La mer emporte, les os se souviennent: FTIR-ATR analysis of bioapatite preservation in skeletal remains from the 18th-century Fortress of Louisbourg to inform coastal archaeological rescue operations

For centuries, the Atlantic Ocean has been slowly eating away at the rocky shores of Cape Breton Island in Nova Scotia. As the waves reclaim the land, they are uncovering a forgotten graveyard from the 1700s, the Rochefort Point Cemetery, once part of the Fortress of Louisbourg. This is a race against time. Archaeologists must find and move the remains of the people buried there before the sea washes them away forever. But there is a problem: the ocean does not treat every grave the same way. Some bones look like they have survived intact, while others have crumbled into dust. For a long time, researchers believed they could judge the condition of these remains just by looking at them. If a bone looked solid, they assumed it was safe to study. If it looked broken, they assumed it was ruined. However, this simple visual check might be misleading the scientists, hiding the true chemical state of the bones and making it difficult to know exactly where to dig next.

To solve this puzzle, a team of researchers decided to look deeper than the surface. They turned to a technique called Fourier-Transform Infrared spectroscopy, which acts like a chemical fingerprint scanner for bone. Bones are made of two main things: a hard, mineral part that gives them strength, and a soft, protein part that gives them flexibility. Over hundreds of years, the environment can swap the minerals in the bone with minerals from the soil or water, a process that weakens the structure even if the bone still looks whole. The researchers wanted to see if the saltwater draining from the nearby ocean was speeding up this chemical breakdown, and whether looking at the bone's surface was enough to tell the difference. They focused on the femurs, the large thigh bones, of 51 individuals from the cemetery. These bones were chosen because they are dense and usually the last to disappear, giving the team the best chance to find a pattern.

The team collected tiny samples of the inner bone from each person, grinding them into a fine powder to analyze their chemical makeup. They compared these chemical results with a visual score they had given each skeleton, ranging from "excellent" to "poor." What they found was a clear and worrying pattern linked to geography. The closer a burial was to the northern edge of the cemetery, where the land meets the ocean, the more chemically damaged the bones were. The saltwater, which is rich in ions that aggressively swap places with the bone's minerals, was acting as a powerful agent of decay. This chemical damage was measurable and consistent, showing that the seawater drainage was the primary force destroying the remains, more so than the type of soil in which they were buried.

Surprisingly, the visual inspection of the bones did not match this chemical reality. The researchers found that many bones that looked perfectly fine to the naked eye were actually chemically compromised, with their internal structures already degraded by the saltwater. Conversely, some bones that looked broken were chemically sound. One specific case stood out: a young girl, aged 12 to 14, whose bones looked pristine and unbroken. Yet, the chemical analysis revealed that her bones had been heavily altered by the environment, likely due to her proximity to a hearth and the surrounding soil chemistry. This single example proved that a bone can look perfect while its molecular integrity is already gone. The study showed that relying on how a bone looks is an unreliable way to predict its condition, especially in coastal areas where saltwater is a factor.

This discovery changes how archaeologists plan their rescue missions. When time is short and the shoreline is receding, teams need to know where the best chances of finding usable remains are. The study suggests that digging further north, closer to the current water's edge, is likely to yield diminishing returns, as the saltwater has already done its work on the molecular level. The researchers propose that using this chemical scanning method offers a much clearer map of preservation than visual guesses alone. It allows teams to prioritize their efforts, focusing on areas where the bones are not just physically present, but chemically intact enough to tell the stories of the people who lived and died there. By understanding the invisible chemical battle between bone and seawater, archaeologists can ensure they rescue as many of these histories as possible before the ocean takes them back.