Hull of the ship Kyrenia during excavations. Hull of the Kyrenia Ship on the seabed in northern Cyprus during underwater excavations in the late 1960s. Credit: Image provided to the authors by the Kyrenia Ship Excavation team for use with this article, CC-BY 4.0
Cornell researchers have refined the estimated time frame of the sinking of the Kyrenia ship between 286 and 272 BCE by overcoming dating challenges such as removing contaminants and revising the radiocarbon calibration curve, improving to both historical understanding and broader scientific research.
Historic shipwrecks often evoke dreams of sunken riches waiting on the ocean floor to be recovered.
For Cornell researchers trying to date the famous Hellenistic-era wreck of the Kyrenia, discovered and recovered off the coast of northern Cyprus in the 1960s, the real treasure was not gold coins, but thousands of almonds found in jars 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 for the Kyrenia’s sinking between 296 and 271 BCE, with a high probability that it occurred between 286 -272 BCE.
The team’s paper was recently published in the journal 
The hull of the ship Kyrenia remains shortly after the timbers salvaged during seabed excavation were reassembled. Credit: Image provided to the authors by the Kyrenia Ship Excavation team for use with this article, CC-BY 4.0
Over the past six decades, the Kyrenia has provided archaeologists and historians with key insights into the development of ancient ship technology, construction practices, and maritime trade. To date, no fewer than three replicas of the Kyrenia have been produced and launched, and these reconstructions have provided considerable insight into ancient ships and their sailing performance. However, the chronology of the Kyrenia’s provenance and the exact date of its sinking have always been vague at best. Early efforts to date the ship were based on its recovered artifacts, such as onboard pottery and a small batch of coins, which initially led researchers to estimate that the ship was built and sunk in the late 300s BCE.
“Classical texts and discoveries at port sites have already told us that this era was important for widespread trade and maritime connections all around the Mediterranean – an early period of globalization,” Manning said. “But the discovery of the Kyrenia ship, just under 15 meters long, probably with a crew of four, made it all very immediate and real. It provided key insights into the practical aspects of the first part of a millennium of intense maritime activity in the Mediterranean, from Greece to late antiquity.
The first volume of the final publication of the Kyrenia ship project, published last year, claimed that the date of the sinking was a little later, closer to 294-290 BCE, but the main evidence – a coin poorly preserved and almost illegible – was not waterproof.
Manning’s team, which included co-authors Madeleine Wenger ’24 and Brita Lorentzen, ’06, Ph.D. ’15, sought to secure a date.
The dangers of polyethylene glycol
The biggest obstacle to accurately dating the Kyrenia has been another artifact, dating back to the 20th century: polyethylene glycol (PEG). Excavators and conservationists often applied this 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’s a petroleum product,” Manning said, “which means if you have PEG in the wood, you have this contamination with ancient fossil carbon that makes the dating radiocarbon impossible.”
Manning’s team worked with researchers at the University of Groningen in the Netherlands to develop a new method for cleaning PEG from wood. ring sequence) dates.
“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 actual (known) age,” Manning said. “Basically, we eliminated 99.9% of the PEG. »
They used this technique to remove PEG from a Kyrenia sample that Manning and his collaborators had tried, unsuccessfully, to precisely date 10 years ago. The team also dated a tiny piece of twisted wood recovered from Kyrenia in the late 1960s, but too small to be included in the reconstruction, thus avoiding PEG treatment. It then remained in a jar of water in a museum for around fifty years.
Dates showed that the most recent preserved tree rings from these woods grew in the mid-4th century BCE. Since the samples did not contain bark, the researchers could not determine the exact date that the original trees were cut down, but were able to say that the date was probably later than around 355-291 B.C. Our era.
Organic evidence
Working with Kyrenia’s original excavation team, researchers examined its various artifacts, including pottery and coins, with an emphasis on organic materials, including an astragalus (a sheep ankle bone or goat formerly used for games and divinatory rituals in several ancient cultures). and thousands of fresh green almonds found in some of the large amphorae, i.e. ceramic pots. These “short-term” samples made it possible to define the date of the ship’s last voyage.
The team applied statistical modeling combined with dendrochronology of the wood samples to achieve a much more precise level of dating than previous efforts. Modeling identified the most likely date range for the final voyage between 305-271 BCE (95.4% probability) and 286-272 BCE (68.3% probability) – several years later than current estimates.
But there was a big hiccup along the way. The new dates do not match the International Radiocarbon Calibration Curve, which is based on tree rings of known age and is used to convert radiocarbon measurements to calendar dates for the Northern Hemisphere.
Manning took a closer look at the data behind the calibration curve, which has been collected over several decades by dozens of laboratories and hundreds of scientists. He found that the period between 350 and 250 BCE had no modern radiocarbon data from accelerator mass spectrometry (AMS). Instead, the calibration curve for this period relied only on a few measurements made in the 1980s and 1990s using an older type of radiocarbon dating technology. With collaborators in the United States and the Netherlands, the team measured single-year samples of redwoods and oaks of known age to recalibrate the curve for the period 433-250 BCE. This not only helped clarify a significant peak in radiocarbon production caused by a minimum of solar activity centered around 360 BCE, but also led to significant revisions of the curve during the period around from 300 BCE – essential improvements to the dating of Kyrenia.
Manning anticipates that the new findings will not only clarify the timeline of the Kyrenia and its cargo, but also help researchers use the calibration curve for very different projects.
“This revised curve from 400 to 250 BCE is now relevant to other problems that researchers are working on, whether in Europe, China or elsewhere in the northern hemisphere,” he said. “Half of the people who cite the paper 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 wreck is really important and has a much better date.”
Reference: “A revised radiocarbon calibration curve 350–250 BCE impacts high-precision dating of the ship Kyrenia” 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