Nuts, bones, and wood help date a 2,000-year-old Greek shipwreck

The Kyrenia shipwreck was first discovered in 1965.
the wreckage of an ancient greek shipwreck underwater, with two divers exploring it
The Kyrenia ship hull during excavation on the seabed off northern Cyprus during underwater excavation in the late 1960s Kyrenia Ship Excavation

Gold doubloons were not the treasure that archeologists found while studying a famed Greek shipwreck. Instead, some really old almonds were the scientific bounty. Hundreds of ceramic jars of these nutritious nuts were found among the cargo of the Hellenistic-era Kyrenia shipwreck near Cyprus. 

These almonds and some newly analyzed wood samples proved to be instrumental in helping scientists from the Cornell Tree-Ring Laboratory identify the most likely timeline of the mysterious vessel’s sinking. The ship likely went down earlier than scientists once thought, between 296 to 271 BCE, with a strong probability that the ship foundered somewhere between 286 to 272 BCE. The findings are described in a study published June 26 in the journal PLOS ONE.

The shipwreck

In 1965, a town councilman diving for sponges first discovered the wreckage of the ship near the town of Kyrenia on the northern coast of Cyprus. It was the first major Greek Hellenistic-period ship ever found with a largely intact hull and was excavated from 1967 to 1969. Hundreds of ceramic vessels, some of them filled with almonds, were found inside and they were eventually reassembled offsite and scientifically studied.

“Kyrenia was one of the first times it was realized this type of rich evidence from the classical world could be found largely intact more than 2,000 years later on the seabed, if you could find it,” study co-author and Cornell University classical archaeologist Sturt Manning said in a statement. “It was a bit of a landmark moment, the idea that you actually could dive, excavate and bring up a classical-era ship and so discover this long-past world directly. Shipwrecks are unique time capsules, and you can get amazing preservation.”

[Related: X-rays are revealing new clues about a shipwreck from 1545.]

Since its discovery, archeologists and historians have used the Kyrenia shipwreck to gain insights into how millennia’s old ship technology developed alongside construction practices and maritime trade. Various reconstructions of the ship have also helped scientists determine how ancient ships sailed. However, the timeline of the ship’s origin and the exact date of its sinking has remained vague. 

Dating Kyrenia

The original efforts to date the ship were based on recovered artifacts that were not nuts, including pottery and a small batch of coins. Initially, researchers estimated that the vessel was built and sank in the later 300s BCE.

“Classical texts and finds at port sites already told us this era was significant for widespread maritime trade and connections all around the Mediterranean–an early period of globalization,” said Manning. “But the discovery of the Kyrenia ship, just under 15 meters [49.2 feet] long, likely with a crew of four, dramatically made this all very immediate and real. It yielded key insights into the practicalities of the earlier part of a millennium of intense maritime activity in the Mediterranean, from Greek through Late Antique times.”

A 2023 report on the Kyrenia ship project argued that the wrecking date was closer to 294 to 290 BCE. However, a poorly preserved coin was the primary piece of evidence, so the team sought to secure a better date using different materials.

The biggest hurdle in this quest to accurately date the ship actually came from a 20th century chemical compound–polyethylene glycol (PEG). Excavators and preservationists often applied it to waterlogged wood to keep it from decomposing after it was lifted out of the ocean. 

the timbers of a greek shipwreck
The Kyrenia Ship hull remains shortly after the reassembly of the timbers recovered from the seabed excavation. CREDIT: Kyrenia Ship Excavation.

“PEG was a standard treatment for decades. The trouble is it’s a petroleum product, which means that if you’ve got PEG in the wood, you have this contamination from ancient fossil carbon that makes radiocarbon dating impossible,” said Manning. 

The Cornell team joined forces with researchers at the University of Groningen in the Netherlands to develop a new method to clean the PEG out of the wood. They tested it on PEG-treated Roman-era samples, as this wood already had known dates based on tree-ring sequences.

[Related: Shipwreck hunters find WWII-era ship in Lake Superior.]

“We removed the PEG from the wood, we radiocarbon dated it and we showed that in each case, we got a radiocarbon age consistent with the real (known) age,” Manning said. “We basically got 99.9% of the PEG removed.”

They use that same technique on two pieces of wood from the shipwreck–one that Manning had initially tried to date 10 years ago and a small piece of Kyrenia wood that was not treated with PEG. 

The dates indicated that the most recently preserved tree-rings from these timbers grew in the middle to later 4th century BCE. The samples did not include bark, so the team hasn’t been able to determine the exact date that the original trees were felled, but estimate that it was after approximately 355 to 291 BCE.

Almonds, bones, and the radiocarbon calibration curve

The team continued to examine the various pottery and coins, with a focus on the organic materials recovered from the shipwreck. These include a sheep or goat ankle bone that was used for games and in divining rituals called an astragalus and thousands of fresh green almonds that were not treated with PEG. These more “short-lived” sample materials helped them estimate the date of the ship’s final voyage–somewhere between 305 to 271 BCE.

However, there was one scientific hiccup. The new dates that the team found did not align with the international radiocarbon calibration curve. This system is based on the known-age tree-rings and is used to convert radiocarbon measurements into estimated dates.

When Manning took a closer look at the data, he found that the period between 350 and 250 BCE had no modern accelerator mass spectrometry radiocarbon data behind it. The usable information from this period relied on only a few measurements conducted in the 1980s and 1990s, using an older type of radiocarbon-dating technology. 

To fix this, they measured known-age single-year sequoia and oak samples to re-calibrate the curve for the period 433 to 250 BCE. This helped clarify a large spike in radiocarbon production caused by a minimum of solar activity centered around 360 BCE. It also led to some important revisions to the curve around 300 BCE. 

[Related: Storm erosion brings 200-year-old shipwreck to the surface of a Florida beach.]

The team hopes that the new findings will clarify Kyrenia’s timeline and help other researchers using the calibration curve for other projects.

“This revised curve 400-250 BCE now has relevance to other problems that researchers are working on whether in Europe or China or somewhere else in the northern hemisphere,” said Manning. “Half of the people who cite the paper in the future will be citing the fact that we’ve revised the radiocarbon calibration curve in this period, and only half will be saying the Kyrenia shipwreck is really important and has a much better date.”