Fading Star: Understanding accelerated decay of organic remains at Star Carr

The early Mesolithic site of Star Carr (approximately 11 ka BP) is widely acknowledged as one of the most important wetland sites in Northern Europe. It has provided some of the most informative archaeological evidence for hunter-gatherer lifestyles in Britain at that time. However, recent observations suggest that the site is no longer providing the conditions necessary for such remarkable archaeological preservation. In 2007 and 2008, excavations at the site uncovered artefacts displaying alarming levels of diagenesis, suggesting that current conditions may be leading to the destruction of any organic material yet to be uncovered. Geochemical and hydrological investigations suggest that this is closely linked to changes occurring due to drying out of the site. However, scientific data regarding the rates and mechanisms of decay in such acidic environments are severely lacking.
The aim of this thesis is to apply an experimental approach to investigate the observed deterioration, in order to answer some key questions: Is Star Carr undergoing accelerated deterioration, and if so, how are the changing site conditions contributing to this? Ultimately, by learning more about the key factors facilitating degradation in the specific burial environments at Star Carr, strategies to slow or stop the deterioration can be recommended, both for Star Carr and other wetland archaeological sites.
A suite of appropriate analytical methods have been tested and applied to assess deterioration in both bone and wood. It has been shown that as different techniques provide complementary and sometimes contradictory information, a multi-analytical approach is needed. Using these techniques it has been shown that bone mineral rapidly dissolves in acidic solutions, buffering the acidity. As a result, collagen is left exposed and also breaks down leading to the loss of bio-archaeological information. The effects of pH on wood degradation are more subtle, but burial experiments show that drying out of the burial environment can have a severely detrimental effect on the survival of structural polymers in wood.
Analysis of material excavated from Star Carr has shown that preservation differs across the site. For bone this is closely related to the geochemical conditions. It seems likely that bone in the current state of preservation would quickly deteriorate further at the low sediment pH recorded. Due to the localised differences in geochemistry and organic preservation across the site, any mitigation strategies aimed at slowing organic decay need to carefully consider all material that may yet be buried, and their varying states of diagenesis. Rapid changes in both materials (bone and wood) following excavation have also been observed. It is recommended that post-excavation strategies be designed to slow or stop these changes.