The deep sea glows. 

Giant, phantasmagorical creatures dwell in the dark water. 

And when marine researchers lower robots into these depths, they’re almost always spotting something rare or previously unknown to science.

“There’s so much left to explore and find in the ocean,” said George Matsumoto, a deep sea scientist who works as a senior education and research specialist at the Monterey Bay Aquarium Research Institute. “The ocean provides 98 percent of living space on Earth. We don’t know what else lives there.”

Ocean expeditions in 2021 added to a growing catalog of wild deep sea sightings and newly discovered species. Biologists emphasize humanity must better understand and protect this unique life, particularly as the prospects for mining rare metals in the deeps with tractor-like industrial equipment loom increasingly large.

“What are all the things in the ocean that see us coming and stay away?”

When you see the recent sightings below, it’s important to remember that what we glimpse in the deep sea is still inherently limited. With big, bulky exploration machines, scientists often capture footage of creatures that are too slow to get away, are too big to care, or are too small or translucent to spot on camera.

“What are all the things in the ocean that see us coming and stay away?” mused Matsumoto.

Rare footage of the giant phantom jelly

While exploring the deep sea in California’s Monterey Bay in 2021, marine scientists at the Monterey Bay Aquarium Research Institute captured rare footage of a giant phantom jelly (Stygiomedusa gigantea) roaming the deep waters.

Their video, taken by a sturdy deep sea robot, shows the jelly’s massive bell and long, drape-like arms undulating in the water. Over thousands of dives, Monterey Bay researchers have only spotted this enigmatic species nine times, though scientists first documented the phantom jelly in 1899.

“Even now, scientists still know very little about this animal,” the research institute wrote.

Often living at depths of some 3,300 to 13,100 feet beneath the surface, these creatures likely feast on small fish and plankton.

Ambitious scientists reach one of the deep seas’ most inaccessible places

The icebreaker RV Kronprins Haakon traveling through ice cover in the Arctic Ocean.
Credit: REV OCEAN

What’s more inaccessible than the deep sea? A deep sea blanketed in a thick shell of ice.

Yet during a daunting October 2021 mission called the HACON project, a group of over two dozen scientists and engineers used an underwater robot to successfully explore a cryptic ocean world some 13,000 feet beneath the surface of the ice-covered Arctic Ocean. It was the first time researchers surveyed rare volcanic vents — and the life there — in the remote Arctic.

“It opens a new frontier of exploration in the Arctic,” Eva Ramirez-Llodra, a deep sea ecologist for the Norwegian government who co-led the mission, told Mashable in October. “It’s a challenge, but it can be done.”

You can read more about the expedition here.

Amazed researchers find mammoth tusk 10,000 feet under the sea

Using a deep sea robot, marine scientists spotted an ancient mammoth tusk 10,000 feet beneath the ocean.
Credit: Darrin Schultz / MBARI

In July 2021, scientists discovered a three-foot-long tusk from an extinct Columbian mammoth some 10,000 feet beneath the ocean. Researchers collected the specimen off the California coast.

“You start to ‘expect the unexpected’ when exploring the deep sea, but I’m still stunned that we came upon the ancient tusk of a mammoth,” Steven Haddock, a marine scientist at Monterey Bay Aquarium Research Institute, said in a statement.

How did a tusk find its way to the deep sea? It’s unknown, and likely will remain unknown. But land-dwelling creatures are sometimes washed out into deeper ocean regions, perhaps during great floods.

Unusual and extremely hot deep sea world discovered

A hydrothermal vent with majestic calcite spires.
Credit: Schmidt Ocean Institute

During a fall 2021 deep sea expedition in Mexico’s Gulf of California, scientists observed wondrous vents spouting superheated fluid over two miles beneath the ocean surface. The trip, aboard the Schmidt Ocean Institute’s research vessel Falkor, used a sturdy underwater robot to find intriguing life and potentially new-to-science creatures dwelling at these dark depths. 

The hot vents in this region, called hydrothermal vents, are especially unique. Deep sea vents, discovered only relatively recently in 1977, often emit dark, chemical-rich fluid into the water. That’s why they’re called “black smokers.” But in this deep Mexican realm, the water is starkly different. It’s clear, owing to different minerals and sediments coming from inside Earth. 

As the images in Mashable’s story show, sometimes the hot fluid comes out and flows upward like a reverse waterfall, which ultimately builds majestic spires and mounds above the vents.

Unexpected life discovered in a deep, dark Antarctic world

Sponges and other creatures spotted beneath an Antarctic ice shelf.
Credit: British Antarctic Survey

Scientists drilled through over half a mile of ancient, coastal Antarctic ice in 2016. They lowered a camera and reached the seafloor, glimpsing a freezing, lightless world, hundreds of miles from any typical sources of food. 

And they found life.

Beneath the Filchner-Ronne Ice Shelf — part of an enormous ice sheet that floats over the ocean — researchers unexpectedly spotted eerie sponges on stalks and other still unidentified invertebrates clinging to a boulder. Never before had anyone observed such life isolated so far under an ice shelf, a finding the researchers reported in February in the journal Frontiers in Marine Science. 

“The ice makes it like an enormous cave,” Huw Griffiths, a marine biogeographer at the British Antarctic Survey and lead author of the research, told Mashable in February. Learn more about the expedition here.

Stunning images of deep-sea life captured by an aquatic robot

A sea snake swimming in the dark depths.
Credit: Schmidt Ocean Institute

During an 18-day expedition in the protected Ashmore Reef Marine Park (off of Australia), scientists aboard a Schmidt Ocean Institute exploration vessel dropped an underwater robot into deep, low-light depths. At some 165 to 500 feet down, it observed otherworldly corals, sea snakes, and a diversity of ocean creatures. The Schmidt Ocean Institute, a non-profit ocean research organization, called the trip the “Australian Mesophotic Coral Expedition.” (Mesophotic means dark zones with low light.) 

“Having studied corals from the Great Barrier Reef to Antarctica, it is easy to think I have seen it all,” the expedition’s lead scientist, Karen Miller of the Australian Institute of Marine Science, wrote in a blog post. “But experiences like the Australian Mesophotic Coral Expedition are humbling and make me realize just how much more there is still to learn about our oceans.” 

The expedition captured never-before-seen footage of the Ashmore Reef’s seabed, and also collected 500 specimens to study, the institute said. 

You can see more expedition images in this Mashable story.

A rare whalefish sighting

In California’s Monterey Bay, marine scientists filmed footage of a rarely seen whalefish at some 6,600 feet beneath the surface.

They have no eyes, and must use other senses (like picking up vibrations passing through the water) to perceive their surroundings. 

“Whalefishes have rarely been seen alive in the deep and many questions remain regarding these remarkable fish,” the Monterey Bay Aquarium Research Institute wrote.

Staggeringly bad: Scientists uncovered a massive underwater waste dump off Los Angeles

A waste barrel dumped off the Los Angeles coast.
Credit: DAVID VALENTINE, UC SANTA BARBARA / AUV SENTRY

Some deep sea discoveries are ghastly.

A dumpsite off the Los Angeles coast, littered with barrels of waste, had been mostly hidden from the public eye for over half a century. In 2021, marine scientists revealed the extent of the sprawling field of submerged waste, some of it likely toxic. 

They detected around 27,000 barrels, some at 3,000 feet deep. 

“It was staggering to us,” Eric Terrill, chief scientist of the expedition and an oceanographer at Scripps Institution of Oceanography, told Mashable. 

Read about the unsettling discovery, and what comes next, on Mashable.

Big, glowing sharks

Scientists observed bioluminescence in three deep sea shark species near New Zealand.

The kitefin shark (D. licha), is now the largest known glowing vertebrate, at some six feet long.  

“Bioluminescence has often been seen as a spectacular yet uncommon event at sea but considering the vastness of the deep sea and the occurrence of luminous organisms in this zone, it is now more and more obvious that producing light at depth must play an important role structuring the biggest ecosystem on our planet,” the researchers wrote.  

You can view the images in the online research.

The deep sea will continue to stoke amazement, even among scientists who know it best. 

In the coming years, decades, and beyond stay tuned for more discoveries, including invaluable medicines found in the deep sea. “Systematic searches for new drugs have shown that marine invertebrates produce more antibiotic, anti-cancer, and anti-inflammatory substances than any group of terrestrial organisms,” notes the National Oceanic and Atmospheric Administration.

Although the deep sea is largely inaccessible for most of us, you can still bring sounds from 3,000 feet beneath the ocean into your room. A deep sea microphone in Monterey Bay records all sorts of creatures, and sometimes the low-pitched vocalizations of whales. 

“That’s pretty amazing,” said the Monterey Bay Aquarium Research Institute’s Matsumoto.