Paulmier1,
A., D. Ruiz-Pino1, L. Farias2, O. Ulloa2 and
A. Poisson1
1LBCM,
Université Curie, courrier 134, 4 pl. Jussieu 75005 Paris, France, Tel: +33144274861, Fax:
+33144274993, E-mail: paulmier@ccr.jussieu.fr and 2COPAS,
Universidad de Concepción, Concepción, Chile
How the Oxygen Minimum Zone (OMZ)
could affect CO2-N2O fluxes? Observation/modelling
The OMZ extension -taking place
between cold/warm periods- could play a feedback effect on atmospheric CO2-N2O
which remains unknown. The approach consists in:
- first simultaneous CO2-N2O
observations in the East South Pacific OMZ (4 cruises + monthly monitoring
during 2000-2001);
- two new conceptual biogeochemical
modellings (O2 consumption above the OMZ; Organic Matter (OM)
remineralization in the OMZ).
Both CO2-N2O
(up to 2700 umol/kg - 120 nmol/kg) are actively produced at the oxycline of the
OMZ. These two production indicate 2 behaviors, observable in both
profiles/fluxes:
i) CO2 mode (coupling:
simultaneous CO2-N2O source) associated to a strong oxic
OM remineralization;
ii) N2O mode (decoupling:
CO2 sink, high N2O production-source) associated to a OM
preservation.
The O2 consumption
modelling suggests that the OM input is able to trigger the shift between the
remineralization (CO2) and preservation(N2O) modes.
Moreover, using in addition the OMZ remineralization modelling, the CO2
and N2O modes correspond to observable features: thin and thick OMZ,
high and low Primary Production (PP), respectively. The sub-Milankovitch scales
confirm the CO2 and N2O modes, corresponding to the OMZ
formation and establishment respectively during the cold-warm transition.
Therefore, the high N2O monitoring in the current/future OMZ would
allow to detect the OMZ establishment and the CO2/N2O
decoupling, i.e., a sink effect for CO2. Moreover if the homeostasia
between PP-OMZ is further confirmed, as suggested by the results:
i) the ocean would never become
totally anoxic;
ii) PP-OMZ would control the CO2atm-N2Oatm natural variations interval, due to the oceanic activity.