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For over a century oceanographers and scientists have studied ocean currents, such as the Gulf Stream in the North Atlantic and the Kuroshio current in the North Pacific, noting the effects of such surface currents.
In the last twenty years their attention has included the study of 'ocean cataracts'. These are a direct result of the process of convection - the transfer of heat by bulk motion of water.
Most people know that the highest waterfall in the world is Angel Falls in Venezuela, South America, the water cascading for nearly a kilometre before its spectacular arrival at the bottom.
The Guaira Falls, on the Brazil and Paraguay border, have the largest average flow rate, at 13000 cubic metres a second.
We are all astounded at these incredible figuresabove sea level but less is widely known about what goes on below sea level. For example, it was discovered that, below the Denmark Srait, there is an immense cascade of water that carries five billion cubic metres per second down a descent of three and a half kilometres, dwarfing the Angel Falls and making the Guaira falls flow rate look like a trickle.
Even the awesome Amazon River that flows into the Atlantic Ocean at 200,000 cubic metres a second pales when compared to the Denmark Strait Cataract.
To understand how these ocean cataracts occur, one may think of an ocean in the tropics absorbing the sun and heating up. At the same time, at both Poles, the temperature of the sea water is exceedingly low and, being much denser than the water in the tropics, it has a tendency to sink. This incurs convective currents at the bottom and, from there, the cold water spreads out towards the more temperate areas, displacing the warmer water above it. As a result, this warmer water rises in gentle upwellings that are thought to occur almost everywhere, in all the oceans.
Because these warmer layers prevent the cold water from rising from the depths, the upwelling is very slow indeed and, during this time, the colder water is heated by contact with the warmer layers above.
The ocean basins, world wide, experience this phenomenon and, therefore, unimaginable amounts of water are being moved at extraordinary speed at remarkable depths.
As yet, oceanographers still don't know the implications of these giant cataracts or how they affect the movement of krill, fish eggs, fry, migratory fish and a host of other life forms.
In the Denmark Strait the current was so severe that of thirty meters deployed, to measure the current, only ten were recovered, the rest being swept away.
In the sill region, the current was recorded at 1.4 metres a second. When one compares this to the average surface current of 0.1 to 0.5, one begins to realise that there are awesome forces at work of which we have had little or no knowledge until relatively recently.
Perhaps this might explain the barrels of toxic waste that were dumped in the Pacific and turned up on a beach in Scotland, in the UK, within a matter of less than two years,
back in the '60s. At the time this occurrence mystified one and all ... it
rather spoiled the process of keeping a low profile for the dumpers... a good
thing too. What sort of fool throws poisons into the stream at the foot of his
garden? The oceans are at the foot of everybody's garden and they need looking
after by all of us.
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