The Strait of Tiran (~ 4.5 km, 2.8 mi, wide), linking the Red Sea and the Gulf of Aqaba, is characterized by 4 small, shallow carbonate platforms separated from the Sinai coast by the deep (^approx 280-m, 920-ft) Enterprise passage and from the Saudi Arabia coast by the shallow (^approx 75-m, 250-ft) Grafton passage.

Intense evaporation (3.5-5.0 m/yr, 11.5-16.5 ft/yr) in the interior basin of the Gulf of Aqaba suggests the presence in the strait of an inverse stratified flow, similar to the Strait of Gibraltar. As no direct observations of currents existed, 12 current meters were deployed for 5 weeks across the 2 deep passages in winter 1982. Other physical data included salinity-temperature-depth (STD) transects and wind and tide measurements.

The deeper Enterprise passage shows a remarkably steady, strongly developed 2-layered flow structure, with upper layer net inflows of 30-40 cm/sec (12-16 in./sec) and lower layer net outflows of 55-60 cm/sec (22-24 in./sec); the shallow Grafton passage is completely in the upper layer, with net flows of 30-40 cm/sec (12-16 in./sec) directed northerly into the Gulf against the wind.

High-resolution seismic profiles, side-scan sonar data, echo-sounder profiles, and direct observations of the bottom indicate morphological responses in sill geometry and sedimentation patterns that reflect controlling dynamics. For example, morphological features associated with the shallow sill channels are controlled by the upper-layer gulfward flow. Current and salinity data in the deep passage suggest outflow-oriented features that are as yet unconfirmed by seismic profiles. Bottom samples suggest that sill accretion is accomplished primarily by the buildup of coralline algae, as well as stabilization of coarse bottom sediments by both organic and inorganic cements. Another striking feature is the occurrence of large and numerous patch reefs on the windward (northern) slope of th shallow platform margins. Storm wave forces on the platform front apparently dislodge carbonate blocks that function as substrates for thriving patch reefs. These processes are likely characteristics of entrances to tectonic troughs in early stages of ocean-basin formation.

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