Spatial heterogeneity of the planktonic fields in the upper mixed layer of the open ocean

Field surveys were conducted in the open ocean regions of the Indian and Atlantic Oceans and the Mediterranean (Adriatic) Sea. Continuous records were taken along transects of several hundreds of km over the area. Zooplankton and chlorophyll a (chl a) samples were collected from the surface layer using a high capacity pump while the ship was underway. The quantitative trends of occurrence of zooplankton biomass of different patch sizes over the studied areas were quite similar. From the averaged trend and non-linear regression analysis, it was demonstrated that on a scale of tens to hundreds of km the number of patches exponentially diminishes with patch size. The power spectra of temperature, chl a and zooplankton biomass in the surface layer were similar. They monotonically decrease with the decrease of the spatial wavelength of oscillations of the above parameters. The typical slope of the spectra of temperature, phytoplankton and zooplankton fields are within the range of -3 to -2 in a band of wavelengths from 200 to 10 km. In the western subtropical Atlantic where the internal waves are well developed in the seasonal thermocline layer, the variability of zooplankton biomass was characterised by a power spectra having several local peaks of spatial spectral density on a background of a declining curve. Nevertheless, the average spectra slope exhibits the same trend, that is, it diminishes with the slope of the curve within the range -3 to -2. Temperature and zooplankton biomass spectra exhibited coherent local peaks of spectral density at similar wavelengths.