Determining the Location and Magnitude of Diapycnal Mixing in the Southern Ocean

Supervisors

Nathan Bindoff (UTas),  Trevor McDougall (CSIRO), Steve Rintoul (CSIRO)

Project Outline

Background and Objectives

Inverse models are used in oceanography to determine things about the ocean that cannot be directly measured. Traditionally the inverse technology has been applied to estimate the transport:- that is to estimate the deep so called "reference level" velocities. In the past few years the inverse modelling technique has been refined to the stage that believable estimates of diapycnal mixing activity can now be obtained. However, these estimates of the strength of diapycnal mixing can to date only be obtained as an average over the area of a "box" whose edges are the cruise tracks and continental boundaries.

We have developed a new inverse technique which adds many more sets of equations to the inversion and potentially has the ability to reveal not only the area-averaged strength of diapycnal mixing but also where this mixing in located. For example, in the Southern Ocean, it is important to determine whether the strong diapycnal mixing that is apparent in existing inverse solutions is occurring only at the southern outcrop of isopycnals or whether it is occurring more generally throughout the ACC. To date the new technique has merely been written down as a theoretical construct, and it needs to be tried on both model output and on atlas data and cruise section data.

The new technique enables several conservation equations to be written for temperature and for salinity for each density layer of a box model whereas to date each layer provided just one such equation for temperature and one for salinity. It is expected that the new technique will better constrain the reference level velocities as well as providing spatial information on the strength of mixing processes. If the project proves as successful as we envisage, it should become the inverse model of choice for inverting cruise data and we would like to see the technique be included in the software package "Do-box". Following this, the technique should be used not simply with a simple pair of ocean sections but with say all the WOCE sections.

Contact

Assoc Prof Nathan Bindoff or tel +61 3 6226 2986