The Southern Ocean seasonal cycle of N 2 O, an atmospheric modelling study.

  • Louis Byrne

Student thesis: Master's ThesisMaster of Science by Research (MScR)


The seasonal cycle of N 2 O in the Southern Ocean is produced by the thermal in and out-gassing of N 2 O driven by changes in temperature and the wind driven ventilation of surface waters due to vertical mixing processes. Previous studies have used atmospheric data from an AGAGE (Advanced Global Atmospheric Gases Experiment) site in Cape Grim, Tasmania, to investigate how these processes affect the seasonal N 2 O source in the Southern Ocean, however, the impact of land fluxes on the N 2 O signal at Cape Grim remains unaccounted for.
This study utilises a global biogeochemical model of the marine N 2 O source as well as the NAME (Numerical Atmospheric Modelling Enivronment) atmospheric particle dispersion model to evaluate the ocean model’s prediction of atmospheric concentration changes due to oceanic fluxes of N 2 O near Cape Grim. Data are filtered to remove periods of high land influence using the NAME model output. Scaling factors are calculated for each month of data between 2008 and 2013 via an orthogonal distance regression analysis. Additionally, the biogeochemical model has been run using
two gas exchange parameterisations, to investigate how varying parameterisations of gas exchange affects the results of the analysis.
On average, this analysis found a good agreement between the predicted marine N 2 O source and measured atmospheric mole-fractions during periods of high marine influence, although there were large inter-annual variations that remain unexplained. Neither the Wanninkhov 92 or Krakaur gas exchange parameterisations produced a significant difference in the results, although the uncertainty was slightly lower using the Krakaur parameterisation. These results support the view of Nevison et al. (2005), that Southern Ocean ventilation is largely responsible for the seasonal cycle in the marine N 2 O source in the Southern Ocean, and that this process is one component of the seasonal N 2 O cycle at Cape Grim, however, significant discrepancies in the inter-annual variations suggest that more work is needed to have a complete understanding the Southern Ocean N 2 O source
Date of Award23 Jan 2019
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMatthew L Rigby (Supervisor) & Anita L Ganesan (Supervisor)

Cite this