Meridional variability of the vertical structure and air–sea fluxes of N 2O off central Chile (30–40°S)

Abstract

The spatial variability of the N 2O in the coastal band off central eastern South Pacific (30–40°S) was evaluated during the upwelling season (austral spring and summer). Herein, we interpreted the observed meridional pattern in terms of hydrographic vertical structure (water mass composition and fresh water contribution), wind patterns (as upwelling events) and topography (wide of the continental shelf) of the region. Consequently, three meridional provinces were determined: north central Chile (NCC), central central Chile (CCC) and south central Chile (SCC). The surface layer was most of the time a source of N 2O towards the atmosphere but it showed a great meridional variability (from −23.1 to 395 μmol m −2 d −1). The strongest air–sea N 2O fluxes were quantified at CCC, area subjected to strong upwelling and described as high chlorophyll zones, whereas the slighter air-sea N 2O fluxes were estimated at SCC, where a high freshwater contribution was observed. The presence of continental shelf at CCC intensified the subsurface N 2O production pattern associated with high biomass which in turn consume oxygen. In fact, the highest N 2O accumulation occurred within the oxycline and the OMZ core respect to the surface layer. This accumulation decreases from the NCC to the SCC. According to the N 2O spatial scaling, the coastal area (∼41,105 km 2) contributes about 12.78 Gg resulting in an important source of N 2O that should be considered in the global balance of atmospheric nitrous oxide.