HR: 1340h
AN: OS13B-0535    [Abstracts]
TI: Constraining Oceanic N$_2$O Production Mechanisms by an Inversion of Large-Scale Oceanic N$_2$O Data
AU: * Jin, X
EM: xjin@igpp.ucla.edu
AF: IGPP and Department of Atmospheric and Oceanic Sciences, UCLA, 3845 SLICHTER HALL, Los Angeles, CA 90095-1567 United States
AU: Gruber, N
EM: ngruber@igpp.ucla.edu
AF: IGPP and Department of Atmospheric and Oceanic Sciences, UCLA, 3845 SLICHTER HALL, Los Angeles, CA 90095-1567 United States
AU: Nevison, C D
EM: nevison@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80307-3000 United States
AB: The ocean is a main source of atmospheric N$_2$O, an important greenhouse gas with a high global warming potential (GWP). N$_2$O is produced in the ocean through two pathways: one is associated with nitrification, i.e. the conversion of ammonium to nitrate during the remineralization of organic nitrogen; the other is associated with low oxygen concentration and likely involves a not well understood coupling between nitrification and denitrification. We refer to the latter as the low oxygen pathway. These two mechanisms have very different characteristics. The nitrification pathway occurs throughout the ocean in the main thermocline and has a yield of only about 1 in 1000, i.e. 1 molecule of N$_2$O is produced per thousand molecules of NH$_4$ entering nitrification. In contrast, the low oxygen pathway has very high yields, but occurs only in a few low oxygen regions located mainly in the tropics and in coastal ocean. These differences result in the two mechanisms having very different responses to environmental changes. For example, Jin and Gruber (2003) showed recently that the two different mechanisms lead to very different offsetting effects when the ocean is fertilized with iron to reduce atmospheric CO$_2$. However, the relative importance of these two mechanisms is still not well known. We model these two mechanisms separately in a global-scale biogeochemical model into which we have added the N$_2$O cycle based on the work of Suntharalingam et al.(2000). We then constrain the relative importance by using inversion methods, taking advantage of a new global data-set of oceanic N$_2$O observations. Our initial results show that about half of the N$_2$O in the ocean is produced by nitrification pathway and the other half by the low oxygen pathway.
DE: 4805 Biogeochemical cycles (1615)
DE: 4808 Chemical tracers
DE: 4815 Ecosystems, structure and dynamics
DE: 4255 Numerical modeling
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting