Lessons from Star Carr on the vulnerability of organic archaeological remains to environmental change Kirsty Higha,1, Nicky Milnerb, Ian Panterc, Beatrice Demarchib, and Kirsty E. H. Penkmana aDepartment of Chemistry, University of York, York YO10 5DD, United Kingdom; bDepartment of Archaeology, University of York, York YO1 7EP, United Kingdom; and cYork Archaeological Trust, York YO1 7BX, United Kingdom Edited by Dolores R. Piperno, Smithsonian Institution, Fairfax, VA, and approved September 13, 2016 (received for review June 7, 2016) Examples of wetland deposits can be found across the globe and recently reported loss of palynological information (10) is testa- are known for preserving organic archaeological and environmen- ment to the fragility of the paleoenvironmental remains. tal remains that are vitally important to our understanding of past This accelerated deterioration has been attributed to modifi- human–environment interactions. The Mesolithic site of Star Carr cation of the water table at Star Carr via the insertion of a series of (Yorkshire, United Kingdom) represents one of the most influen- field drains in 2000 AD. As a result, the water table now lies below tial archives of human response to the changing climate at the end the cultural layers in parts of the site (14, 15). Organic preserva- of the last glacial in Northern Europe. A hallmark of the site since tion at wetland sites is achieved primarily through the suppres- its discovery in 1948 has been the exceptional preservation of its sion of aerobic microbial activity through constant waterlogging organic remains. Disturbingly, recent excavations have suggested (16, 17). At Star Carr, in addition to this loss of waterlogging, high that the geochemistry of the site is no longer conducive to such concentrations of sulfur have been identified that are thought to remarkable survival of organic archaeological and environmental originate from pre-Holocene pyrite-rich Kimmeridge and Spee- materials. Microcosm (laboratory-based) burial experiments have tum marine clay deposits underlying the peats, which contain the been undertaken, alongside analysis of artifacts excavated from archaeological materials (14).The combination of the introduction the site, to assess the effect of these geochemical changes on the of oxygen to the sediments and these sulfur-rich deposits has led to remaining archaeological material. By applying a suite of macro- oxidation of sulfides to sulfuric acid, causing sediment pH as low scopic and molecular analyses, we demonstrate that the geochem- as 2 (14). However, robust data linking these environmental SCIENCES ical changes at Star Carr are contributing to the inexorable and changes with the striking organic deterioration witnessed within ENVIRONMENTAL rapid loss of valuable archaeological and paleoenvironmental in- 30 y at Star Carr were severely lacking (11), making an informed formation. Our findings have global implications for other wet- decision on the appropriate management of the site impossible. land sites, particularly archaeological sites preserved in situ. Focusing on the effects of site acidity on the macroscopic and archaeological remains, we undertook laboratory-based experi- organic artifacts | geochemistry | environmental change | ments to investigate the behavior of bone (18) and wood (19) in analytical chemistry | wetland archaeology high concentrations of sulfuric acid. Results indicated that acidi- fication is a major factor leading to the demineralization of bone ANTHROPOLOGY lobally, wetland and peatland deposits are an invaluable and cellulose depletion in wood (Fig. 1). Gsource of archaeological information, preserving organic However, acidity is unlikely to be the sole factor facilitating materials and macroremains that are rarely found elsewhere (1). organic diagenesis at Star Carr. Therefore, to achieve a more However, these sites are also extremely sensitive to environmental realistic representation of the burial environment, we con- – changes, particularly to changes in the water table (2 4). Un- structed three microcosms in the laboratory (20): A, containing derstanding how changing environmental conditions and geo- sand; B, containing garden compost; and C, containing peat chemical parameters affect organic preservation in archaeological collected from the Star Carr site. Saturated, fluctuating, and dry sites has become increasingly important because both human and climate-driven modifications of wetland environments Significance continue to occur worldwide (5, 6). This understanding is par- ticularly imperative because a strategy of preserving archaeo- logical sites in situ (based on the principle that avoiding Wetland deposits provide a unique repository of archaeologi- excavation protects the archaeology for the benefit of future cal and environmental information, preserving organic remains researchers) has become increasingly prevalent since the ad- rarely found elsewhere. Star Carr is an impressive example, vent of the Valetta Treaty (7). having provided unique evidence for human interactions with The wetland site of Star Carr has yielded remarkably well- the landscape at the end of the last ice age. Tragically, here we provide experimental evidence that human modifications of preserved organic remains, including 22 red deer antler head- ’ dresses thought to be used in shamanic rituals (8) and 97% of the the local environment are leading to changes in the site s Mesolithic antler barbed points found in Britain (Fig. S1)(9).The geochemistry, resulting in the rapid loss of bone and wood artifacts. Our research demands a reassessment of the as- exceptional preservation of macrofossils and pollen has also sumption that sites such as Star Carr should be preserved in allowed detailed reconstruction of the environmental context of situ for the benefit of future researchers and demonstrates the site (10); as such, Star Carr is an important archive of the that potential changes to the burial environment must be human response to the end of the last glacial in Northern Europe. considered before such a policy is pursued. Sadly, the site also represents a lesson in the immense impact that human-driven environmental change can have on our cultural Author contributions: K.H., N.M., I.P., B.D., and K.E.H.P. designed research; K.H. per- heritage: During excavations between 2006 and 2010, an alarming formed research; K.H. and K.E.H.P. analyzed data; and K.H., B.D., and K.E.H.P. wrote level of deterioration of both bone and wood was reported. the paper. Some bone samples were found demineralized (familiarly termed The authors declare no conflict of interest. “jellybones”), and much of the wood excavated was flattened and This article is a PNAS Direct Submission. extremely crumbly (Fig. 1) (11), in stark contrast to the out- 1To whom correspondence should be addressed. Email: [email protected]. standing quality of the organic remains uncovered in the initial This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. excavations in the 1940s (12) and 1980s (13). In addition, the 1073/pnas.1609222113/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1609222113 PNAS Early Edition | 1of6 Downloaded by guest on September 27, 2021 Fig. 1. Schematic of related research at Star Carr. Schematics show the basic structure of bone and wood. Observations reported following excavations at Star Carr in 2006–2010 (11) and previous laboratory-based experiments reporting changes observed in collagen and HA in bone (18) and in lignin and cellulose in wood (19) are summarized. zones were established within each microcosm, and a range of (Table S1) (18, 19). This material consisted of archaeological materials was buried in each zone for 12 mo (Fig. 2). and modern wood, archaeological and modern bone, and mod- Material was selected to enable direct comparison both with ern sheep bone that had been demineralized by treatment in material excavated from the Star Carr site and with materials hydrochloric acid [to be comparable to the jellybones excavated used in previously reported laboratory-based experiments in acid from Star Carr (11)]. After 12 mo of burial, the level of deterioration in experimental material was compared with that in archaeological bone and wood excavated from Star Carr itself, using a suite of analytical tech- Zone Sediment/ pH Redox niques: an initial visual assessment and analysis of mass loss, fol- Hydrology (mV) lowed by chiral amino acid analysis (AAR) and powder X-ray Dipwells A1 Sand/ 7.35 54 Saturated diffraction (p-XRD) for bone and Fourier transform infrared A2 Sand/ 7.4 173 spectroscopy (FTIR) and pyrolysis gas chromatography (py-GC) Fluctuang for wood. Our approach has demonstrated that under the extreme A3 Sand/ 7.26 188 geochemical conditions identified in areas of the Star Carr site, Dry both bone and wood are at critical risk of rapid and irreversible B1 Compost/ 3.58 176 deterioration; these findings have critical implications for any or- Dry zone Saturated B2 Compost/ 5.58 194 ganic materials remaining in situ at the site. Fluctuang Tubing to Fluctuang Results monitor B3 Compost/ 5.00 435 zone water level Dry Geochemical Parameters Support the Validity of Microcosm Conditions. C1 Star Carr/ 1.63 501 A geochemical survey carried out in 2009 recorded low pH in Saturated Saturated large parts of the Star Carr site, although localized variations were Tap to zone C2 Star Carr/ 1.84 559 control Fluctuang seen, appearing to correlate with the distribution of underlying water level C3 Star Carr/ 1.58 571 pyrite-rich clay lenses (14). Further geochemical analysis carried Damp out as part of this study concurred with the previous geochemical survey: Regions of high acidity (∼pH 2) existed in close proximity Fig. 2. Experimental microcosms allowing assessment of sediment type and hydrological conditions on organic decay. Three microcosms were set up in to more neutral areas (Fig. S2). 25-L fermentation buckets. A set of material was laid out in each of the 10 To enable comparison between the microcosm experiment zones as shown. The table displays the pH and redox values for each zone and the in situ burial environment, we measured pH and redox recorded on excavation.