An octant, a 19th century instrument for navigating by the stars, lay in the sand a mile deep. A jar lay nearby.

It was an old shipwreck site all right, on the ocean bottom about 150 miles southeast of Charleston. The robot sub probed farther and found an anchor chain and a pile of empty Bahamian conch shells — either dining discards or a collection headed to wherever the ship was going.

The sub, a remotely operated vehicle, or ROV, recorded the site in late June to produce 3D images. The video feed enthralled archaeologists and others aboard the research ship Okeanos above, as well as researchers in front of video screens across the country and world.

What they saw is about all anyone knows of this mystery wreck, at least so far. The images might tell them more.

The Okeanos, a National Oceanic and Atmospheric Administration ship, has returned from a three-week exploration of the little-known deep bottom off the Southeast coast. Its archive of robot sub dive videos and photos is now available to — and owned by — the public.

Opening the archive is opening new worlds of exotic creatures, spewing methane vents and hundred of mounds of coral debris with new coral growing on top.

Maybe the biggest surprise for the researchers was simply that there is no one world down there.

"Every location was different, even the organisms growing on the individual mounds were different," said Leslie Sautter, a geology professor at the College of Charleston who was aboard the Okeanos as the marine geology leader.

Among other discoveries was a series of terraced rock flats 300 feet deep.

"Any time there was a hard rock surface, there were living organisms attached to it," she said. "Corals, sponges and urchins grew on the terraces, and brittle starfish swam the mud flats in between."

The sub was the first instrument to record a series of hundreds of mounds some 500 feet tall under the Gulf Stream. It turned out to be coral debris, literally piles of dead coral, with living coral growing along the top edge, a half-mile deep.

The sub also found methane vents, or seeps of the natural gas, in deep canyons off North Carolina. The dives weren't able to collect rock samples for College of Charleston geology professor Scott Harris, who watched from a recording lab at the college. But he couldn't be disappointed.

"The vertical rock faces and stair steps of stacked sediments viewed and sampled will hopefully provide a deeper glimpse into the ancient history of this region," he said.

The organisms the sub revealed are so otherworldly that research on similar species already has produced breakthrough medicines.

"For any kind of future work in this area, whether it's fossil fuel exploration or mineral mining, we have so much to learn before changing this sea bed," Sautter said. "We just don't know what we have out there yet. We don't know what impact we might have if we start changing it."

For now, Sautter plans to work with students next semester culling highlights from hundreds of hours of video to post online with explanatory narratives.

"I want the world to see what our dives saw," she said. 

Reach Bo Petersen Reporter at Facebook, @bopete on Twitter or 1-843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.