On the variability of the thermohaline circulation in the GFDL coupled model

The ocean component of the Geophysical Fluid Dynamics Laboratory coupled model is used to investigate whether or not the interdecadal variability found in Delworth et al. is an ocean-only mode or a mode of the full coupled system. In particular, it has been previously suggested that the variability in the full coupled model is either 1) an internal ocean mode driven by fixed fluxes (atmospheric annual mean plus flux adjustment), which is made less regular through forcing from atmospheric noise; 2) a consequence of the use of flux adjustments: or 3) an ocean-only mode that is excited by atmospheric noise. Through a series of experiments conducted under fixed-flux boundary conditions it is shown that none of these three hypotheses holds and therefore it is concluded that the interdecadal variability found in Delworth et al. is a mode of the full coupled system.