Hydrographic structure of brine-filled deeps in the Red Sea - new results from the Shaban, Kebrit, Atlantis II, and Discovery Deep

Hydrographic profiles with CTD and water samples from four brine-filled deeps in the Red Sea (Shaban, Kebrit. Atlantis II and Discovery Deep) were taken during the Meteor 31/2 expedition in February/March 1995. In the Shaban Deep area two smaller basins containing high saline brine were found in addition to the already known southern basins. Corresponding salinities (150.7 parts per thousand Cl in the upper brine section) and near equal brine levels (around 1325 m water depth) suggest subbottom connections below the sills separating the northern and southern basins. An insignificant decrease in temperature (to about 24.1 degrees C) has occurred in the upper brine since detection of the Shaban Deep in 1981 and no changes were found for the brine-seawater level. No significant changes have been observed in the Kebrit Deep over the last 23 years in temperature (24.3 degrees C), chlorinity (154.0 +/- 0.3 parts per thousand Cl), and brine level (1466 +/- 1 m). The transition from high saline brine to normal seawater salinity probably extends over a depth of only a few decimetres or less. Strong changes, however, were registered for the Atlantis II Deep. The temperature increase, known from numerous earlier investigations, continued. The gradient of increase was the steepest during the last 2.5 years and a temperature of 71.7 degrees C was reached in the lower brine of the SW basin. The structure of the lower transition zone, between about 1990 m water depth and high saline brine, has also changed significantly, now containing two convective layers with nearly constant temperatures (61 and 55 degrees C, respectively). The neighbouring Discovery Deep also shows evidence of increased hydrothermal activities. While the temperature was nearly constant (near 44.7 degrees C) until 1977, it has since increased to almost 50 degrees C and the brine level has risen by about 17 m. (C) 1998 Elsevier Science B.V.