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Back in 2017, scientists thought they may have found the answer to the mysterious 'shadow zone' in the centre of the Pacific Ocean.

This trough, roughly two kilometres below the surface, reportedly contains water which has not moved for almost '2,000' years, since the fall of the Roman Empire.

Water being water, it usually moves around due to currents, but this area is almost completely stagnant.

The zone lies in the North Pacific, almost dead centre. It is the oldest and deepest of the shadow zones that exist on Earth, in other oceans such as the Indian and Atlantic. Unaffected by ocean currents, the stagnant zone's location and reason for its existence in that place, has baffled scientists.

In a paper published in the journal Nature in November 2017, Dr Casimir de Lavergne seeks to explain why the zone has gone undisturbed for so long.

The paper Abyssal ocean overturning shaped by sea floor distribution explains that lack of vertical movement between ocean currents had meant the water has stayed put. Fellow author Dr Fabien Roquet wrote:

When this isolated shadow zone traps millennia old ocean water it also traps nutrients and carbon which have a direct impact on the capacity of the ocean to modify climate over centennial timescales...

The stagnation also means there is less oxygenation going on in the shadow zone, which lessens the amount of life in there. Lavergne adds:

It’s not a zone of very flourishing life but that doesn’t mean it’s a dead zone.

The paper's abstract suggests the geometry of the ocean basins of the Pacific, Indian, and Atlantic oceans is the cause for the shadow zones to form.

According to News Au, the researchers hope this paper will help scientists better understand how oceans absorb heat, a question crucial to climate scientists.

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