Phytoplankton production in the Sargasso Sea as determined using optical mooring data

Abstract

Optical measurements from an untended mooring provide high‐frequency observations of in‐water optical properties and permit the estimation of important biological parameters continuously as a function of time. A 9‐month time series, composed of three separate deployments, of optical data from the BIOWATT 1987 deep‐sea mooring located in the oligotrophic waters of the Sargasso Sea at 34°N, 70°W are presented. These data have been tested using several bio‐optical models for the purpose of providing a continuous estimate of phytoplankton productivity. The data are discussed in the context of contemporaneous shipboard observations and for future ocean color satellite observations. We present a continuous estimation of phytoplankton productivity for the 9‐month time series. 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, and to compare our bio‐optical observations with concurrent physical observations. The bio‐optical features show variation in response to physical forcings including diel variations of incident solar irradiance, episodic changes corresponding to wind forcing, variability caused by advective mesoscale eddy events in the vicinity of the mooring, and seasonal variability corresponding to changes in solar radiation, shoaling of the mixed layer depth, and succession of phytoplankton populations.