Ocean emissions are estimated to account for 30-40% of the natural sources of nitrous-oxide (N₂O) to the atmosphere (Tian et al. 2020, 2024).  Such estimates are often derived from global ocean biogeochemistry models and Earth System Models that include parameterizations of oceanic N₂O production and consumption processes. The representation of the marine N₂O cycle in these models has evolved in complexity over recent decades as more biogeochemical observations and process rate information has become available to better characterize marine N₂O production and consumption from nitrification and denitrification pathways, especially in the key low oxygen zones of the Eastern Equatorial Pacific and Northern Indian oceans.   Early-stage global ocean biogeochemistry models employed simple empirical parameterizations linking ocean N₂O production to organic matter remineralization and oxygen utilization. Recent model developments include more detailed process-based representation of N₂O production and consumption pathways within the broader marine nitrogen cycle.
The Global Carbon Project’s  (GCP) N₂O Budgets of Tian et al. (2020, 2024) have provided estimates of ocean N₂O emissions from global ocean models as part of their quantification of N₂O sources to the atmosphere.  A third Global N₂O Budget compilation (Tian et al. in prep.) is now underway. This presentation will focus on the current status and recent developments in the numerical modelling of ocean N₂O and also report on the  ocean model analyses compiled for the third GCP N₂O Budget. We will compare  results from current global ocean models to air-sea ocean N₂O flux estimates derived  from surface ocean data, and discuss key uncertainties and directions for future model development in the context of a changing global ocean under increasing pressure from anthropogenic  impacts and climate change.

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