Far far below

Picture this. Three miles deep below the ocean surface northeast of Samoa, around the 8th parallel south of the equator and the 170th western meridian, In the vicinity of the North Tukelau Trough and just west of the Phoenix islands. The picture below is taken from a 1970 map, and political boundaries have changed since.

Phoenix Islands and North Tukelau Trough
The red lines are shipping routes to Wilsons Promontory (and Pago Pago just to the right of the trough if you could see it) from Honolulu. The dashed line is about four degrees south of the Equator. The 3000 number on the ocean contour is in fathoms (6 feet)

Neptune rages below. Here the cold abyssal waters from Antarctica penetrate through a narrow submarine trough into the warmth of the Northern Pacific. Their progress is interrupted by shallower sills in the trough, and as the submarine current cascades down over the sills, it forms and breaks in huge waves, half a mile high. Now a more detailed picture emerges of the violence and mixing induced here that leaves little trace on the surface above. The picture below is from Alford et al.(2013), doi:10.1002/grl.50684 Fig. 2, the depth here is in meters:
many wonderful things in the deep

As they quote: "The flow over the second sill is hydraulically supercritical, with some layers diving down nearly 1000 m and Froude number -- the ratio of observed flow in the deep layer to the speed of long gravity waves -- well above unity"

Note how the neutral density contours break and fall by a kilometer to the right of the ridge at 225 Km. The velocity colors turn a blood red as the deep southern waters ferociously embrace their northern cousin. The Thorpe velocity profiles are derived by sorting the density contours by magnitude and calculating the anomaly to observation giving a measure of instability. And the quantity epsilon at lower left is a measure of watts generated per cubic kilo of water. the exponent "-6" is not so fearsome until once recalls the multiplier, which is about the total mass of a thousand kilometers cubed ... in kilograms.

The giant in these mixers is the Drake Passage; I await similarly detailed studies from that throat.

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