Photochemistry, mixing and diurnal cycles in the upper ocean

The interplay between ocean photochemistry and surface boundary-layer physics is explored in a range of analytical and numerical process models. For simple systems, key attributes of the photochemical distribution can be expressed in terms of a small number of physical and photochemical scaling factors. A coupled, 1-D photochemical/physical model is used to examine the more general case with finite mixing rates, variable photochemical production and evolving boundary layer depth. Finite boundary layer mixing rates act to increase both the diurnal cycle and mean concentration at the surface, and both these increases are further amplified by coupling between photochemistry and diurnal physics. The daily heating/cooling cycle of the upper ocean can lead to a significant reduction in mixing and boundary-layer depth during the day. Accounting for these effects results in additional surface trapping of photochemically produced species and significant enhancements of the surface diurnal cycle and daily mean. -from Authors