Discovery of a large brine deep in the northern Red Sea

The Red Sea is formed of marginal areas, shallower than 1,000 m, which are separated by a deeper axial zone. The axial zone can be subdivided into three main segments. The southern segment is a relatively simple trough which, north of 16° N, corresponds to an oceanic rift¹. The middle segment, from 19°30' n to 23°50' N, is characterized by the presence of about 15 closed depressions or axial deeps, ranging from several kilometres to less than a kilometre in length, and containing hot of cold brines underlain by their associated deposits of soft- and fine-grained metalliferous muds^1-3 The northern segment of the axial zone is shallower, with depths rarely exceeding 1,500 m, and has a smoother relief than the southern and central segments. In the northern segments, south of the Al Wajh depression at 25°25' N, the axis strikes north-south (Fig. 1). North of the depression, towards the approaches of the Gulf of Suez, the strike is NNW-SSE. The small, circular (1 km diameter) Oceanographer deep is located⁴ along the western border of the axial zone of this northernmost segment. The Jean Charcot deep, which we discovered on 3 December 1983 during a cruise of the RV Jean Charcot, lies near 25° 15' N, 35°22' E, close to the axis of maximum depth of the same segment. In contrast with the magnetically quiet neighbourhood, a strong dipolar magnetic anomaly typifies this deep, which in spite of intensive international surveys, is the first brine deep to have been discovered in the Red Sea in the past 10 years.