A lack of oxygen in icy depths can discourage creatures that like to feast on lost wooden ships. After centuries of wear and generations of aquatic colonisers, masts and planking can disintegrate into mounds of debris and layers of seabed ooze. The research team found the ship lying intact, its hull well preserved from keel to deck, as well as its masts and some rigging. Resting on deck, leaning against the mainmast, was a small wooden boat for ferrying crew members to and from the larger ship. Various rare items were also visible, including a wooden bilge pump and a capstan, a wide cylinder used for winding up lengths of rope. The ship's anchor was also visible, and its presence helped date the wreck to the late 15th or early 16th century, Pacheco-Ruiz said. The craft was probably a merchant vessel rather than a warship, but it bore swivel guns —"a testament of the tension" at the time, according to an expedition statement.

In an interview, Pacheco-Ruiz said the wreck was 15 to 18 metres long. The Santa Maria — flagship of Columbus' expedition — is thought to have been roughly 18 metres long, with the expedition's other ships, the Niña and the Pinta, closer to 15 metres. Records indicate the Santa Maria had 52 crew members, and the other two ships each had 18. Scientists launch the ROV from the Stril Explorer. Credit:Deep Sea Productions/MMT “This ship is contemporary to the times of Christopher Columbus and Leonardo Da Vinci, yet it demonstrates a remarkable level of preservation after five hundred years at the bottom of the sea, thanks to the cold, brackish waters of the Baltic," Pacheco-Ruiz said in the university's statement. “It’s almost like it sank yesterday – masts in place and hull intact. Still on the main deck is an incredibly rare find – the tender boat, used to ferry crew to and from the ship, leaning against the main mast. It’s a truly astonishing sight.” The name and origin of the lost Baltic ship have not been identified. For now, the maritime archaeologists are calling it Okänt Skepp, Swedish for "unknown ship". Pacheco-Ruiz and his team are keeping its exact location secret, to deter scavengers and treasure hunters.

They plan to return to the site for another round of exploration, in particular to retrieve a wooden plank. Laboratory analyses can date ancient wood to within a year of its human acquisition, Pacheco-Ruiz said, which would help pinpoint when the ship was built and put to sea. The expedition is a collaboration among the Centre for Maritime Archaeology at the University of Southampton, where Pacheco-Ruiz is a fellow; the Maritime Archaeology Research Institute of Södertörn University in Sweden; Deep Sea Productions in Sweden, and MMT, a Swedish firm that performs seabed surveys, often for offshore energy companies. Pacheco-Ruiz also works for MMT as a maritime archaeologist. The March expedition was aided by doctoral students from the University of Southampton and the KTH Royal Institute of Technology in Stockholm. Those students are developing artificial intelligence to improve the maneuvering and sensing of robots in the sunless depths. University students join the expedition on board the Stril Explorer. Credit:Deep Sea Productions/MMT

The archaeological team illuminated the wreck with bright lights and took thousands of high-resolution photos; with the help of a computer, these were merged into portraits so detailed that they seem 3D. Such composites can be startlingly clear and sharp, compared to single frames, and they also can reveal the shipwreck as a whole. In contrast, even a large mosaic of close-ups typically fails to provide an overall sense of a lost vessel. In 2016, Pacheco-Ruiz used the same method to bring to light a medieval ship found at the bottom of the Black Sea. The portraits captured the hulk in remarkable detail. That expedition was also organised by the Southampton maritime archaeologists. In an interview, Johan Rönnby, director of the Maritime Archaeology Research Institute of Södertörn University, said the Baltic shipwreck was important because it opened a new window on the development of early modern sailing ships and the resulting age of global exploration. "It's something special because it's so extremely well preserved," he said. "It really looks fantastic." Over the years, marine archaeologists have learned a great deal about the age of exploration and its fleets of tall ships. "But there are gaps," Rönnby said. The Baltic discovery will help fill in some of the particulars.

"These kinds of discoveries are really, really important for our understanding of history," he said. The New York Times