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The yellow substance (YS) content in the surface waters of the eastern part of the Atlantic Ocean tropical zone is studied. The investigations are carrie out on the polygon with coordinates 3 °S – 11 °N; and 19° – 22 °W. To define the YS content in the polygon waters, a new method is developed. Usually the YS content in water is assessed based on the value of its light absorption coefficient on the wavelength 390 nm. It is defined, first, by measuring the seawater absorption coefficient. Second, for the surface waters, the phytoplankton pigments’ absorption coefficient is subtracted from the seawater absorption coefficient; and for the deep-sea waters, the abundant, as compared to the seawater, absorption is attributed to yellow substance [1]. To define the YS content, the paper represents the method for measuring the beam attenuation coeffiient in the filtered seawater. In the suspension-free water the value of the beam attenuation coeffiient depends on light absorption by yellow substance and light attenuation by water the value of which for water is known. Thus, it is possible to define the YS absorption coefficient. For this purpose, to purify seawater of admixture, the filters with a pore diameter not exceeding 0.04 mcm are to be used. The particles whose diameter is smaller than 0.04 mcm produce no influence upon the water optical characteristics. The investigation implies that the seawater is purufied by the filter the pore diameter of which is 0.4 mcm. In order to take into account the light attenuation coefficient of the particles that remained in the filtrare and the diameter of which is smaller than 0.4 mcm, a special method is developed. The spectral variability index of the YS light absoprtion coefficient is μ=0.0124 nm in the waters of the region under investigation that is characteristic of mesotrophic waters. Application of the data from [6] on relation of the absorption coefficient of YS with its concentration permits to calculate the YS concentration in the polygon surface water. In the eastern part of the polygon the YS concentration exceeds the one in the western part that is explained by the fact that the currents from the upwelling zone on the Guinean shelf edge bring the waters with high YS concentration to the polygon. The YS contribution to the attenuation coefficient in the oceanic waters of different type being compared to the model simulations in [1], shows that, in general, the polygon waters are mainly similar to the coastal waters on the depths smaller than 100 m.

Yellow substance in the surface waters of the eastern part of the Tropical Atlantic