Modeling how surface nitrogen fixation influences subsurface nutrient patterns in the North Atlantic. Issue 5 (20th May 2013)

• Record Type: Journal Article
• Authors: Yoshikawa, Chisato; Coles, Victoria J.; Hood, Raleigh R.; Capone, Douglas G.; Yoshida, Naohiro
• Is Part Of: Journal of geophysical research. Volume 118:Issue 5(2013:May)
• Page Start: 2520
• Page End: 2534
• Publication Date: 2013-05-20
• Subjects: nutrient patterns -- nitrogen fixation -- North Atlantic; Oceanography -- Periodicals; 551.4605
• DOI: 10.1002/jgrc.20165
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: [1] We represented mechanistically the process of nitrogen (N) fixation and associated N* anomalies in the Atlantic Ocean using a three‐dimensional coupled physical/biogeochemical model. Available direct measurements of N fixation rates in the Atlantic Ocean are compiled, and these, along with observed N* anomalies, constrain the model. The model N fixation rate for the whole Atlantic domain is 2.1 × 10 12 molN yr –1 . The model‐generated N* anomaly shows the observed feature of a subsurface maximum. When plotted on isopycnal surfaces, the model‐generated N* anomaly bears little relation to the pattern of N fixation at the surface. However, the highest N fixation rates should be spatially related to N* distribution if particulate export is remineralized at depths in the same region where the N fixation occurred. We performed case studies varying remineralization and advection to clarify the genesis of the N* anomaly and to determine the reasons underlying differences between N* anomalies and N fixation rate patterns. These studies indicated that the difference between these two patterns was created by both horizontal advection of excess N compared to phosphorus (P) and preferential remineralization of P compared to N. N fixation and preferential P remineralization create high N* anomalies both at the surface and in subsurface waters in the tropical Atlantic, which are transported into the northwestern North Atlantic by western boundary currents and subsequently subducted. As a result, the highest N* anomalies are located not in the tropics but in the northwestern North Atlantic. Key Points: Nitrogen fixation creates high N* anomalies Horizontal advection influences nutrient patterns Preferential phosphorus remineralization influences nutrient patterns