Nitrogen uptake and regeneration pathways in the equatorial Pacific: a basin scale modeling study
Author:
Wang X.,Murtugudde R.,Le Borgne R.
Abstract
Abstract. It is well known that most primary production is fueled by regenerated nitrogen in the open ocean. Therefore, studying the nitrogen cycle by focusing on uptake and regeneration pathways would advance our understanding of nitrogen dynamics in the marine ecosystem. Here, we carry out a basin-scale modeling study, by assessing model simulations of nitrate and ammonium, and rates of nitrate uptake, ammonium uptake and regeneration in the equatorial Pacific. Model-data comparisons show that the model is able to reproduce many observed features of nitrate, ammonium, such as the deep ammonium maximum (DAM). The model also reproduces the observed de-coupling of ammonium uptake and regeneration, i.e. regeneration rate greater than uptake rate in the lower euphotic zone. The de-coupling largely explains the observed DAM in the equatorial Pacific Ocean. Our study indicates that zooplankton excretion and remineralization of organic nitrogen play a different role in nitrogen regeneration. Rates of zooplankton excretion vary from &lt0.01 mmol m−3 d−1 to 0.1 mmol m−3 d−1 in the upper euphotic zone while rates of remineralization fall within a narrow range (0.015–0.025 mmol m−3 d−1). Zooplankton excretion contributes up to 70% of total ammonium regeneration in the euphotic zone, and is largely responsible for the spatial variability of nitrogen regeneration. However, remineralization provides a steady supply of ammonium in the upper ocean, and is a major source of inorganic nitrogen for the oligotrophic regions. Overall, ammonium generation and removal are approximately balanced over the top 150 m in the equatorial Pacific.
Publisher
Copernicus GmbH
Reference52 articles.
1. Archer, D., Aiken, J., Balch, W., Barber, D., Dunne, J., Flament, P., Gardner, W., Garside, C., Goyet, C., Johnson, E., Kirchman, D., McPhaden, M., Newton, J., Peltzer, E., Welling, L., White, J., and Yoder, J.: A meeting place of great ocean currents: shipboard observations of a convergent front at 2 degrees N in the Pacific, Deep-Sea Res. Pt. II, 44, 1827–1849, 1997. 2. Ashjian, C. J., Smith, S. L., Flagg, C. N., and Idrisi, N.: Distribution, annual cycle, and vertical migration of acoustically derived biomass in the Arabian Sea during 1994–1995, Deep-Sea Res. Pt. II, 49, 2377–2402, 2002. 3. Aufdenkampe, A. K., McCarthy, J. J., Rodier, M., Navarette, C., Dunne, J., and Murray, J. W.: Estimation of new production in the tropical Pacific, Global Biogeochem. Cy., 15, 101–112, 2001. 4. Aufdenkampe, A. K., McCarthy, J. J., Navarette, C., Rodier, M., Dunne, J., and Murray, J. W.: Biogeochemical controls on new production in the tropical Pacific, Deep-Sea Res. Pt. II, 49, 2619–2648, 2002. 5. Aufdenkampe, A. K. and Murray, J. W.: Controls on new production: the role of iron and physical processes, Deep-Sea Res. Pt. II, 49, 2649–2668, 2002.
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