TY - JOUR
T1 - Data-based estimates of suboxia, denitrification, and N2O production in the ocean and their sensitivities to dissolved O2
AU - Bianchi, Daniele
AU - Dunne, John P.
AU - Sarmiento, Jorge Louis
AU - Galbraith, Eric D.
N1 - Publisher Copyright:
© 2012 by the American Geophysical Union.
PY - 2012/5/2
Y1 - 2012/5/2
N2 - Oxygen minimum zones (OMZs) are major sites of fixed nitrogen removal from the open ocean. However, commonly used gridded data sets such as the World Ocean Atlas (WOA) tend to overestimate the concentration of O2 compared to measurements in grids where O2 falls in the suboxic range (O2 < 2-10 mmol m–3), thereby underestimating the extent of O2 depletion in OMZs. We evaluate the distribution of the OMZs by (1) mapping high-quality oxygen measurements from the WOCE program, and (2) by applying an empirical correction to the gridded WOA based on in situ observations. The resulting suboxic volumes are a factor 3 larger than in the uncorrected gridded WOA. We combine the new oxygen data sets with estimates of global export and simple models of remineralization to estimate global denitrification and N2O production. We obtain a removal of fixed nitrogen of 70 ± 50 Tg year–1 in the open ocean and 198 ± 64 Tg year–1 in the sediments, and a global N2O production of 6.2 ± 3.2 Tg year–1. Our results (1) reconcile water column denitrification rates based on global oxygen distributions with previous estimates based on nitrogen isotopes, (2) revise existing estimates of sediment denitrification down by 1/3d through the use of spatially explicit fluxes, and (3) provide independent evidence supporting the idea of a historically balanced oceanic nitrogen cycle. These estimates are most sensitive to uncertainties in the global export production, the oxygen threshold for suboxic processes, and the efficiency of particle respiration under suboxic conditions. Ocean deoxygenation, an expected response to anthropogenic climate change, could increase denitrification by 14 Tg year–1 of nitrogen per 1 mmol m– 3 of oxygen reduction if uniformly distributed, while leaving N2O production relatively unchanged.
AB - Oxygen minimum zones (OMZs) are major sites of fixed nitrogen removal from the open ocean. However, commonly used gridded data sets such as the World Ocean Atlas (WOA) tend to overestimate the concentration of O2 compared to measurements in grids where O2 falls in the suboxic range (O2 < 2-10 mmol m–3), thereby underestimating the extent of O2 depletion in OMZs. We evaluate the distribution of the OMZs by (1) mapping high-quality oxygen measurements from the WOCE program, and (2) by applying an empirical correction to the gridded WOA based on in situ observations. The resulting suboxic volumes are a factor 3 larger than in the uncorrected gridded WOA. We combine the new oxygen data sets with estimates of global export and simple models of remineralization to estimate global denitrification and N2O production. We obtain a removal of fixed nitrogen of 70 ± 50 Tg year–1 in the open ocean and 198 ± 64 Tg year–1 in the sediments, and a global N2O production of 6.2 ± 3.2 Tg year–1. Our results (1) reconcile water column denitrification rates based on global oxygen distributions with previous estimates based on nitrogen isotopes, (2) revise existing estimates of sediment denitrification down by 1/3d through the use of spatially explicit fluxes, and (3) provide independent evidence supporting the idea of a historically balanced oceanic nitrogen cycle. These estimates are most sensitive to uncertainties in the global export production, the oxygen threshold for suboxic processes, and the efficiency of particle respiration under suboxic conditions. Ocean deoxygenation, an expected response to anthropogenic climate change, could increase denitrification by 14 Tg year–1 of nitrogen per 1 mmol m– 3 of oxygen reduction if uniformly distributed, while leaving N2O production relatively unchanged.
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U2 - 10.1029/2011GB004209
DO - 10.1029/2011GB004209
M3 - Article
AN - SCOPUS:85006757534
SN - 0886-6236
VL - 26
JO - Global Biogeochemical Cycles
JF - Global Biogeochemical Cycles
M1 - GB2009
ER -