Desert flash floods form hyperpycnal flows in the coral-rich Gulf of Aqaba, Red Sea

- Flashfloods cause hyperpycnal flows in the hyperarid Gulf of Aqaba (GOA).
- First direct observations and video recording of a hyperpycnal flow underwater.
- Sediments discharge from ephemeral rivers far exceed airborne fluxes to the GOA.
- Flood sediments deposited on the shelf are later transported to the deep basin.
- Intermittent flashfloods preclude coral growth at the northern shelf of the GOA.

Running rivers are very scarce in globally distributed hyperarid and arid coastlines (∼28,000 km worldwide), and it is ephemeral rivers that carry most terrestrial sediment into the sea in these regions. However, there is very little information regarding the contribution of terrestrial sediment and dynamics of transport of sediment that enter marine basins from these rivers. One hyperarid region, the Gulf of Aqaba received an exceptional number of flashflood events during the winter of 2012-2013. The results illustrate, for the first time, how the high volume of flashflood sediment influences the distribution of coral reefs; dwarfs the contribution of airborne dust; elevates floodwater densities to produce hyperpycnal flows, despite highest ocean salinities; and is subsequently transported to the deep basin where it may be preserved as a climate archive.