Physical Oceanography (Feb 2017)
Spectral Characteristics of the Beam Attenuation Coefficient in the Atlantic Ocean Tropical Area
Abstract
The results of measurements of the ε(λ) beam attenuation coefficient (BAC) spectral distribution in the surface waters of the North Atlantic tropical region (NATR) are represented. The data were obtained in the 27th cruise of R/V Akademik Vernadsky (January–April, 1984). According to the data of the beam attenuation coefficient spectra measurements in the surface waters of the tropical Atlantic northern part, the characteristics of the spectra (440–675 nm range) were obtained. Also, the change of the spectra shape the in the NATR waters with the attenuation coefficient increase was considered. Spectral distributions of the attenuation coefficient in the waters of the principal large-scale NATR currents and in the coastal African waters are presented. A comparison of the mean spectra in oligotrophic waters of the tropical Atlantic and the Pacific Ocean was carried out. It showed the same pattern of the spectral distribution of the attenuation coefficient in these regions. For an array of empirical functions ε(λ) in the NATR waters, the expansion into orthogonal eigenvectors was carried out. The possibility to reconstruct the spectra using the first orthogonal vector, i.e. by measuring the attenuation coefficient at one wavelength, is shown. The optimal wavelength values, which should be used to reconstruct the spectra, are indicated. The relation of the chlorophyll concentration in the surface ocean waters of the NATR with the beam attenuation coefficients in three sections of the spectrum with wavelengths of 440, 500 and 551 nm was established. In the NATR coastal waters the relation Cchl = f[ε(λ)] should be considered separately, since it differs significantly from the one in ocean waters. The chlorophyll and attenuation coefficient relations in NATR ocean waters established in this work should be characterized as regional.
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