Southern Ocean ventilation inferred from seasonal cycles of atmospheric N2O and O2/N2 at Cape Grim, Tasmania

• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2004
• Subjects: Grim; Southern Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.488.8682; http://www.soest.hawaii.edu/GG/FACULTY/POPP/Nevison et al 2005 Tellus B.pdf

The seasonal cycle of atmospheric N2O is derived from a 10-yr observational record at Cape Grim, Tasmania (41◦S, 145◦E). After correcting for thermal and stratospheric influences, the observed atmospheric seasonal cycle is consistent with the seasonal outgassing of microbially produced N2O from the Southern Ocean, as predicted by an ocean bio-geochemistry model coupled to an atmospheric transport model (ATM). The model–observation comparison suggests a Southern Ocean N2O source of ∼0.9 Tg N yr−1 and is the first study to reproduce observed atmospheric seasonal cycles in N2O using specified surface sources in forward ATM runs. However, these results are sensitive to the ther-mal and stratospheric corrections applied to the atmospheric N2O data. The correlation in subsurface waters between apparent oxygen utilization (AOU) and N2O production (approximated as the concentration in excess of atmospheric equilibrium N2O) is exploited to infer the atmospheric seasonal cycle in O2/N2 due to ventilation of O2-depleted subsurface waters. Subtracting this cycle from the observed, thermally corrected seasonal cycle in atmospheric O2/N2 allows the residual O2/N2 signal from surface net community production to be inferred. Because N2O is only produced in subsurface ocean waters, where it is correlated to O2 consumption, atmospheric N2O observations provide a method-ology for distinguishing the surface production and subsurface ventilation signals in atmospheric O2/N2, which have