Hakai Magazine

Coastal science and societies

sea floor
The deep seafloor is full of mysteries. Photo by Martin Habluetzel/Alamy Stock Photo

Pulling Up a Piece of Hades’s Home

Expeditions to the hadal seafloor are turning up a trove of surprising discoveries.

Authored by

by Asher Mullard

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A sleep-deprived and bleary-eyed Ashley Rowden peers anxiously over the side of the RV Tangaroa as it floats some 800 kilometers northeast of New Zealand. As soon as the ship hauls its deep-sea probe out of the water and Rowden sees that his precious payload is safely back on deck, his fatigue gives way to excitement. The team had just pulled up a sample of sediment from the depths of the ocean—9,994 meters below sea level—setting a new record for mud collection.

“There were a lot of high fives, and we’re not really into high fives in New Zealand,” says Rowden, a scientist at New Zealand’s National Institute of Water and Atmospheric Research and co-leader of the expedition.

At 6,000 to 11,000 meters below sea level, the gaping trenches that cut through the ocean floor are one of the last remaining wildernesses. These seascapes are called hadal zones, a tribute to Hades, the Greek god of the underworld. Although researchers sent sampling hardware down to these cold crushing depths during a golden age of ocean exploration in the 1960s, they’ve made few return visits since. That is at last starting to change.

In part, biologists keen to understand how life survives at the limits are drawn to the hadal trenches, hunting for bacteria and animals that have evolved to survive under extreme pressure in the pitch dark and bitter cold.

The swift approach of deep-sea mining may be driving renewed scientific interest in these regions as well, Rowden says. The world’s first commercial mining extraction project could start as soon as this year, and the recent discovery of a bonanza of rare earth elements at nearly 6,000 meters below sea level suggests that hadal seascapes might one day offer up marine mother lodes. The hadal zone also provides a unique lens through which to study how disturbing the deep sea influences marine life, informing models of how shallower seabed mining operations could affect surrounding ecosystems.

With this uptick in interest, Rowden and his peers are having to relearn how to explore the nethermost nooks of the ocean.

The tried-and-true setup that he used on the RV Tangaroa is the cheapest way down. In the oceanographic equivalent of a six-hour session of the arcade favorite claw crane, Rowden and his colleagues used a greasy, half-inch-thick wire that is two kilometers longer than Mount Everest is tall to lower a heavy metal corer to the seafloor. “It’s a lot of trial and error,” says Rowden.

But simple setups can yield surprising results in rarely visited regions of the world. The newly collected samples show that the deepest areas of the Kermadec Trench are each lined with unique sedimentary deposits.

His colleagues are analyzing the samples to see how they differ in form, density, and structure, as well as microbiological and faunal makeup. These findings will help scientists build models of how carbon is cycled through the deep sea, and unveil new species of microbes. They could also provide insight into how fishing, mining, and earthquakes can affect marine ecosystems, Rowden says.

The Tangaroa is one of just a few ships equipped with enough wire to collect sediment from the hadal seafloor, and Rowden trusts that this technique will keep returning surprises from the deep. But a different deep-sea exploration technology stands to uncover even more of the ocean’s secrets.

Deep-sea landers are self-propelled submersibles that free-fall to the seafloor, and then dump their ballasts to float back to the surface. Landers bridge the gap between the simplicity of wires on winches and the sophistication of multimillion-dollar remotely operated vehicles. By loading landers with baited traps and cameras, researchers can collect otherwise inaccessible data. In 2012, using a lander, Rowden and some colleagues caught footlong shrimp-like amphipods at 7,000 meters. Last year, one of his colleagues filmed snailfish in the Mariana Trench at a depth of over 8,000 meters, making it the deepest fish ever recorded.

Rowden hopes that once the cost of landers falls far enough, researchers can drop them en masse and leave them on the hadal floor to collect data for years at a time. “The lander is where the technology is going to go in the future,” he says.

As technology improves, the field will enter a more mature phase. For now, oceanographers are limited to exploring and observing the hadal sea. But soon they may also be able to conduct experiments at depth. Scientists are not there yet, Rowden says, “but it’s not far off.”