Vertical, horizontal, and temporal changes in temperature in the Atlantis II and Discovery hot brine pools, Red Sea

In October 2008, we measured temperature and salinity in hot, hypersaline brine filling the Atlantis II and Discovery Deeps on the Red Sea spreading center west of Jeddah, Saudi Arabia. In agreement with previous observations in the Atlantis II Deep, we found a stack of four convective layers with vertically uniform temperature profiles separated by thin interfaces with high vertical temperature gradients. Temperature in the thick lower convective layer in the Atlantis II Deep continued to slowly increase at 0.1 °C/year since the last observations in 1997. Previously published data show that the temperature of all four convective layers increased since the 1960s at the same rate, from which we infer that diffusive vertical heat flux between convective layers is rapid on time scales of 3–5 years and, thus, heat is lost from the brine pools to overlying Red Sea Deep Water. Heat budgets suggest that the heat flux from hydrothermal venting has decreased from 0.54 GW to 0.18 GW since 1966. A tow-yo survey found that temperature in the upper convective layers changes about 0.2 °C over 5–6 km but the temperature in the lower brine layer remains constant. Temperature in the lower convective layer in the Discovery Deep remains unchanged at 48 °C. To explain these results, we hypothesize that heat flux from a hydrothermal vent in the floor of the Discovery Deep has been stable for 40 years, whereas temperature of the brine in the Atlantis II Deep is adjusting to the change in hydrothermal heat flux from the vent in the Southwest Basin. We found no changes in the upper transition layer at 1900–1990 m depth that appeared between 1976 and 1992 and suggest that this layer originated from the seafloor elsewhere in the rift.