Optical measurements from an untended mooring provide high-frequency observations of in-water optical properties and permit the continuous estimation of important biological parameters. A 9-month time series of optical data, composed of three separate deployments, from the Biowatt 1987 deep-sea mooring located in the oligotrophic waters of the Sargasso Sea at 32 ¿N, 70 ¿W, is presented. These data have been analyzed using several bio-optical models for the purpose of providing a continuous estimate of the spectral diffuse attenuation coefficient and pigment biomass. Results from the first 70-day deployment are emphasized to demonstrate the utility of optical observations as proxy measures of biological parameters, to present preliminary analysis of the temporal variations, and to intercompare our bio-optical observations with concurrent physical observations. Bio-optical properties exhibit variation in response to physical forcings, such as diel variations of incident solar irradiance, episodic wind forcing, advective mesoscale eddy events, seasonal variability corresponding to changes in solar radiation, the shoaling of the mixed layer depth, and succession of phytoplankton populations. The mooring data are discussed in the context of contemporaneous shipboard observations as well as in terms of future ocean color satellite observations. ¿ American Geophysical Union 1991