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Modeling how surface nitrogen fixation influences subsurface nutrient patterns in the North Atlantic
Author(s) -
Yoshikawa Chisato,
Coles Victoria J.,
Hood Raleigh R.,
Capone Douglas G.,
Yoshida Naohiro
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20165
Subject(s) - advection , geology , remineralisation , oceanography , biogeochemical cycle , redfield ratio , nutrient , fixation (population genetics) , chemistry , phytoplankton , environmental chemistry , biology , ecology , physics , inorganic chemistry , fluoride , thermodynamics , biochemistry , gene
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.