Southern Ocean Ventilation

Figure 1 is a comparison of MOZART results to the seasonal cycle in atmospheric N2O due to Southern Ocean ventilation (N2Ovent) observed at Cape Grim, Tasmania. Black solid line is a MOZART run with the biological N2O ventilation source (Fvent2) predicted by the ocean biogeochemistry model of Jin and Gruber [2003]. The observed seasonal cycle in N2O was derived from a detrended harmonic fit to 10 years of AGAGE atmospheric data at Cape Grim. To estimate N2Ovent, the observed seasonal cycle was corrected for thermal (open cyan circles) and thermal + stratospheric (solid blue circles) influences. The thermal influence was estimated based on Ar/N2 data and the stratospheric influence was estimated based on CFC-12 data. Also shown are MOZART results with the CASA soil source of Potter et al. [1996] (dot-dashed magenta line), which demonstrates that soil sources have a relatively small effect on the seasonality of atmospheric N2O at Cape Grim. This figure, from Nevison et al. [2004], is the first to reproduce observed atmospheric seasonal cycles in N2O using specified surface sources in forward ATM runs. However, the figure also demonstrates the large uncertainty associated with the stratospheric influence on tropospheric N2O seasonal cycles.

Published in: Nevison, C.D., R.F. Keeling, R.F. Weiss, B.N. Popp, X. Jin, L.W. Porter and P.G. Hess, Southern Ocean Ventilation Inferred from Seasonal Cycles of Atmospheric N2O and O2/N2 at Cape Grim, Tasmania, in press Tellus B, 2004.