Water Masses and Circulation in the Chain Fracture Zone (Equatorial Atlantic)

In this study, we discuss the water masses and their transport in the Chain fracture zone (CFZ), which is a poorly studied part of the Equatorial Atlantic. Our study is based on measurements carried out during the 63rd cruise of R/V “Akademik Ioffe” in 2022. We identified water masses in the CFZ, determined their physical and chemical properties, localized their boundaries and components of the North Atlantic Deep Water (NADW), and calculated the transport of water masses. A four-layer structure of the NADW was identified with two components of middle NADW, which are defined by minimal and maximal oxygen concentrations. The upper boundary of the Antarctic Bottom Water (AABW) corresponds approximately to the isotherm θ = 1.5 °C. The assessed proportion of AABW in the bottom layer at the western entrance to the CFZ is 50%, and not higher than 33% at the eastern exit from the CFZ. For the first time, instrumental observations were carried out at the exit of the CFZ and in its western part. They showed that the AABW flux has an intensity of about 0.02–0.5 Sv depending on the upper boundary of AABW and moves through a passage in the northern wall (at 13° W), and not through the main sill.