Sack Lunch Seminar (SLS)

On Diapycnal Motion Due to Unusual Mixing Processes







The nonlinear equation of state causes a variety of processes leading to the transformation of
water masses. It also stops us from constructing well-defined density surfaces which we can
use to describe ocean circulation. Several of these processes have been known for a long
time but have never been quantified to estimate their importance compared to other physical
processes in the ocean. These processes turn out to be very significant in the Southern
Ocean where they produce a substantial amount of downwelling. Here we show how to construct an optimized approximately neutral surface which is as close as possible to describing the trajectories along which fluid particles move. Even though this surface can not be perfectly neutral at every point, it is very close to the neutral direction. We will quantify the residual error and compare it to the error made when using different density variables. We then use these surfaces to quantify other processes caused by the nonlinear equation of state. Over the last decades many oceanographers have been searching for the 'missing' mixing to return dense water masses back to the surface. A linear equation of state has been used to calculate the amount of turbulent mixing which is needed to return these water masses to the surface and recently oceanographers have been looking for regions of increased turbulent
mixing and other processes to do so. But how much 'missing' mixing do we need if we
account for the nonlinear equation of state and the physical processes it causes?