Alarming accelerated bone deterioration at famous Mesolithic peat bog

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Alarming results from a 2019 survey of well-known archaeological site Ageröd reveal drastic bone and organic matter deterioration since the site’s initial excavations in the 1940s, suggesting action is needed to preserve findings from Ageröd and similar sites, according to a study published in the journal PLOS ONE by Adam Boethius from Lund University, Sweden, and colleagues.

Archaeologists need organic remains like bone and plant matter to reconstruct ancient human cultures and environments; however, organic matter is only preserved under specific conditions, becoming rarer as sites deteriorate due to environmental change like drainage and pollution.

Boethius and colleagues here attempt to measure and analyze this phenomenon using the well-known Swedish Mesolithic peat bog site Ageröd I (8700-8200 cal BP), uncovered in the 1930s with excavations in the 1940s and 1970s, and renowned for its abundant and well-preserved quantities of bone and flint.

In 2019, the authors and colleagues excavated five test pits (five square meters total) at Ageröd, near areas containing the greatest number of remains as found in previous excavations. They then compared 61 bone, tooth, and antler fragments (as determined to the species or family level) uncovered in the test pits with 3716 bone fragments previously retrieved during the 1940s and 1970s excavations.

Osteological analyses of the bone remains from 2019 as compared with those found in the 1940s and 1970s indicate that bones at Ageröd have suffered accelerated deterioration over the last 75 years, with measured bone weathering averages going from 2.8 in the 40s (hard, heavy bones with occasional cracks) to 3.4 in the 70s (lighter bones with bigger cracks and interior exposure) to 3.7 in 2019 (light and heavily eroded bones, outer surface loss).

More worryingly, complete destruction of some bones was suggested in this latest excavation, which uncovered no smaller fur game bones or bird bones, in contrast to earlier excavations–likely because small mammals and birds have smaller, lighter bones that break down faster than heavier bones. The authors also detected oxidized pyrite in the bones from 2019, in contrast to those from the 40s and 70s (which showed only non-oxidized pyrite). This suggests that oxygen was re-introduced into the bog environment between the 1970s excavations and 2019, destabilizing the typically anoxic bog conditions and permitting pyrite to oxidize and produce sulphuric acid (which drops soil pH and damages organic matter) as a by-product.

Although the 2019 excavation was much smaller in scope than previous excavations–in part to help limit further potential destruction at the site–the careful location of the test pits suggests the decay and loss of bone remains documented here is likely indicative of issues occurring across Ageröd. The authors note that Ageröd has not been subjected to more or heavier encroachment than most other archaeological sites, raising concerns as to the state of preservation in similar sites. They note that though Ageröd still holds significance, it has already lost many of its unique preservation properties–and if future steps to protect the site are not taken, then the organic remains preserved in its peat bog for 9000 years will soon be lost forever.

Research article: Human encroachment, climate change and the loss of our archaeological organic cultural heritage: Accelerated bone deterioration at Ageröd, a revisited Scandinavian Mesolithic key-site in despair

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