Phytoplankton and thermal structure in the upper ocean: Consequences of nonuniformity in chlorophyll profile

Solar irradiance absorption in the upper layers of the ocean is influenced by the concentration of phytoplankton. Nonuniformities in vertical chlorophyll (phytoplankton) distributions lead to nonuniformities in absorption and consequently to variations in local heating. Local heating rate tends to decrease monotonically with increasing depth, but certain vertical distributions of chlorophyll lead to a change of sign of the gradient. Data from an oligotrophic ocean station showed a subsurface maximum of chlorophyll intense enough to allow increased heating on the upper slope of the chlorophyll maximum, with a maximum gradient of 0.003°C d −1 m −1 . It is suggested that the importance of such subsurface heating for augmenting vertical mixing and influencing mixed layer deepening may be greatest in the optically clear, open ocean regions.