Earth

2,000-Year-Old Water Is Trapped in the Ocean’s ‘Shadow Zone

A mysterious, airless abyss.

The oldest water from the ocean failed to reach advanced years by accident.

Deep in the North Pacific, an immense stretch of ocean is trapped in a sort of stasis between the seafloor and strong currents, and for the ancient waters captured in this airless ‘shadow zone’, it’s practically like time stands still.

“What we have found is that at roughly 1.2 miles (2 kilometres) below the exterior of the Indian and Pacific Oceans there is certainly a ‘shadow zone’ with barely any vertical movement that suspends ocean water at a place for years and years,” says Casimir de Lavergne, oceanographer from the University of New South Wales in Australia.

“Carbon-14 dating had already told us that the most ancient water is located in the deep North Pacific Ocean. However, until today we had fought to understand why the oldest waters huddle about the depth of 2 kilometers.”

       (Fabien Roquet and Casimir de Lavergne)

The reason why, according to another analysis of deep water movements, is due to the geometry of the seafloor, which for long periods of time prevents extremely deep, dense ocean waters from moving to the top of the seafloor.

“North of 32° S, the deepness distribution of the seafloor pushes dense southern-origin waters to stream northward below a deepness of approximately 4 kilometers and also to return southward mostly at deepness larger than 1.5 kilometers (2.5 kilometers),” the team explains in its newspaper.

“We have developed a theory that explains all our observations — it’s only dependent on the shape of the ocean floor.”

Due to the seabed topography and how the trapped water nearly never reaches the sea surface, oxygen levels in the shadow zone could be quite low in contrast to waters sitting higher in the ocean — however that almost stagnant water may still support life, the team believes.

“It is perhaps not really a zone of quite flourishing life but that doesn’t mean it’s really a dead zone,” de Lavergne stated.

Even the Atlantic Ocean and the Southern Ocean usually don’t contain the exact forms of circulation traps, however, the researchers state that the Indian Ocean has an equivalent shadow zone – despite the fact that its proximity to fresh waters sourced from Antarctica mean its content is not as stagnant compared to deep reaches of the North Pacific.

Now that we understand about this submerged holding pattern, the researchers wish to explore what this signifies for ocean systems as a whole.

“When this isolated shadow zone traps millennia old seawater, in addition, it traps carbon and nutrients that have an immediate influence on the capacity of the ocean to influence climate through the years,” Holmes explained at a media release.

 

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