Six months of concurrent, co-located physical and bio-optical time series from a moored array deployed in the Sargasso Sea during 1987 have been analyzed by combining standard Fourier analysis techniques with a unique presentation method. The spectral information obtained from the time series analysis covers four orders of magnitude in frequency space. This is especially useful for revealing temporal variations in high frequency variance and the physical/biological interactions that occur at these frequencies. The presentation method used here consists of time/frequency distributions of normalized variance and squared coherence that resulted from the time series analysis. These reveal a seasonal succession of physical/biological interaction mechanisms. It is apparent that the onset, and ongoing development, of water-column stratification initiates an evolution from a regime dominated by horizontal advection, within which phytoplankton act as a passive tracer, to one where physical processes impact the biology on spatial and temporal scales which are consonant with phytoplankton physiology. The observed interactions include: (I) transport of distinct bio-optical properties within advected mesoscale features; (2) significant phytoplankton patchiness associated with the regional evolution of the spring bloom and; (3) high frequency bio-optical variability associated with the interaction of the deep chlorophyll maximum with internal wave motions.
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