Relative water transparency and color in the northern part of the Tropical Atlantic

Abstract

By now a large data array, which made it possible to construct maps of the depth distribution of Secchi disk visibility in the World Ocean, has been accumulated. However, the updating of this database remains urgent, since there is not enough data for constructing reliable maps in some areas of the ocean. This is also related to the tropical area of the Atlantic Ocean, in particular. In the present article the statistically reliable maps of depth distribution of Secchi disk visibility Z_white (relative transparency) and water color distribution N_color in the northern part of the tropical area (0-12 °N) of the Atlantic Ocean in summer and winter are constructed based on the multiannual observational data obtained in 1984-1990. It is shown that the basic features of the fields Z_white and N_color are explained by waters dynamics in the indicated region that results in formation of the upwelling and downwelling zones where water transparency decreases and increases, respectively. Here, the large-scale currents form two following gyres having different direction: the tropical cyclonic gyre, where an upwelling takes place (divergence zone) and the tropical anticyclonic one, where a downwelling occurs (convergence zone). Also, near the equator, due to a change in the Coriolis force sign, there is a divergence of the South Passat Current, accompanied by the upwelling. The areas where Z_white > 41 m were revealed. It is shown that in these areas the anticyclonic vorticity of currents with downwelling was observed. As for the seasonal variability, it was established that In winter water transparency is higher and its color is more intensive than in summer; it is explained by the seasonal variability of currentsand the related water vertical motions.

Keywords

tropical area of the Atlantic Ocean, Secchi disk, transparency and color of water, divergence, convergence.

DOI: 10.22449/1573-160X-2017-4-59-65

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