How almonds from more than 2,000 years ago helped researchers date this iconic shipwreck

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A lone diver first saw the ancient Kyrenia shipwreck off the north coast of Cyprus almost 60 years ago. But when archaeologists tried to determine the exact timeline when the ship came to rest on the ocean floor, they had to speculate based on the ship’s cargo.

Now a new study, published Wednesday in the journal PLOS One, may have a better time estimate of the Kyrenia’s demise — and the revelation came about thanks to recently cleaned wood samples from the ship, as well as clues from a twig, an animal bone and a supply of old almonds.

Local diver Andreas Cariolou first discovered the Kyrenia ship, one of the first large ships from the Greek Hellenistic period to be found largely intact, in 1965, and a team led by the late maritime archaeologist Michael Katzev recovered the wreck and its cargo excavated in the late 1990s. 60’s.

The researchers originally thought the ship sank around 300 BC. One text, the first part of the site’s final reports published in 2022, estimated at a range of 294 BC. to 290 BC, based on pottery and some coins found on board. But according to the latest study, no scientific dating was available to support the estimates.

The authors of a new study dated the almonds found aboard the Kyrenia ship to find a new estimated number of years for the ancient ship's final voyage.  - Excavation of Kyrenia ships

The authors of a new study dated the tonsils found aboard the Kyrenia ship to find a new estimated number of years for the ancient vessel’s last voyage. – Kyrenia Ship Excavation

Using radiocarbon dating — a method used to determine the age of organic materials, such as tree wood — and dendrochronology, the science of dating tree rings, researchers in the new study determined that the Kyrenia’s sinking occurred between 296 B.C. and 271 B.C. And they found a high probability that it happened between 286 B.C. and 272 B.C., the study authors wrote.

“We found dates that are very close to what archaeologists have recently suggested, but slightly more recent,” said lead author Sturt Manning, a professor of arts and sciences in classical archeology at Cornell University in New York.

While an updated timeline supported by scientific data is important for the famous ship, the crucial revelation lies in new techniques and a revised radiocarbon calibration that could help scientists more accurately date structures and shipwrecks from this period, Manning said.

Dating from a Hellenistic era ship

According to Manning, two major obstacles stood in the way of obtaining a highly accurate age estimate for the Kyrenia shipwreck. The first was that polyethylene glycol or PEG, a petroleum-derived compound used to preserve the ship’s wood, interfered with radiocarbon dating.

Shipwrecks are often well preserved due to the lack of oxygen at the bottom of the ocean. But once the materials are brought to the surface, they deteriorate quickly, Manning explains. Injecting polyethylene glycol into the wood prevents the wood from crumbling and turning into powder, but it becomes difficult to remove over time.

“You only have to have literally a fraction of a percent of this stuff (polyethylene glycol) on it, and the date will be wrong, often by hundreds if not thousands of years,” said Manning, who had tried to date the Kyrenia. ship 10 years ago, but failed due to PEG.

However, an international team of researchers has developed a cleaning protocol, described in an October 2021 study, that successfully removed the petroleum-based compound from wood that had been preserved relatively recently, Manning said. To confirm that the protocol would work with something as old as the Kyrenia shipwreck, Manning and his colleagues applied the technique to a piece of PEG-preserved wood that they knew was from nearly 2,000 years ago and found accurate radiocarbon ages.

Now that there was a solution to clean the wood, the researchers thought they could date the ship’s wood. But instead, they hit a second roadblock and continued to receive ages that didn’t match “any possible archaeological solution,” Manning said.

After research, he and his team determined that the International Northern Hemisphere Radiocarbon Calibration Curve, the conversion of measurements to dates based on known tree rings, was outdated for the period between about 400 BC and 250 BC.

The researchers were able to formulate their date estimate by recalibrating the curve using sequoia and oak samples of known age from this period. The revised curve was critical to finding an accurate time frame for the Kyrenia shipwreck and could further help researchers around the world with similar problems in dating ancient structures, Manning said.

A treasure of centuries-old almonds

The radiocarbon ages from the wood gave the researchers a clue as to when the ship was built, but it was a shipment of almonds that gave the study authors a guess as to when the sinking occurred, Manning said. “If you have material like almonds — or you can imagine olives or something like that that was used as a food crop — and that was on the ship when it sank, it probably had to have been there for about a year … or maybe two years older than when a ship sank.

By using the organic materials from the cargo, such as the almonds, an unidentified wood branch that was not part of the ship’s structure, and a cattle ankle bone, researchers were able to narrow down the dates and estimate a range of years for when The last voyage of the Kyrenia ship took place.

The ship's hull of the Kyrenia is seen shortly after it has been recovered from the seabed and reassembled.  - Excavation of Kyrenia shipsThe ship's hull of the Kyrenia is seen shortly after it has been recovered from the seabed and reassembled.  - Excavation of Kyrenia ships

The ship’s hull of the Kyrenia is seen shortly after it has been recovered from the seabed and reassembled. – Excavation of Kyrenia ships

“Part of the value of this story is about the process. … the (radiocarbon) dating and dendrochronology fields have grown, developed and refined over many decades,” said Mark Lawall, professor in the department of classics at the University of Manitoba in Winnipeg, in an email. “Science – whether ‘hard’ or ‘soft’ – develops over time through a lot of work ‘in the trenches’. It takes time and it takes time.” He was not involved in the new investigation.

With the small change in the estimated zinc date, it is impressive that the original dates based on archaeological evidence from ceramics and coins were off by only a few years, said Lawall, who has studied amphorae. These are ancient Greek containers used to transport wine, olive oil and other goods from the shipwreck at Kyrenia.

“The other part of the Kyrenia story is the window into past lives that are otherwise difficult to ‘see’ through the well-known ancient writers (or even lesser known),” Lawall said. “The Kyrenia crew may have been a group of more marginal traders, taking what they could, where and when they could, and hoping for a small profit at the end of the day.”

He added: “They traded with different cultures and were therefore part of a huge complex network that connected all parts of the Mediterranean. In this way we begin to understand the origins of the modern, multicultural, interconnected Mediterranean world.”

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