Wrinkles are still visible on the face of “Tolund Man”, even though he died more than 2200 years ago. The Mossy Wetlands in Denmark that mummify her body are ideal for the conservation of organic materials, giving archaeologists an extraordinary window into our discursive past. But recent excavations at a similar marshland in Sweden show that these perfect conditions are fragile, and when broken, carcasses, bones, and other biological remains have been preserved for centuries. . The discovery reveals a long-standing theory of archeology – the need to avoid excavation and to leave artifacts in the ground for long-term preservation – needs to be recast, at least for some wetland sites.
Wetland archaeologist Benjamin Gière at University College Cork says that encostal evidence has long suggested that wetlands such as peat bogs are leading to declining excavation conditions. For example, bone caries have been documented at Star Carr, an archaeological site in northern England. But it is difficult to know how widespread the pattern is – and how fast the decay is happening.
Adam Beet, a peat bog in the south of Sweden that captures bones, antlers and other artifacts from Mesolithic cultures that flourished 8000 years ago, is a good place to measure the speed of decay in a peat dog, says Adam Boethius Archaeologist at Lund University. Boethius and his colleagues excavated anew in comparison to the bones in 2019, which were extracted from the marshes in the 1940s and 1970s and were stored at the Lund University Historical Museum. He evaluated the weathering of each bone, from well-preserved ones – which were shiny and crack-free – to smoothed bones with worn out bones.
The bones were so damaged by the 2019 excavation that their scoring system broke. Some had lost more than half a centimeter of their outer layer. Other parts of the site where they hope to find no bones are found in all of them, suggesting that they had completely disintegrated. The best preserved bones from the 2019 excavations were in almost the same condition as the worst bones of the 1970s, they write here today one more.
He found that the decline was already underway in the 1970s. The excavation of bones was more frequent than these excavations in the 1940s. What’s more, the same pattern appeared with the 2019 bones: the best preserved 1970s bones were in the same condition as the worst preserved 1940 bones.
Researchers say the culprit is oxygen. The organic material trapped under the moss surface of intact peat bogs is starved of oxygen, making an environment very hostile to fungi and bacteria that would normally break plants or bones. But the excavation brings oxygen, which reacts with buried iron sulfide to produce sulfuric acid. Another factor is farming activity, which has gradually drained the wetlands, damaging the protective surface and allowing oxygen. It is very likely that groundwater has become more acidic throughout the region, Boethius says. This means that bones soaked in deep, wet layers will rapidly perish. The increasing frequency of extreme weather events induced by climate change — including both droughts and floods — can also contribute to the problem, he says.
The study, says Guyer, is “adventurous,” and shows “catastrophic damage to irreparable biological archaeological remains” in Wetland sites across Europe. Archaeologist Martin Bell of Reading University says how important it is for researchers to better understand conservation and decay, also points out that the default strategy of preserving remains on the ground raises questions.
“If you can’t conserve it in the ground, you have to dig it,” Gere says. With poor understanding and monitoring of the conditions of Wetland sites, leaving treasure in the ground at sites such as Agord is not an option for Boethius. “We need to dig now,” he says. “If we wait 10 or 20 years, everything will end.”