Do Nitrogen Transformations in the Poleward Undercurrent off Peru and Chile Have a Globally Significant Influence?
Although it represents only about 0.01% of the total oceanic volume, the Poleward Undercurrent off the coasts of Peru and northern Chile is the site of globally significant nitrogen transformations. The cooccurrence of oxygen deficient (<~0.05 m1/1) waters and high fluxes of organic material causes the regional denitrification rate to comprise about 20% of the total marine rate and most of this occurs within the Undercurrent. Theoretical considerations and the existence of extremely low and extremely high nitrous oxide concentrations in and near the Undercurrent suggest that nitrous oxide turnover in this region occurs at much higher rates than in the “average ocean.”
The processes of denitrification and nitrous oxide turnover are of more than casual interest. Denitrification converts combined nitrogen into nitrogen gas which is unavailable to most plants. Therefore, this nitrogen transformation can limit the ocean’s ability to sequester atmospheric carbon dioxide. Changes in nitrous oxide cycling in regions such as the Poleward Undercurrent could significantly affect the rate at which nitrous oxide is being added to the atmosphere. This gas contributes significantly to the “greenhouse effect” and is the main source of nitrogen oxides in the stratosphere.
The advective field associated with the Poleward Undercurrent exerts a major control on the supply of oxygen to the subsurface waters off the coasts of Peru and Chile, and helps to establish counter-current systems that can create concentrations of organic material. Since the nitrogen transformations described above are sensitive to both oxygen levels and the supply of organic material, understanding these processes requires an understanding of the dynamics of the Poleward Undercurrent.
KeywordsNitrous Oxide Nitrogen Cycle Denitrification Rate Atmospheric Carbon Dioxide Photic Zone
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