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Dr. Heidi Sosik, seen speaking at the annual TED conference in Vancouver this week, seeks to shed light on the secrets of the ocean’s twilight zone.Bret Hartman/TED

Beneath the blue ocean waters teeming with fish lurks an otherworldly realm known as the twilight zone – the ominous name researchers use to describe depths 200 to 1,000 metres below the surface.

While some sunlight does penetrate the zone, it isn’t enough for photosynthesis, meaning life there takes on a different form.

And that life – now estimated to make up a staggering 90 per cent of the Earth’s fish biomass – could hold the key to a sustainable future, with big implications for food security and global warming, said Heidi Sosik, a senior scientist with the Woods Hole Oceanographic Institution.

“Life in the twilight zone is intertwined with Earth’s climate,” Dr. Sosik told the annual TED conference this week in Vancouver.

The Woods Hole Oceanographic Institution, located on Massachusetts’ Cape Cod, was among five recipients of money from the Audacious Project, an initiative launched at this year’s TED conference to fund projects “that have the potential to create massive, global change.”

The Audacious Project has so far raised $406-million out of $634-million needed to sustain those projects over five years.

Dr. Sosik said little is known about the twilight zone, simply because it’s very difficult to access and is exceedingly large, spanning most of the Earth. Previously, these depths weren’t thought to contain much life, but recent studies have started to show otherwise.

The current estimates of the amount of life in that zone are 10 times more than previously thought.

One inhabitant of these depths, the bristlemouth fish, is now known to be the most abundant vertebrate on the planet. “Their population is so dense that they were mistaken for the ocean floor,” said Dr. Sosik.

Bristlemouths only measure a few centimetres in length and are estimated to number in the trillions, if not thousands of trillions. Every night, they make their way with other twilight zone dwellers to more shallow waters to feed; during the day, they descend to the depths once again.

“It’s the largest animal migration on Earth,” said Dr. Sosik, speaking at the conference in Vancouver.

Importantly, during feeding, these fish absorb carbon, bringing it down to the twilight zone. Much of this carbon is then carried to the ocean floor in feces or the bodies of dead fish, keeping it out of the atmosphere.

But this natural process could be in jeopardy as depleted fish stocks have industries and countries looking deeper and deeper for protein.

“Losing species [in the twilight zone] could mean more carbon stays in atmosphere.”

Recently, some fisheries have started using large vacuums to suck up huge volumes of smaller species, such as krill. While these don’t currently reach the twilight zone, they could affect species that regularly migrate to shallower waters.

A few countries have also started giving out licences for harvesting sea life at these depths. Dr. Sosik is worried that large-scale harvesting could begin before the implications of doing so are fully understood.

“If we’re just going in blind, history suggest we will make some serious mistakes,” she said.

Furthermore, if done sustainably, Dr. Sosik says the twilight zone has great potential as a food resource.

For Dr. Sosik’s project, the funding will be used to deploy deep-sea submarines with cameras, employ sonar monitoring and collect DNA samples.

“We are ready to launch a large-scale exploration of the twilight zone,” said Dr. Sosik.

The Audacious Project aims to fund five initiatives annually with large donations coming from Virgin United, the Bill & Melinda Gates Foundation and others.

Besides the Woods Hole Oceanographic Institution, this year’s recipients include projects aiming to eliminate trachoma, help people who can’t make bail in the U.S., improve the health of black women, and launch a satellite into space to monitor methane emissions.