Premium
Importance of N 2 fixation vs. nitrate eddy diffusion along a latitudinal transect in the Atlantic Ocean
Author(s) -
Mouriño-Carballido Beatriz,
Graña Rocío,
Fernàndez Ana,
Bode Antonio,
Varela Manuel,
Domínguez J. Francisco,
Escànez José,
de Armas Demetrio,
Marañón Emilio
Publication year - 2011
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2011.56.3.0999
Subject(s) - ocean gyre , new production , nitrate , oceanography , subtropics , eddy diffusion , transect , northern hemisphere , environmental science , photic zone , atmospheric sciences , geology , biology , nutrient , ecology , geography , phytoplankton , turbulence , meteorology
We present ocean, basin‐scale simultaneous measurements of N 2 ‐fixation, nitrate diffusion, and primary production along a south–north transect in the Atlantic Ocean crossing three biogeographic provinces: the south subtropical Atlantic (SSA; ∼ 31°S–12°S), the equatorial Atlantic (EA; ∼ 12°S–16°N), and the north subtropical Atlantic (NSA, ∼ 16°N–9°N) in April–May 2008. N 2 ‐fixation and primary production were measured as 15 N 2 and 14 C uptake, respectively. Dissipation rates of turbulent kinetic energy ( ε ) were measured with a microstructure profiler. The vertical input of nitrate through eddy diffusion was calculated from the product of diffusivity, derived from ε , and the gradient of nanomolar nitrate concentration across the base of the euphotic zone. The mean N 2 ‐fixation rate in EA was 56 ± 49 μmol N m −2 d −1 , whereas SSA and NSA had much lower values (∼ 10 μmol N m −2 d −1 ). Because of the large spatial variability in nitrate diffusion (34 ± 50, 405 ± 888, and 844 ± 1258 μmol N m −2 d −1 in SSA, EA, and NSA, respectively), the contribution of N 2 ‐fixation to new production in the SSA, EA, and NSA was 44% ± 30%, 22% ± 19%, and 2% ± 2%, respectively. The differences between SSA and NSA in the contribution of N 2 fixation were partly due to the contrasting seasonal forcing in each hemisphere, which likely affected both N 2 fixation rates and vertical nitrate diffusion. The variability in the nitrogen budget of the Atlantic subtropical gyres was unexpectedly high and largely uncoupled from relatively constant phytoplankton standing stocks and primary production rates.