The oxygen minimum zone (OMZ) off Chile as intense source of CO2 and N2O
Résumé
The oxygen minimum zones (OMZs) are recognized as intense sources of N2O greenhouse gas (GHG) and could also be potential sources of CO2 , the most important GHG for the present climate change. This study evaluates, for one of the most intense and shallow OMZ, the Chilean East South Pacific OMZ, the simultaneous N2O and CO2 fluxes at the air-sea interface. Four cruises (2000-2002) and 1 year of monitoring (21°-30°-36°S) off Chile allowed the determination of the CO2 and N2O concentrations at the sea surface and the analysis of fluxes variations associated with different OMZ configurations. The Chilean OMZ area can be an intense GHG oceanic local source of both N2O and CO2. The mean N2O fluxes are 5-10 times higher than the maximal previous historical source in an OMZ open area as in the Pacific and Indian Oceans. For CO2 , the mean fluxes are also positive and correspond to very high oceanic sources. Even if different coupling and decoupling between N2O and CO2 are observed along the Chilean OMZ, 65% of the situations represent high CO2 and/or N2O sources. The high GHG sources are associated with coastal upwelling transport of OMZ waters rich in N2O and probably also in CO2 , located at a shallow depth. The integrated OMZ role on GHG should be better considered to improve our understanding of the past and future atmospheric CO2 and N2O evolutions.