Ocean mixing is one of the most prominent problems in physical oceanography today.  Mixing maintains the stratification, drives the global overturning circulation, distributes nutrients and larvae for biological productivity and fisheries, redistributes heat, salt, nutrients, and pollutants, and influences climate dynamics and currents.  Many different mechanisms cause mixing, including eddies, wind, tides, biology, intrusions, and double diffusion.  Mixing is commonly divided into horizontal and vertical, with eddies a primary horizontal mixing mechanism and wind and tides vertical mixing mechanisms.  Many of these mechanisms are localized and sporadic making mixing difficult to observe.  Additionally, their wide range of scales makes mixing difficult to simulate.  Although ocean and climate simulations are moving to higher resolution, present resolutions are insufficient to reproduce many mixing mechanisms. Instead sub-grid scale parameterizations are employed to represent mixing.  Consequently, models do not handle mixing well.  Improvement of mixing parameterizations in models is an important and overdue.  To accomplish this, more mixing observations and comparisons against simulations are needed.


Robin Robertson

Research Area

School of Physical , Environmental and Mathematical Science, University of New South Wales at Australian Defence Force Academy


Thu, 29/10/2015 - 3:00pm


RC-4082, The Red Centre, UNSW

Mixing and tidal impacts in the waters off Eastern Australia were investigated using a combination of modeling and observational studies, including two voyages, moorings, gliders, realistic modeling, and process modeling.  Barotropic and baroclinic tides were simulated for the waters off eastern Australia in the Coral and Tasman Seas.  Mixing occurred near the continental slope and rough topography and there was clear evidence of internal tides.  Tides were found to impact the mean current, East Australian Current (EAC), enhancing the mean flow by 1-4 Sv in some regions.  Tides did not appear to impact eddy formation; however they affected both the rotational velocity within the eddy and the eddy propagation. Cyclonic eddies rotated faster with tides and anticyclonic eddies slower.  Cyclonic eddies also propagated faster with tides than without tides.  Tides increased cross-shelf transport of cold waters.  Tides influenced mixing by increasing vertical temperature diffusivities by 10-4 to 10-3 m2 s-1 over portions of the continental slope and over rough topography, particularly in regions near the diurnal critical latitudes (27o-30o).  In conclusion, even the small tides of eastern Australia significantly impacted the circulation and mixing in the region.