New primary production and nitrification in the western subtropical North Atlantic: a modeling study

The original definition of new primary production rests on the assumption that nitrogenous substrate taken up to fuel algal growth is coming into contact with phytoplankton for the first time that year. Therefore, should the generation of nitrate from ammonium by nitrification turn out to be significant in surface waters then nitrate uptake can no longer be simply ascribed to new production. A modeling study is presented centered on the Bermuda Atlantic Time-series Station, in the oligotrophic subtropical North Atlantic. We quantify the role of nitrification in providing nitrate to fuel primary production through a full annual cycle for the first time. The results confirm previous limited observations suggesting that a major fraction of nitrate uptake in oligotrophic regions (where nitrification will be most influential), previously ascribed to new production, may actually involve “recycled” nitrate.