Thermocline diurnal

The previous section showed how mixing processes determine the way UML constituents (molecules or organisms) enter the photoactive zone where they may participate in a UVR-mediated process. Under strong stratification, such transport is very limited, so UVR effects will only involve those constituents already present in the active zone. Such extreme stratification can be episodically important in systems where diurnal thermoclines form, but more typically the UML extends below the photoactive zone so that constituents in waters below the photoactive zone will also participate in UVR photochemistry and photobiology. The mixing characteristics of the UML influence photoprocesses in at least two fundamental ways. First, the depth of the UML influences the average UVR exposure that occurs second, the rate of vertical transport, either due to... 

Figure 3. Schematic of the time vs. depth distribution of floats released at various times during a diel cycle of nocturnal mixing and diurnal stratification in the Labrador Sea [E. D Asaro and G. Dairiki unpublished data as shown in 2]. The heavy line (a composite of three separate float deployments) depicts a possible depth history of a non-motile plankton over the 24 h period. Note that trajectories are terminated once they enter the stable diurnal thermocline since they actually start to ascend due to very slight positive buoyancy of the floats.

J. Mourn, D. Caldwell, C. Paulson (1989). Mixing in the equatorial surface layer the diurnal thermocline. J. Geophys. Res., 94,2005. 

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