Depth variations in the attenuation coefficient for light in the ocean were calculated using a one-parameter model based on the chlorophyll-a concentration C_c and experimentally-determined Gaussian chlorophyll-depth profiles. The depth profiles were related to surface chlorophyll levels for the range 0-4 mg/m~2, representing clear, open ocean. The depth where C_c became negligible was calculated to be shallower for places of high surface chlorophyll; 111.5 m for surface chlorophyll 0.8 < C_c < 2.2 mg/m~3 compared with 415.5 m for surface C_c < 0.04 mg/m~3. Below this depth is the absolute minimum attenuation for underwater ocean communication links, calculated to be 0.0092 m~(-1) at a wavelength of 430 nm. By combining this with satellite surface-chlorophyll data, it is possible to quantify the attenuation between any two locations in the ocean, with applications for low-noise or secure underwater communications and vertical links from the ocean surface.
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