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| Titel |
Oceanic N2O emissions in the 21st century |
| VerfasserIn |
Jorge Martinez-Rey, Laurent Bopp, Marion Gehlen, Alessandro Tagliabue |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250081478
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| Zusammenfassung |
| Climate change will cause multiple perturbations in ocean biogeochemistry during the next
century. Changes in temperature, carbonate chemistry, salinity and dissolved oxygen
concentration will drive changes which remain highly uncertain, especially in the oceanic
nitrogen cycle. Of particular interest regarding feedbacks to the Earth System are the oceanic
emissions of nitrous oxide. N2O is a powerful greenhouse gas with a residence time of more
than 100 years in the atmosphere. Moreover, N2O has been identified as the leading ozone
depletion emission since 2010.
Oceanic N2O, with an annual contribution of 3.6 Tg N and hence 30% of the total natural
sources, is produced by bacterial processes called nitrification and denitrification. These
processes are enhanced in regions of high productivity, with denitrification occurring where
oxygen concentrations are low, typically below 60 μmol/L. Different parameterizations
for N2O production have been proposed over the past decade and considered by
current ocean biogeochemical models. However, significant uncertainties remain in
particular with respect to the future evolution of N2O production under climate
change.
We implemented several published parameterizations of N2O production into
the biogeochemical model PISCES and estimated the change in N2O production,
inventory and N2O sea-to-air flux between 2005 and 2100, under the high emission
scenario RCP8.5. This approach is complemented by an offline analysis of 8 model
output datasets which contributed to the Coupled Model Intercomparison Project
(CMIP5).
Projections of N2O flux from the ocean to the atmosphere yield a 5% decrease on average
in 2100. North- and southwest basins in the Pacific and Atlantic oceans show the largest
reduction in N2O emissions, while the flux tends to increase in regions where the Oxygen
Minimum Zones (OMZs) are located, i.e., Eastern Tropical Pacific and Bay of Bengal. The
projected expansion of the OMZs, from 6.5 to 8.5 106 km3in our experiments, will be
responsible for a 10% increase in the N2O inventory at the Eastern Tropical Pacific that could
be potentially outgassed.
Two mechanisms are identified as the main drivers for the overall decrease in N2O flux.
On the one hand, there is a weakening of the sequence primary production - export of organic
matter to depth - remineralization of organic matter, and hence N2O production via
nitrification. On the other hand, the increasing stratification slows down the N2O transport
from the ocean interior to the surface.
The consistency of our model experiments with the analysis of other CMIP5 model
projections give robustness to the hypothesis that the two mechanisms proposed -reduction in
export production and increase in stratification- are the main regulators of future oceanic N2O
emissions to the atmosphere. |
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