The evolution of bio-optical and physical properties of the upper layer of the open ocean has been examined at time scales from a few minutes to several months using recently developed multi-variable moored systems (MVMS). Concurrent, colocated time series measurements of horizontal currents, temperature, photosynthetically available radiation, transmission of a beam of collimated light (660 nm), stimulated chlorophyll fluorescence, and dissolved oxygen concentration were made. The systems were located at eight depths in the upper 160 m of the Sargasso Sea (34 ¿N, 70 ¿W) and were deployed three times for a total of 9 months in 1987. The first deployment data presented here show considerably more variability than those of the latter two deployments because of the dynamic springtime shoaling of the mixed layer and the accompanying phytoplankton bloom and more mesoscale variability associated with cold core rings and warm outbreak waters associated with the Gulf Stream. These data are used to demonstrate the utility of the MVMS and indicate the importance of high-frequency, long-term sampling of bio-optical and physical variables of the upper ocean for understanding and modeling dynamical changes in bio-optical properties, primary production, and carbon fluxes of the upper ocean on time scales ranging from minutes to seasons to decades. Some phenomena observed with the systems include (1) diurnal variations in bio-optical properties, (2) springtime stratification and rapid (~2 days and less) episodic changes in the beam attenuation coefficient and in situ chlorophyll fluoresence, and (3) advective episodes associated with warm outbreaks of Gulf Stream waters and cold core Gulf Stream rings in the vicinity of the mooring. ¿ American Geophysical Union 1991