Divers found only a torn cable where a research station had been in the Baltic Sea.

Research Diving Center CAU

Suspect surfaces in the mysterious case of the underwater research station that vanished

Divers in the Baltic Sea remain on the hunt for an unusual sunken treasure: an 800-kilogram, €300,000 underwater scientific observatory that went missing several weeks ago. The internet has been flooded with speculative explanations—scrap metal thieves or a Russian sub, perhaps—but a few clues have surfaced to suggest a more prosaic culprit: a boat, possibly fishing illegally, somehow hooked the facility and dragged it away.

On the morning of 21 August, a Wednesday, researchers in Kiel, Germany, noticed something strange. At 8:15 a.m., data transmissions from an underwater research observatory in the Baltic Sea suddenly stopped. At first the scientists thought there might be a temporary problem with the data connection. But when divers went down 1 week later to investigate, the explanation was much worse: The observatory itself had vanished. All that was left was a frayed cable that had connected the station to land.

The observatory—a base station and an instrument platform—weighed so much that movement by natural causes such as a storm, sea animal, or strong currents have been ruled out. Speculation about wayward military submarines accidentally running into it or thieves in search of scrap metal are also probably off the mark, says Hermann Bange, a biogeochemist at the GEOMAR Helmholtz Center for Ocean Research in Kiel, who coordinates the observatory project. The station was on a seabed only 14.5 meters below the surface, too shallow for a large submarine, and “while the station was incredibly valuable to us, it was made mostly of steel that wouldn’t have much resale value.”

The most likely explanation, Bange says, is a fishing trawler that accidentally caught a much heavier target than intended or whose anchor snagged on the station. The waters around the station are a protected research area that is off-limits to all boats, but Bange says that is regularly ignored. “Fishing boats have transmitters that tell them they’ve entered the research area, but they just switch it off,” he says. Police are investigating and have asked campers at a nearby campground whether they noticed any boats in the area that morning.

A Baltic Sea observatory’s underwater sensors collected environmental data.

Research Diving Center CAU

Divers have searched in a 100-meter radius of where the station had been, Bange says. They did find tracks on the sea floor that suggest the station was dragged for some distance. “But the tracks end, and the observatory isn’t there,” Bange says. They also found a broken piece of one of the sensors. Further dives are planned this week, and GEOMAR plans to use ship-based sonar to scan for signs of the equipment. If the station still isn’t found, the nearby navy base has offered to help with its minesweepers and other scanning technologies.

The station was installed in late 2016 and was designed to complement the monthly ship-based measurements researchers have been making at Boknis Eck, a location at the entrance to the Eckernförde Bay, since 1957—one of the longest-running oceanography records anywhere in the world. The underwater station continuously recorded water temperature, salinity, currents, and levels of oxygen, methane, and carbon dioxide. It could capture data from shorter-term events such as storms or heat waves and help scientists understand the effects of those natural phenomena on the longer-term observations. Several new instruments, one to record fish populations and movements and another to measure dissolved organic material, were supposed to be installed this month.

If the station doesn’t turn up—or is severely damaged—it will take at least 6 months and more likely 1 year to replace it, Bange says. The station was insured, he says, but it will take some time to sort out the claims. “We have to see if we find any pieces.”