Oxygen may be key to life, but its absence is the key to preserving sunken artifacts.
- A pair of pants from an 1857 shipwreck sold at auction for over $100,000, sheltered from oxygen beneath the waves.
- The way in which a ship wrecks can often predict how well its contents will be preserved.
- Organic matter must be protected from oxygen and critters in order to survive a shipwreck.
Off the coast of North Carolina, the 1857 “Ship of Gold” wreck yielded a bounty of treasures, many recovered over a century later. One of the most unique items—which sold in a December 2022 auction for over $100,000—was a pair of preserved work pants, not hauled out of the ocean until 1991.
Shipwrecks and the relics hidden within can prove a fickle find. Sometimes the very ship crumbles underwater. Other times, it stands for thousands of years, only to disintegrate when it reaches dry land. Some artifacts degrade nearly immediately, and then others, such as the above-mentioned pair of pants, remain relatively unimpeded despite sitting beneath the waves for decades.
Degradation can occur due to the environmental pounding of underwater life, but also due to chemical reactions. “It depends on the environmental situation of the wreck, but most often is a combination of both,” James Sinclair, chief archaeologist for Allen Exploration, tells Popular Mechanics. His team is responsible for finding a Spanish Galleon treasure trove that was more than 350 years old.Organic materials are the fastest to degrade, especially if exposed to the open ocean, Sinclair says. “Organic materials are much more delicate than those of ceramic, glass, stone, or metallic [origin],” he says. “Organisms both large and small tend to eat away at organic material.”
Sinclair says that a white whale recently found dead in Monterey Bay National Marine Sanctuary off the coast of California will likely be completely consumed within four years. Organic material on a sunken vessel can endure the same fate.
Nathan Richards, director of Maritime Studies at East Carolina University, tells Popular Mechanics that organic materials “in oxygen-rich environments degrade fast.” But if that same material can hide from oxygen, the final results could end up quite different. “If they become buried, their preservation is altered,” he says, “and they may become very well preserved.”
“A wooden ship lost in the Baltic Sea or the Great Lakes will likely have better preservation than one lost off the coast of North Carolina,” Richards says. “There are wooden watercraft thousands of years old that have been found, and the secret to their preservation usually lies in the chemistry of the water and other geological, biological, and human factors. A wooden shipwreck buried in a beach, or in a very shallow marine environment, is likely the most at risk from human and environmental processes.”
Phil Hartmeyer, a maritime archeologist supporting NOAA Ocean Exploration, tells Popular Mechanics that “generally organic materials degrade the fastest, but archaeological site environment is the biggest determining factor of degradation rate.”
So, for organic matter to survive, being buried is the best bet, as was the case in Mr. Dement’s pants from the 1800s, found in a buried and sealed leather chest (he survived the wreck, but his gear did not).
The Differences Between Materials
The experts note that critters want a slice of this organic matter. That’s their nature. From shipworms to microbes, living creatures seek to gnaw away at food, even the timber that holds a ship together.
Richards says that iron and steel wrecks will corrode faster in salt water because the saline conditions create galvanic corrosion. Iron in the salt water also tends to “concrete,” largely a microbial process that encrusts objects. Of course, the encrusting can limit oxygen’s ability to reach the material, and, in effect, help preserve the original pieces.
“Theoretically, buried timbers in deep, dark water and encased in anaerobic sediment may be better preserved than some more modern iron or steel wrecks,” Richards says, since the cold, dark waters don’t bring on the environmental factors of living organisms and UV light deterioration.
Hartmeyer says that depending on the site, organic materials may “sometimes outlast metallic counterparts,” but often ferrous materials (which contain iron) such as steel, do last the longest.
Mix in the role of the substrate, such as a wreck settling into a sandy bottom, and you’ve got some chance for preservation. If items can reach a point of incredibly low or no oxygen levels and create anaerobic conditions to slow or stop some degradation, preservation chances increase. “If a wreck is on a rocky bottom,” Richards says, “it can’t do this.”
Sinclair says the classes of materials most likely to survive are ceramic, glass, and stone. The metal that survives the best is gold.
“There are shipwrecks that have been found off of Turkey in the Aegean that had a full load of ceramic vessels—Amphoras—that are over 3,000 years old,” he says. “At times, depending on the dispositional environment, there are even the remains of wood.”
In cold enough water, organic matter—including, unfortunately, dead human bodies—may also undergo a saponification process. In this process, fats and oils convert into a glycerol and a salt of a fatty acid, giving off a soap-like film that can last much longer.
The Black Sea, known for low oxygen levels, has some of the oldest shipwrecks in the world, sitting upright with masts intact. The state of the ship and its contents remain “highly dependent on where the vessel was lost and what the environment that it settles in is like.”
What’s the Role of Water?
A freshwater wreck will often better preserve elements of the ship due to the lack of chlorides otherwise found in sea water. “This is especially true for any iron components of a shipwreck,” Sinclair says. “Salts as well as the other chemicals in typical seawater will bind with the corrosion products of iron. They will penetrate the iron object down to a molecular level and create a new compound called ferric chloride or iron salts.”
To pull this iron out of the artifact, it must have all the chlorides removed through electrolytic reduction. This happens by setting up an electrolytic cell, with the artifact as the negative side of the cell and a sacrificial anode at the positive side. A regulated direct current is applied, and reduction happens at the surface of the object. Once enough of the chloride levels have been removed, the object can then be treated with protective coatings to prevent further deterioration.
The warmer the water, such as in the Bahamas, the more species are available to eat organic matter, meaning organic matter won’t last as long as in cold-water locations. In the case of the Titanic, the water was much too cold for the most common organic eater, the shipworm, but researchers have still found over 20 different microbes accelerating the decomposition of the ship, Sinclair says.
Steps in Preservation
Human actions, whether looting, souvenir hunting, or disruptive environmental development, can alter the wave actions, UV light, and more, impacting the preservation of a shipwreck. “Every shipwreck site will have a combination of pre-wrecking forces, wrecking processes, and post-wrecking environmental and human factors that come into play in its ultimate preservation,” Richards says.
Pulling an artifact from the sea isn’t always the wisest thing to do. Iron and metal nails can acidify and seep into the wood, which can swell with water if not eaten away. When the wood starts to dry, it can ruin it completely. Preservationists must have a batch of chemicals on hand, often polyethylene glycol, to help keep wood from turning to dust when exposed to the oxygen.
Hartmeyer says that like all archaeological disciplines, marine archaeology has matured from experience. The raising of the Alvin Clark signals a warning to the profession. Sunk in Green Bay in 1864, the ship was pulled from the water in 1969, but moving from a low-oxygen location in the depths of the water to the surface led to its full demise within 25 years. This helped with the successful preservation of the Vasa, now at its namesake Swedish museum.
“At present, the marine archeology community is largely focused on in-situ preservation, which seeks to collect archeological data and manage sites without disturbing them,” Hartmeyer says. “The commitment and cost of conservation coupled with modern site documentation methods have led archeologists and resource managers to prioritize site management and study at the site’s final resting place. Ultimately, this strategy will best preserve these important, nonrenewable places for generations to come.”
But if marine archeologists find another pair of paints, those may make it back to the surface.