Abstract
We collected observations of ocean mixing from three moorings placed at
the 330m, 200m, and 150m isobaths on a pelagic ridge on the Australian
North West Shelf (NWS). The region is subject to energetic surface and
internal tides, non-linear internal waves, flow-topography interactions,
and episodic intense wind events (i.e., tropical cyclones) that
collectively drive energetic diapycnal mixing. We identified five
dominant internal wave categories: both low (time scales from double the
buoyancy period to 4 hours) and high-frequency (time scales between
buoyancy period and double the buoyancy period) mode-1 waves, mode-2
waves, internal bores, and internal hydraulic jumps. A small number of
turbulent mixing events dominated the total vertical heat flux at each
mooring, with 15% of estimates accounting for as much as 90% of the
total observed heat flux. These turbulent mixing events often occurred
during the passage of internal wave events, with the internal wave
events accounting for as much as 60% of the total heat flux in some
locations. High-frequency mode-1 waves were the most significant
contributors to the total vertical heat flux (∼ 20%). Internal bores
made significant but localized contributions to mixing, accounting for
up to ∼ 50% of the total vertical heat flux in some regions but with a
negligible influence elsewhere. The contributions of the different
internal wave categories to the total flux became more heterogeneous at
shallower sites, indicating an increasingly complicated relationship
between the forcing internal wave field and the mixing.