New production

These forms are utilised by autotrophic phytoplankton to synthesise organic molecules such as amino acids (the building blocks of proteins).

This is performed by different bacteria in two stages : NH3 + O2 → NO2− + 3H+ + 2e− NO2− + H2O → NO3− + 2H+ + 2e− Crucially, this process is believed to only occur in the absence of light (or as some other function of depth).

In the ocean, this leads to a vertical separation of nitrification from primary production, and confines it to the aphotic zone.

This leads to the situation whereby any nitrate in the water column must be from the aphotic zone, and must have originated from organic material transported there by sinking.

Primary production fuelled by nitrate is, therefore, making use of a "fresh" nutrient source rather than a regenerated one.