An oceanographer is measuring the net primary productivity (NPP\text{NPP}NPP) of a pelagic phytoplankton community within the photic zone.
Which of the following is a suitable unit to express this productivity in terms of energy per unit volume of the aquatic ecosystem?
kJ year−1 m−2\text{kJ year}^{-1}\text{ m}^{-2}kJ year−1 m−2
kJ year m−3\text{kJ year m}^{-3}kJ year m−3
kJ year−1 m−3\text{kJ year}^{-1}\text{ m}^{-3}kJ year−1 m−3
m3 kJ−1 year−1\text{m}^3\text{ kJ}^{-1}\text{ year}^{-1}m3 kJ−1 year−1