The net photosynthetic production of oxygen is 10 x 10-7mL O2 cm-2 s-1 in a turb

Question

The net photosynthetic production of oxygen is 10 x 10-7mL O2 cm-2 s-1 in a turbulently-mixed region of seawater. If this system is at steady state, then the flux from the water to the atmosphere is equal to the net production rate. This seawater has a steady-state O2 concentration of 8.0 mL O2 L'1 SW even though its saturation concentration is 6.0 mL O2 L-1SW, because it is separated from the atmosphere by a stagnant thin film. Use the diffusion coefficient of O2 at 24 DegreesC of 2.3 x 10-5 cm2 s-1 Compute the thickness of the thin film boundary layer under these conditions. Calculate the apparent piston velocity under these conditions. Draw a diagram to represent this situation. Include the following features: the thin film, the mixed layer and the direction of the O2 flux. Sketch in the depth profile of O2concentrations. Sketch in the upper and lower boundary of the thin film. Indicate the boundary' at which the O2 concentration is 8.0 ml O2 L-1SW and the boundary' at which the O2 concentration is 6.0 ml O2 L-1 SW.

Explanation / Answer

3) we know that

F = - D[A] /Z

where

D is the molecular diffusion coefficient = 2.3 X 10^-5

Z is the thickness of the stagnant film (film) = ?

[A] = 8

F = 10 X 10^-7

So Z = D[A] / F = 2.3 X 10^-5 X 8 / 10 X 10^-7 = 184 cm

b) Apparent piston velocity = D/Z = 2.3 X 10^-5 / 184 = 1.25 X 10^-7

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