Kyrenia ship hull during excavations. Kyrenia ship hull on the seabed off the coast of Northern Cyprus during underwater excavations in the late 1960s. Credit: Image provided to authors by the Kyrenia Ship Excavation team for use with this article, CC-BY 4.0
Cornell researchers have refined the estimated sinking period of the Kyrenia shipwreck to between 286 and 272 BCE by overcoming dating challenges such as removing contaminants and revising the radiocarbon calibration curve, improving both historical understanding and broader scientific research.
Historic shipwrecks often conjure up dreams of sunken riches waiting at the bottom of the ocean to be recovered.
For the Cornell researchers trying to date the famous Hellenistic-era Kyrenia shipwreck, discovered and recovered off the northern coast of Cyprus in the 1960s, the real treasure was not gold coins but thousands of almonds found in pots were found among the cargo.
The almonds, combined with recently cleaned wood samples and the team’s expertise in modeling and radiocarbon dating, led the Cornell Tree-Ring Laboratory to identify the most likely timeline of the Kyrenia’s sinking as sometime between 296 and 271 B.C. .CE, with a high probability that it took place between 286 and 272 BCE.
The team’s paper was recently published in the journal PLOS ONE. The lead author is Sturt Manning, Distinguished Professor of Arts and Sciences in Classical Archeology in the College of Arts and Sciences.
The Kyrenia has a legendary legacy: the first large ship from the Greek Hellenistic period, found in 1965, with a largely intact hull. From 1967 to 1969 it was excavated along with its cargo, including hundreds of ceramic vessels, then reassembled elsewhere and scientifically studied.
“Kyrenia was one of the first times it was realized that this kind of rich evidence from the classical world could be found largely intact on the seabed more than 2,000 years later, if you could find it,” says Sturt Manning. “It was a bit of a milestone, the idea that you could actually dive, excavate and bring up a ship from the classical era and directly explore this long-gone world. Shipwrecks are unique time capsules and you can get great preservation from them.”
The ship’s hull of Kyrenia remains shortly after the reassembly of the wood recovered during the excavation of the seabed. Credit: Image provided to authors by the Kyrenia Ship Excavation team for use with this article, CC-BY 4.0
Over the past sixty years, Kyrenia has provided archaeologists and historians with important insights into the development of ancient ship technology, construction practices and maritime trade. To date, no fewer than three Kyrenia replicas have been produced and launched, and these reconstructions have provided significant information about ancient ships and their sailing performance. However, the timeline of the Kyrenia’s origins and the exact date of its sinking have always been vague at best. Initial efforts to date the ship were based on the recovered artifacts, such as the pottery on board and a small batch of coins, which initially led researchers to estimate that the ship was built and sunk in the late 300s BC.
“Classical texts and finds at port sites already told us that this era was important for widespread maritime trade and connections around the Mediterranean – an early period of globalization,” Manning said. “But the discovery of the Kyrenia ship, just under 50 feet long, probably with a crew of four, dramatically made this all very immediate and real. It provided important insights into the practical aspects of the first part of a millennium of intense maritime activity in the Mediterranean, from Greek times to late ancient times.”
The first part of the definitive publication of the Kyrenia ship project, published last year, argued that the scrapping date was somewhat later, closer to 294–290 BC, but the key piece of evidence – a poorly preserved, almost illegible coin – was not watertight.
Manning’s team, including co-authors Madeleine Wenger ’24 and Brita Lorentzen, ’06, Ph.D. ’15, was trying to secure a date.
The dangers of polyethylene glycol
The biggest hurdle to accurately dating the Kyrenia is another 20th century artifact: polyethylene glycol (PEG). Excavators and conservationists often applied the petroleum-based compound to waterlogged wood to prevent it from decomposing after being removed from the oxygen-free environment of the ocean.
“PEG was a standard treatment for decades. The problem is that it is a petroleum product,” Manning said, “which means if you have PEG in the wood, you have a contamination of ancient fossil carbon that makes radiocarbon dating impossible.”
Manning’s team worked with researchers from the University of Groningen in the Netherlands to develop a new method to remove PEG from wood, and they demonstrated it on PEG-treated Roman-era samples from Colchester, England, which have already dendrochronological (tree) calling order) data.
“We removed the PEG from the wood, we radiocarbon dated it and we showed that in each case we got a radiocarbon age that was consistent with the true (known) age,” Manning said. “We basically removed 99.9% of the PEG.”
They used that technique to remove PEG from a Kyrenia sample that Manning and collaborators had tried a decade ago but could not date accurately. The team also now dated a small, twisted piece of wood recovered from the Kyrenia in the late 1960s, but which was too small to be included in the reconstruction, thus avoiding PEG treatment. It then stood in a jar of water in a museum for more than fifty years.
The dates showed that the most recent preserved tree rings of these trees grew in the mid-4th century BCE. Because the samples contained no bark, the researchers could not determine the exact date the original trees were felled, but they could say the date was probably after about 355-291 B.C. used to be.
Organic evidence
Working with the original Kyrenia excavation team, researchers examined the various artefacts, including pottery and coins, with an emphasis on organic materials, including an astragalus (an ankle bone of a sheep or goat once used for games and divination rituals in several ancient cultures ). and thousands of fresh green almonds found in some of the large amphorae, that is, ceramic pots. These “ephemeral” sample materials helped determine the date of the ship’s last voyage.
The team applied combined statistical models with the dendrochronology of the wood samples to obtain a level of dating that was much more accurate than previous attempts. The modeling has shown that the most likely dates for the last voyage are between 305-271 BC. (95.4% probability) and 286-272 BC. (68.3% probability) are – several years more recent than current estimates.
But there was one big problem along the way. The new dates did not match the international radiocarbon calibration curve, which is based on tree rings of known age and used to convert radiocarbon measurements into calendar dates for the Northern Hemisphere.
Manning took a closer look at the data behind the calibration curve, collected over decades by dozens of labs and hundreds of scientists. He found that the period between 350 and 250 BCE was devoid of modern radiocarbon data from accelerator mass spectrometry (AMS). Instead, the calibration curve during this period was based on just a few measurements taken in the 1980s and 1990s using an older type of radiocarbon dating technology. Together with collaborators in the US and the Netherlands, the team measured samples of annual sequoia and oak trees of known age to determine the curve for the period 433-250 BC. to recalibrate. This not only helped elucidate a major spike in radiocarbon production caused by a minimum of solar activity around 360 BCE, but also led to important revisions of the curve in the period around 300 BCE. – improvements that were crucial for the dating of the Kyrenia.
Manning expects the new findings will not only clarify the timeline of the Kyrenia and its payload, but also help researchers use the calibration curve for very different projects.
“This revised curve from 400-250 B.C. is now relevant to other problems that researchers are working on, whether in Europe or in China or elsewhere in the Northern Hemisphere,” he said. “Half of the people who quote the article in the future will cite the fact that we revised the radiocarbon calibration curve during this period, and only half will say that the Kyrenia shipwreck is really important and has a much better date. ”
Reference: “A revised radiocarbon calibration curve 350–250 BCE affects the high-precision dating of the Kyrenia ship” by Sturt W. Manning, Brita Lorentzen, Martin Bridge, Michael W. Dee, John Southon and Madeleine Wenger, June 26, 2024, PLOS ONE.
DOI: 10.1371/journal.pone.0302645