Understanding of solar energy transmission is important for quantification and modeling of ocean radiant heating and primary productivity. Solar transmission and ocean radiant heating affect the intensity and depth of upper water column stratification. Stratification can impact upper ocean ecology by limiting or facilitating vertical motion of phytoplankton; nutrient entrainment and availability; and movement of riverine inputs, suspended matter, and pollutants. The variability of solar transmission is dependent on the in-water spectral solar attenuation coefficient and the sea surface albedo, which are both influenced by meteorological and upper ocean physical processes, and bio-optical parameters. Past experimental and modeling studies of ocean radiant heating and solar transmission have primarily been executed for the open ocean. Studies regarding the impacts of coastal ocean processes on solar transmission have been limited until recently.

An extensive physical and bio-optical time series data set, coupled with radiative transfer simulations, is used to characterize the processes and parameters that contribute to the variability of spectral solar transmission, sea surface albedo, and upper ocean radiant heating rates (RHR) in coastal waters. The data were collected from a mooring off the east coast of the United States in 24 m water depth in summer 2001. Three different analyses are utilized: (1) time series statistical analyses; (2) examination of processes and parameters affecting solar transmission, sea surface albedo, and RHR using radiative transfer simulations; and (3) investigation of bio-optical effects on RHR and heat content.

(1) Quantitative coherence analyses suggest that cloud cover, chlorophyll concentration, and colored dissolved organic matter (CDOM) have the greatest impacts on solar transmission in the upper ocean in the visible wavelengths. All of these parameters are significantly coherent (negative phase) with solar transmission on a scale of about 1 week. Empirical orthogonal function (EOF) analyses show that the mixed layer depth (MLD) exhibits the strongest inverse correlation with solar transmission and RHR. (2) Radiative transfer simulations indicate that chlorophyll concentration, followed by absorption and attenuation coefficients, have the most significant impact on solar transmission variability. Solar angle and cloud cover greatly influence sea surface albedo. (3) Our data demonstrate that solar transmission is 14% lower and albedo is 1% higher for waters with higher concentrations of chlorophyll (~5 µg l^-1) as compared with lower chlorophyll concentration (~1 µg l^-1). In addition, the heat content of the upper mixed layer can increase by orders of magnitude during periods of deep mixing. For a shallow mixed layer (2 m), the mean hourly heat content is 90 W m^-2 as compared to 280 W m^-2 for a deeper mixed layer (6 m).