Origin of submarine channel north of Hanish Sill, Red Sea

Submarine channels several kilometres wide can be found near sills between major basins but they typically lie on the sides of the sills where dense bottom waters passing between the basins form gravity currents. In the southernmost Red Sea, in contrast, an 8 km-wide and 100- to 250-m deep channel lies on the north side of Hanish Sill, in an area where the strongest bottom currents flow southward, associated with winter expulsion of dense saline Red Sea deep water. Current meter data collected 10 m or more above the seabed over the sill reveal speeds occasionally exceeding 1 m s-1, which are sufficient to mobilize very coarse sand and have likely prevented deposition of finer sediments in the channel, particularly for parts of the channel affected by Red Sea Outflow Water (RSOW). However, the channel extends below 200 m depths, where Red Sea Deep Water is more sluggish (typically &lt; 1 cm s-1). Although the stronger currents may help to maintain the upper channel morphology, it is unclear how they would have created the channel, nor can modern currents explain the deeper parts of the channel. The channel is straight and runs parallel with the spreading rift to the north, suggesting that faults may underlie the channel, though a tectonic origin (graben) is not supported by Bouguer gravity anomalies, which reveal no underlying structure. Alternatively, the channel may have originated much earlier, from massive inflow of Indian Ocean water into the Red Sea following earlier isolation and drawdown of its level. These and other possible origins of the channel are discussed in the light of limited public data from the area.</p