In marine ecosystems, net primary productivity (NPP) is often calculated per unit volume of water to account for the depth of the photic zone, and is expressed in terms of the mass of carbon fixed.
Which of the following is a correct unit to express this net primary productivity?
g m−2yr−1\text{g m}^{-2} \text{yr}^{-1}g m−2yr−1
g m−3yr−1\text{g m}^{-3} \text{yr}^{-1}g m−3yr−1
g yr m−3\text{g yr m}^{-3}g yr m−3
m3g−1yr−1\text{m}^3 \text{g}^{-1} \text{yr}^{-1}m3g−1yr−1
