EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Water Masses Chemical Properties in the Western Tropical Atlantic Ocean

Renan Luis Evangelista Vieira1,2, Leticia Cotrim da Cunha1,2, Ricardo de Almeida Keim1,2, Carlos Augusto Musetti de Assis1,2, Jessica da Silva Nogueira1,2, Raquel Avelina da Conceição dos Santos1,2, Thiago Veloso Franklin1,2, Rafael Avelino da Conceição dos Santos1, and Paula Charnaux Macedo1
Renan Luis Evangelista Vieira et al.
  • 1University of State of Rio de Janeiro, Rio de Janeiro, 20550-900, Brazil
  • 2Brazilian Ocean Acidification Network – BrOA, Rio Grande, 96203-000, Brazil

Here we characterize the chemical properties of the water masses in the Western Tropical Atlantic Ocean according to their inorganic nutrient concentration: dissolved inorganic nitrogen (DIN), phosphate and silicate. We collected full-depth water samples from 16 oceanographic stations along the 38°W transect, from 1°S to 15°N during the PIRATA-BR XVIII cruise, in October-November 2018. In this region, the surface and subsurface circulation in the Atlantic Ocean displays complex seasonal patterns, under influence of the Intertropical Convergence Zone. The samples were collected from Niskin bottles closed in ten different depths, stored frozen, and later analysed through spectrophotometry. Besides that, the CTD-O2 data provided continuous salinity, temperature, and dissolved oxygen measurements, used to identify the water masses according to their thermohaline indexes. Six water masses were identified in the region based on their neutral density limits: Tropical Surface Water (TSW, γn < 24.448 kg m-3); South and North Atlantic Central Water (SACW and NACW, γn 24.448 – 26.815 kg m-3); Antarctic Intermediate Water (AAIW, γn 26.815 – 27.7153 kg m-3); North Atlantic Deep Water (NADW, γn 27.7153 – 28.135 kg m-3); and Antarctic Bottom Water (AABW, γn > 28.135 kg m-3).  The oligotrophic TSW is almost completely depleted in nutrients; Central Waters NACW and SACW have the following concentration ranges: DIN, 5 – 15 µmol/kg, phosphate, 0.5 – 1.0 µmol/kg, silicate, 5 – 20 µmol/kg); AAIW nutrient concentrations are DIN: 30 – 40 µmol/kg, phosphate: 1.5 – 2.5 µmol/kg, and silicate: 25 – 40 µmol/kg; NADW nutrient concentrations are DIN: 15 – 25 µmol/kg, phosphate: 1.0 – 1.5 µmol/kg) , and silicate: 20 – 45 µmol/kg; and AABW nutrient concentration ranges are: 40 – 80 µmol/kg silicate, 30 – 35 µmol/kg DIN, and 1.5 – 2.5 µmol/kg phosphate. North of 5°N up to 15°N, there is a region of lower oxygen and higher phosphate concentrations, comprising the central water and the upper AAIW layers, extending from 200 m to 800 m. This corresponds to the area under influence of the eastward flowing North Equatorial Counter Current (NECC) and North Equatorial Under Current (NEUC), which are both, in turn, influenced by the position of the Intertropical Convergence Zone (ITCZ). Further study directions include a detailed study of the multiple source waters to this central layer, associated to the regional circulation, and possible linking to the eastern tropical Atlantic oxygen minimum zone.

How to cite: Evangelista Vieira, R. L., Cotrim da Cunha, L., de Almeida Keim, R., Musetti de Assis, C. A., da Silva Nogueira, J., da Conceição dos Santos, R. A., Veloso Franklin, T., da Conceição dos Santos, R. A., and Charnaux Macedo, P.: Water Masses Chemical Properties in the Western Tropical Atlantic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9025,, 2021.