Statistical analysis of horizontal distributions of optical characteristics and temperature in the North Atlantic

Continuous shipboard measurements of optical properties and temperature (T) carried out in north part of the Atlantic ocean in summer 1988 during research vessel "Academic Kurchatov" cruise in waters with different productivity were analyzed. Measurements were carried out in the subsurface layer (at depth of 6 m) at 20 transects about 100 km long. The set of optical properties including green-blue ratio G=L(550)/L(440) and sea water fluorescence F expressed variability of chlorophyll concentration. These observations were accompanied by measurements of vertical profiles of the beam attenuation coefficient and chlorophyll concentration performed at stations restricting the transects. Regression and spectral analysis were used to investigate spatial series of hydrooptical characteristics. High correlation between green-blue ratio and surface values of the beam attenuation coefficient (the correlation coefficient r=0.99), and between green-blue ratio and chlorophyll concentration (r=0.95) were found. The logarithmic regression between mean values of green-blue ratio and its standard deviations with correlation coefficient r=0, 95 was obtained; the correlation between standard deviation and the average value of temperature was negligible. Dependence of mean values G~ on mean values T~ at the study area was immerse. Spectral analysis of spatial distributions included computation of power spectra, coherence and phase shift between green-blue ratio and temperature variations. It was shown that values and slopes of power spectra of G increased with water productivity. Power spectra were approximated by power law with slopes from -1, 4 to -2, 6 for G-spectra and from -2, 4 to -3, 5 for T-spectra. Coherence spectra between G and T fell with decreasing of length scales, values of coherence spectra at scales about several kilometers were negligible in low productivity waters and increased with chlorophyll concentration. Phase shift between green-blue ratio and temperature variations was usually close to 180/spl deg/. The alternative statistical methods were developed for study of distributions of number G and T heterogeneities in dependence of their sizes and amplitudes. These distributions were shown to be described by exponential functions. Steepness of G distribution was found to depend on water productivity. The results of statistical analysis for the North Atlantic were confirmed by analogous results for data obtained in the northeastern part of the Pacific.