Evaluation of new production in the tropical and subtropical oligotrophic ocean

Abstract

Tropical and subtropical oligotrophic oceanic regions comprising approximately 60% of the entire ocean and new productions in this vast region is vital in understanding the oceanic biogeochemical cycles. Sources of new nitrogen include three processes; allochthonous nitrate supply into the euphotic zone, N_2 fixation, and atmospheric deposition. The present study reviewed processes related to the new production in the tropical and subtropical oligotrophic regions, and discussed future studies on the new production. The new production is controlled not only by diapycnal nitrate flux that is conventionally believed as a main source of the new production, but also by previously overlooked processes including wind-induced mixing and N_2 fixation that vary in time and space. Recent studies indicate that nitrification within and just below the euphotic zone are not negligible, and hence, the new production based on nitrate uptake tends to be overestimated. Evaluation of new production in the tropical and subtropical oligotrophic oceanic regions depends on further understanding the temporal-spatial variation of the nitrogen-input processes to the euphotic zone.