Net Oxygen Consumption
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Assume that the initial oxygen concentration of a water mass when it existed at the surface was [O2]0, and that the water mass has moved to a depth of 3000 m. We then conducted oceanographic observations and sampled water at a depth of 3000 m to measure oxygen concentrations [O2 3000 m]. The amount of oxygen consumed by respiration during the movement of that water mass to 3000m is determined by the formula [O2 consumed by respiration] = [O2]0 - [O2 3000m].
Once the atmospheric oxygen concentration (a constant value) and water temperature are determined, [O2]0 can be calculated.
Let us estimate the amount of oxygen (ΔO2) consumed by respiration between time t =0 and t=T.
ΔO2 = 【O2】t=0 －【O2】t=T
where 【O2】t is the oxygen concentration at time t.
In the actual ocean, How should we define. How should we define 【O2】t=0 and 【O2】t=T?
One should be able to take exactly the same water samples at different times and measure the oxygen concentration.
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The other is an area with a constant flow of water, where water upstream and downstream can be collected in a short period of time.
We can expect the oxygen concentration in the ocean surface water to have reached equilibrium with the atmosphere, so we take that equilibrium state as the initial value of oxygen concentration, [O2]0. Once the surface water is removed from contact with the atmosphere, the oxygen concentration will continue to decrease thereafter due to oxygen consumption in the ocean water. Although the elapsed time is unknown, the amount of oxygen consumption can be determined by measuring the oxygen concentration in the seawater.
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