Interannual variability of primary production and dissolved organic nitrogen storage in the North Pacific Subtropical Gyre

• Published in: Journal of Geophysical Research: Biogeosciences Vol. 117; no. G3
• Main Authors: Luo, Ya-Wei, Ducklow, Hugh W., Friedrichs, Marjorie A. M., Church, Matthew J., Karl, David M., Doney, Scott C.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.09.2012; American Geophysical Union
• Subjects: Biological oceanography; Boundary conditions; Chemical oceanography; Data collection; dissolved organic nitrogen; Earth sciences; Earth, ocean, space; Ecosystem models; Exact sciences and technology; interannual variability; Mesoscale activity; Nitrogen; North Pacific Subtropical Gyre; Oceanography; Organic nitrogen; Primary production; Upper ocean; Upwelling; Variability; Hawaii; Pacific Ocean; Polynesia; Oceania; North Pacific; Vertical speed; models; Organic nitrogen; simulation; Time series; recycling; Perturbation; storage; nitrates; variability; Long term; Interannual variation; Mesoscale; upwelling; ecosystems; annual average; Forcing; primary productivity; boundary conditions; export; ocean circulation; Data assimilation
• ISSN: 0148-0227; 2169-8953; 2156-2202; 2169-8961
• DOI: 10.1029/2011JG001830

The upper ocean primary production measurements from the Hawaii Ocean Time series (HOT) at Station ALOHA in the North Pacific Subtropical Gyre showed substantial variability over the last two decades. The annual average primary production varied within a limited range over 1991–1998, significantly increased in 1999–2000 and then gradually decreased afterwards. This variability was investigated using a one‐dimensional ecosystem model. The long‐term HOT observations were used to constrain the model by prescribing physical forcings and lower boundary conditions and optimizing the model parameters against data using data assimilation. The model reproduced the general interannual pattern in the observed primary production, and mesoscale variability in vertical velocity was identified as a major contributing factor to the interannual variability in the simulation. Several strong upwelling events occurred in 1999, which brought up nitrate at rates several times higher than other years and elevated the model primary production. Our model results suggested a hypothesis for the observed interannual variability pattern of primary production at Station ALOHA: Part of the upwelled nitrate input in 1999 was converted to and accumulated as semilabile dissolved organic nitrogen (DON), and subsequent recycling of this semilabile DON supported enhanced primary productivity for the next several years as the semilabile DON perturbation was gradually removed via export. Key Points Interannual variability of primary production was generated by nitrogen supply Excess nitrate input was stored as semilabile dissolved organic nitrogen (DON) Semilabile DON prolonged nitrogen accumulation and elevated primary production