Water Masses of the Guiana Basin

We present the results of our expeditionary studies of the water structure on a section across the Guiana basin in the western part of the Atlantic Ocean in January 2022. The section corresponds to almost the shortest distance between South America’s continental slope and the Mid-Atlantic Ridge. We identified various water masses corresponding to the study area, determined their physical and chemical properties, and located their boundaries regarding the position of their properties’ maximal vertical gradients. Particular attention was paid to the components of North Atlantic Deep Water (NADW). On the section, we identified four NADW components: upper NADW with salinity maximum and minimum in silicate, two middle NADWs determined by different extremes in dissolved oxygen, and lower NADW with maximum oxygen and minimum phosphate. The lower boundary of NADW corresponds approximately to the isotherm θ = 1.6–1.8 °C. The proportion of Antarctic Bottom Water (AABW) was calculated for the bottom layer; its maximal amount was about 40% on the section.