Rings and Worms Tell the Tale of a Shipwreck Found at Ground Zero [Slide Show]
Researchers were stunned to find an 18th-century ship that had been unearthed by construction workers at the World Trade Center where the Twin Towers once stood. With great care they followed clues in the well-preserved wood to trace the craft's history to the era of the American Revolution
FINAL CREW: Evidence of more innocuous creatures was also found in the wreckage, from bones of the extinct passenger pigeon to a bright green sprig of eelgrass. Aside from some shipworm casings, all of the remains represented species endemic to the Hudson River region.
These species assemblages have now helped fill in the ship's last chapters.
It was originally assumed that the USS
Adrian—known by a different name back then, of course—had been purposely scuttled and sunk as part of the landfill that extended the shoreline of Manhattan. But these animals told a different story. More likely, the ship somehow went down off New York harbor, perhaps with the help of shipworms, and stayed put for a few years. There it accumulated a community of horseshoe crabs, sponges, oysters and snails that can only survive in salt marshes, suggests Shawn Shotzberger, an ecologist with AKRF.
Eventually, when it came time to enlarge Manhattan Island, landfill quickly swallowed up the ship and its new occupants, along with the rest of the shoreline.
"The fill must have occurred fairly rapidly, as all of the stuff was entombed and sealed off from scavengers and oxygen that would have contributed to their deterioration," Shotzberger says. "Everything we found looked like it came out of the river yesterday."
"Without the estuarine organisms that were recovered, you could paint any number of pictures about how the ship came to be there and how it was entombed in fill," he notes.
AKRF's Pappalardo highlights another unique aspect of the ship's closing chapter. "The relic was found in what formerly was the Hudson River and ultimately became the World Trade Center site," he says. "It provides a direct connection between the 18th and 21st centur[ies]—a continuum of importance of this space in trade and commerce."
AKRF, provided courtesy of LMDC
INTIMATE DETAILS: The sailors also left some more intimate items aboard the vessel. Strands of hair were found in at least 10 contexts in and around the USS
Adrian, including some black strands that were tangled up in a sea sponge.
Charlotte Pearson, a dendrochemist at Cornell University, analyzed the hair samples, including one peculiar strand that had been found embedded in tar.
"One of the first things I noticed was a human body louse," she recalls. "That was a likely indicator that it was human hair, and probably from the head."
She suggests that further analysis of the samples, which seem to represent a number of different people, might be able to pinpoint the ethnic origin of the sailors. Although it is also possible that the hair did not even belong to anyone on board. Centuries ago, at least in Pearson's native U.K., human hair was often collected from barbershops and used to hold wall plaster and other building materials together. Charlotte Pearson, Cornell University, provided courtesy of LMDC
REVOLUTIONARY FINDING: Carved wooden planks were not the only artifacts of human engineering uncovered at the World Trade Center site. Ceramics, shoes, rope fragments and ammunition were also pulled from the ship's wreckage. A brick expert at Fordham University even identified some artifacts as remains of a galley hearth.
"It looks like there was a small crew of three or four people who lived and ate, had stuff and dropped stuff," explains AKRF's Pappalardo. (They had also recovered nutshells.)
One of the most curious relics was a button bearing the number 52. A historian identified it as once belonging to a member of the British 52nd Regiment of Foot during the Revolutionary War.
Philadelphia was home to the U.S. Continental Congress before and in the beginning of the American Revolution. It was also the site of a major victory for the British army during the war. But whereas the button and weaponry found might suggest the ship's temporary use during the war, perhaps to ship supplies up and down the coast, it doesn't mean that a British soldier necessarily ever boarded the ship.
"Buttons had great value back then," Pappalardo notes. "If someone picked it up, they probably would've sewn it onto their clothes."
AKRF, provided courtesy of LMDC
SOUTHERN SLOOP: When he first saw the ancient timbers, maritime historian Norman Brouwer recalls thinking that the ship had probably been built in a small shipyard, mostly due to the lack of uniformity in the timbers and planking.
The strong agreement in ring width patterns among their samples led the Columbia researchers to the same hypothesis. The trees seemed to come from the same narrow geographic origin, which would be typical for a small ship-building operation.
"I got really excited when I discovered that the maritime historian was circling around our same conclusion," Pederson recalls. "The trends and patterns across different disciplines are fascinating—and evidence that science works."
Brouwer also initially guessed that the boat was an ancestor of the Hudson River sloop, a type of small commercial vessel built in New York during the 18th and 19th centuries. Given the tree-ring team's findings, he now acknowledges that the ship probably got its start elsewhere, perhaps initially sailing the Delaware River. He also notes that some ships built in the Philadelphia-area were likely similar in form to the Hudson River sloop.
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ARRIVING AT ANSWERS: The keel (pictured) had 144 rings. Lining these natural markings up against historical records helped the scientists trace the tree's life span: It likely sprouted in 1581 and fell in 1724 or shortly thereafter. The timber had been squared in construction, a clue that several rings were likely lost.
In the new unpublished report completed by LDEO's Tree Ring Laboratory the team dates the most recent ring among all of the samples to 1773. Whereas none of the fragments included bark—which would have been a sure sign that they counted the last ring formed before the tree was felled—this particular fragment's outer ring appeared to be in close proximity to missing bark. Further, four other samples dated back to 1769 and 1770, leading them to feel fairly confident that the ship was built in 1773, a date consistent with initial guesses based on the ship's design.
What the wood suggested about the origin of the ship, however, surprised Pederson's team. They found a consistent drop in ring widths corresponding to the late 1690s across all 19 dated oak samples. The pattern, which returned to above-average widths and then narrowed again in the 1710s was inconsistent with records from New York State's Hudson Valley. They matched very well, however, with a chronology from another major metropolitan area: Philadelphia.
Dario Martin, Lamont-Doherty, provided courtesy of LMDC
BASIC FORENSICS: After the cellophane-wrapped waterlogged wood was finally pulled from the fridge, Dario Martin-Benito of LDEO dried out one piece to see if it would decay as feared. More luck: it stayed intact. So the team proceeded to slowly dry out and sand down each of their 23 samples to uncover the detailed structures of the rings. Then they began to count and compare.
There are no fancy 3-D laser systems in the tree-ring scientists' laboratory. "The best computer is still our brain–eye system," says Pederson. "We're doing science the old-fashioned way."
Along two radii on each sample, the scientists measured growth rings down to one thousandth of a millimeter. About half of the samples contained at least 100 rings, including this slice of oak.
Dario Martin, Lamont-Doherty, provided courtesy of LMDC
TAKING FINGERPRINTS: Thanks to hungry shipworms, the ability to apply tree-ring analysis to an old wooden ship is very unusual, according to Eckelbarger. Cannons and metal parts are often all that remain of an ancient shipwreck.
Pederson and his colleagues were lucky to have recovered as much solid wood as they did from the site—such as this oak keelson, the timber that once sat atop the ship's keel. But they still had their work cut out for them. Although they may have ruled out forests across the Atlantic, there was still a wide geographic area that could have spawned the timbers.
Then good fortune struck again, as the team found a number of long reference chronologies for oak tree–rings in northeastern states that were also home to hickory. Using a technique called cross-dating, the researchers knew they could compare their samples' unique "fingerprints" of large and small rings with catalogued patterns from various species, regions and time periods. Trees typically grow wider rings during wet years and tighter rings during dry years, reflecting local climate histories. (Climate-change research is actually one of the most popular and growing uses of dendrochronology.)
Neil Pederson, Lamont-Doherty, provided courtesy of LMDC
WORMY WOOD: But a curious creature would soon reinsert some uncertainty.
Mixed in with bottles, buttons and belt buckles were telling remnants of marine life, including holes made by wood-boring clams known as shipworms—the scourge of seamen.
Shipworm expert Kevin Eckelbarger of the University of Maine's Darling Marine Center received a shipment of waterlogged hull fragments that looked more like honeycombs than wood.
He found the same shipworm species in all of the pieces he examined. Interestingly, based on its unique shell morphology, Eckelbarger determined that this particular animal was not common to New York City waters or anywhere off the U.S. Northeast's coast, for that matter. Rather, the worm species prefers warmer, high salinity waters such as the Caribbean, suggesting that the ship probably sailed well south at some point and may have endured extensive damage before it returned to New York. Whether or not the worms themselves took the ship down is not yet clear. But it wouldn't have been the first time.
"Columbus and Capt. Cook discovered that shipworms in warm water are hell on wheels," Eckelbarger says. "They are really aggressive. They make termites look like amateurs."
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HOPE IN HICKORY: As a global economic center at that time, Manhattan could have harbored ships from near and far. So identifying the USS
Adrian's origin posed a challenging task.
Most of the timbers pulled from the mud appeared to be white oak, which is very common around the world including Europe—a clue which is of little help. But the identification of another tree species among the fragments became one of the project's first big breaks.
The boat's keel was made of hickory, according to plant pathologist Robert Blanchette of the University of Minnesota. This type of wood does not grow in Europe, but is relatively common in eastern North America.
"This really clued us into the possibility of actually providing a date and origin," says Neil Pederson of LDEO. "Before that, we were concerned because it could've come from almost anywhere." Neil Pederson, Lamont-Doherty, provided courtesy of LMDC
GHOST SHIP: As excavators quickly and carefully removed the hull, stern and orlop (lowest) deck layer by layer, archaeologists labeled and photographed each piece, and even hired outside experts to scan the dig site with 3-D lasers.
"The lasers collect clouds of millions of individual points with highly detailed coordinates," says Michael Pappalardo, also with environmental consulting and planning firm, AKRF, Inc. "It sort of looks like a ghost."
Corinthian Data Capture, LLC, and their laser system were enlisted immediately after the surface of the ship was exposed, and again during the process of the relic's removal. The final result is a digital representation of each and every plank, which may later be used as a guide to reconstruct the ship's structure as it was before excavation. With additional information, archaeologists hope to someday see—at least on a computer screen—what the entire ship may have looked like when it sailed. Although it was not yet clear in what waters that may have occurred, they did already have some clues based on the form of the remnants.
The vessel is currently thought to have been between 18 and 22.5 meters long and about 4.5 meters wide. Based on the ship's width compared to its height, and the location of the sails, it was likely a type of coastal trading ship called a sloop.
Created by Corinthian Data Capture, LLC, provided courtesy of LMDC
UNDER THE WEATHER: The first challenge in solving the puzzle was simply to keep the pieces from rotting away once they were unearthed and exposed to air. After more than 200 years of being entombed in a wet, oxygen-free environment, exposure to the sun and aerobic (oxygen-using) bacteria threatened to take their toll.
Keeping wood waterlogged reduces the amount of oxygen that infiltrates within and between its cells, attracting hungry microbes. So the archaeologists used a big sun umbrella, hoses and a little help from Mother Nature—rain—to keep the wood's structure intact and to ward off the warping or cracking that would otherwise occur. And they moved fast, removing and wrapping up the remnants to maintain their moisture, and then loading them in containers to be trucked to a Maryland conservation center. There, the artifacts would be temporarily submerged in water until pieces could be shipped to experts at Lamont–Doherty Earth Observatory (LDEO) of Columbia University in Palisades, N.Y., and other institutions for analysis.
Kim Martineau, Lamont-Doherty, provided courtesy of Lower Manhattan Development Corporation (LMDC) Advertisement