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Carbon‐Based Estimate of Nitrogen Fixation‐Derived Net Community Production in N‐Depleted Ocean Gyres
Author(s) -
Ko Young Ho,
Lee Kitack,
Takahashi Taro,
Karl David M.,
Kang SungHo,
Lee Eunil
Publication year - 2018
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2017gb005634
Subject(s) - alkalinity , phytoplankton , environmental science , ocean gyre , dissolved organic carbon , nitrogen , new production , carbon cycle , nitrate , ocean acidification , advection , mixed layer , carbon fibers , saturation (graph theory) , reactive nitrogen , atmospheric sciences , environmental chemistry , nutrient , chemistry , oceanography , climate change , ecosystem , ecology , subtropics , geology , biology , thermodynamics , physics , organic chemistry , materials science , mathematics , composite number , composite material , combinatorics
Accurate estimation of net community production (NCP) in the ocean is important for determining the future trend for carbon dioxide concentrations in the atmosphere and thus for understanding the global carbon cycle and climate change. Most methods for measuring NCP rely on analysis of dissolved fixed inorganic nitrogen species (N), which are believed to be limiting factors for NCP. However, in the vast areas of the ocean gyres only low levels of N are available for phytoplankton during much of the year. In this study the NCP was estimated by summing the seasonal reduction in the concentration of dissolved inorganic carbon (C T ) in the surface mixed layer, corrected for changes associated with salinity variation, net air‐sea CO 2 flux, horizontal C advection, non‐Redfield diffusive C and N fluxes (deviations from the C:N ratio of 7), and anthropogenic nitrogen deposition. The mixed layer reduction in C T was calculated from an annual C T cycle, deduced from comprehensive records of surface pCO 2 and total alkalinity, using an established thermodynamic model. This method yielded a value of 0.6 ± 0.2 Pg of C, which represents the NCP that occurred during the warming period (approximately 8 months) in the nitrate‐depleted (<0.2 μmol/kg) ocean. Our estimate is broadly consistent with the global N 2 fixation rate estimated using the 15 N‐based method and suggests that N 2 fixation by microorganisms is a major driver for this NCP.