced by wind-wave action. The diluted plume exhibits a distinct salinity structure, with full dilution at the freshwater spring discharge and exponential decay in both horizontal and vertical directions: horizontally, it decays over ~500 m, with surface dilution extending ~2 km offshore, and vertically it decays over ~0.06 m, creating a thin, highly diluted upper layer of about 1 m thick. Consequently, halite accumulation rates increase along the transect from the freshwater inflows towards deeper areas as the dilution effect diminishes. This process is controlled by (i) the transport of supersaturated brine and halite crystals from the non-diluted environment under the diluted plume and (ii) direct precipitation of halite when the diluted plume undergoes mechanical mixing. Persistent undersaturation in the upper diluted plume layer prevents halite precipitation and, when combined with the declining lake level, leads to the dissolution of previously deposited halite layers in deeper areas. The absence of halite near the freshwater inflow and the thickening of halite towards the depocenter are observed in early Holocene Dead Sea basin halite sequences and other global halite records.