Ocean Radiant Heating. Part I: Optical Influences

Abstract

Radiative transfer calculations are used to quantify the effects of physical and biological processes on variations in the transmission of solar radiation through the upper ocean. Results indicate that net irradiance at 10 cm and 5 m can vary by 23 and 34 W m?2, respectively, due to changes in the chlorophyll concentration, cloud amount, and solar zenith angle (when normalized to a climatological surface irradiance of 200 W m?2). Chlorophyll influences solar attenuation in the visible wavebands, and thus has little effect on transmission within the uppermost meter where the quantity of near-infrared energy is substantial. Beneath the top few meters, a chlorophyll increase from 0.03 to 0.3 mg m?3 can result in a solar flux decrease of more than 10 W m?2. Clouds alter the spectral composition of the incident irradiance by preferentially attenuating in the near-infrared region, and serve to increase solar transmission in the upper few meters as a greater portion of the irradiance exists in the deep-penetrating, visible wavebands. A 50% reduction in the incident irradiance by clouds causes a near 60% reduction in the radiant heating rate for the top 10 cm of the ocean. Solar zenith angle influences transmission during clear sky periods through changes in sea-surface albedo. This study provides necessary information for improved physically and biologically based solar transmission parameterizations that will enhance upper ocean modeling efforts and sea-surface temperature prediction.