Sea-to-air and diapycnal nitrous oxide fluxes in the eastern tropical North Atlantic Ocean

[摘要] Sea-to-air and diapycnal fluxes of nitrous oxide (N₂O) into the mixedlayer were determined during three cruises to the upwelling region offMauritania. Sea-to-air fluxes as well as diapycnal fluxes were elevatedclose to the shelf break, but elevated sea-to-air fluxes reached furtheroffshore as a result of the offshore transport of upwelled water masses. Tocalculate a mixed layer budget for N₂O we compared the regionallyaveraged sea-to-air and diapycnal fluxes and estimated the potentialcontribution of other processes, such as vertical advection and biologicalN₂O production in the mixed layer. Using common parameterizations forthe gas transfer velocity, the comparison of the average sea-to-air anddiapycnal N₂O fluxes indicated that the mean sea-to-air flux is aboutthree to four times larger than the diapycnal flux. Neither vertical andhorizontal advection nor biological production were found sufficient toclose the mixed layer budget. Instead, the sea-to-air flux, calculated usinga parameterization that takes into account the attenuating effect ofsurfactants on gas exchange, is in the same range as the diapycnal flux.From our observations we conclude that common parameterizations for the gastransfer velocity likely overestimate the air-sea gas exchange within highlyproductive upwelling zones.

[学科分类] 地球化学与岩石