How world’s oldest seawater stays trapped in shadow zone

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How world’s oldest seawater stays trapped in shadow zone

November 13, 2017 - 20:43
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Scientists have discovered why the world's oldest seawater has remained trapped for over a thousand years.

Schematic illustration showing how the body of water is trapped.

Somewhere in the North Pacific, about two kilometres below the ocean surface, is seawater that has remained in a mysterious shadow zone for over 1,000 years.

An international team of scientists have discovered why this body of water has remained stagnant for so long. They published the results of their study in a recent issue of the Nature journal.

"Carbon-14 dating had already told us the most ancient water lied in the deep North Pacific. But until now we had struggled to understand why the very oldest waters huddle around the depth of 2km," said lead author Dr Casimir de Lavergne, from the University of New South Wales.

"What we have found is that at around 2km below the surface of the Indian and Pacific Oceans there is a 'shadow zone' with barely any vertical movement that suspends ocean water in an area for centuries,” he added.

Dubbed the oldest water in the ocean, this body of water has been trapped in an area without any vertical movement, between rising currents, arising from the shape of the ocean floor and geothermal heat sources below 2.5 kilometres and the shallower wind-driven currents closer to the surface.

This discovery holds immense potential for even more revelations to come in the future.

According to fellow author Dr Fabien Roquet from Stockholm University: “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 time scales.”

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