Influences of summer warming and nutrient availability on Salix glauca L. growth in Greenland along an ice to sea gradient.

The combined effects of climate change and nutrient availability on Arctic vegetation growth are poorly understood. Archaeological sites in the Arctic could represent unique nutrient hotspots for studying the long-term effect of nutrient enrichment. In this study, we analysed a time-series of ring widths of Salix glauca L. collected at nine archaeological sites and in their natural surroundings along a climate gradient in the Nuuk fjord region, Southwest Greenland, stretching from the edge of the Greenlandic Ice Sheet in the east to the open sea in the west. We assessed the temperature-growth relationship for the last four decades distinguishing between soils with past anthropogenic nutrient enrichment (PANE) and without (controls). Along the East-West gradient, the inner fjord sites showed a stronger temperature signal compared to the outermost ones. Individuals growing in PANE soils had wider ring widths than individuals growing in the control soils and a stronger climate-growth relation, especially in the inner fjord sites. Thereby, the individuals growing on the archaeological sites seem to have benefited more from the climate warming in recent decades. Our results suggest that higher nutrient availability due to past human activities plays a role in Arctic vegetation growth and should be considered when assessing both the future impact of plants on archaeological sites and the general greening in landscapes with contrasting nutrient availability.

Bone biodeterioration-The effect of marine and terrestrial depositional environments on early diagenesis and bone bacterial community.

Bacteria play an important role in the degradation of bone material. However, much remains to be learnt about the structure of their communities in degrading bone, and how the depositional environment influences their diversity throughout the exposure period. We genetically profiled the bacterial community in an experimental series of pig bone fragments (femur and humeri) deposited at different well-defined environments in Denmark. The bacterial community in the bone fragments and surrounding depositional environment were studied over one year, and correlated with the bioerosion damage patterns observed microscopically in the bones. We observed that the bacterial communities within the bones were heavily influenced by the local microbial community, and that the general bone microbial diversity increases with time after exposure. We found the presence of several known collagenase producing bacterial groups, and also observed increases in the relative abundance of several of these in bones with tunneling. We anticipate that future analyses using shotgun metagenomics on this and similar datasets will be able to provide insights into mechanisms of microbiome driven bone degradation.

Fungal attack on archaeological wooden artefacts in the Arctic-implications in a changing climate.

Climate change is expected to accelerate the microbial degradation of the many extraordinary well-preserved organic archaeological deposits found in the Arctic. This could potentially lead to a major loss of wooden artefacts that are still buried within the region. Here, we carry out the first large-scale investigation of wood degradation within archaeological deposits in the Arctic. This is done based on wooden samples from 11 archaeological sites that are located along a climatic gradient in Western Greenland. Our results show that Ascomycota fungi are causing extensive soft rot decay at all sites regardless of climate and local environment, but the group is diverse and many of the species were only found once. Cadophora species known to cause soft rot in polar environments were the most abundant Ascomycota found and their occurrence in native wood samples underlines that they are present locally. Basidiomycota fungi were also present at all sites. In the majority of samples, however, these aggressive and potentially very damaging wood degraders have caused limited decay so far, probably due to unfavorable growth conditions. The presence of these wood degrading fungi suggests that archaeological wooden artefacts may become further endangered if climate change leads to more favorable growth conditions.

Predicting the loss of organic archaeological deposits at a regional scale in Greenland.

Across the Arctic, microbial degradation is actively destroying irreplaceable cultural and environmental records that have been preserved within archaeological deposits for millennia. Because it is not possible to survey the many sites in this remote part of the world, new methods are urgently needed to detect and assess the potential degradation. Here, we investigate organic deposits at seven archaeological sites located along the dominating west-east climatic gradient in West Greenland. We show that, regardless of age, depositional history and environmental conditions, all organic deposits are highly vulnerable to degradation. A state-of-the-art model that simulates the effect of future climate change on degradation indicates that 30-70% of the archaeological fraction of organic carbon (OC) could disappear within the next 80 years. This range reflects the variation within the climatic gradient and the future climate scenario applied (RCP 4.5 and RCP 8.5). All archaeological deposits are expected to experience a substantial loss, but the most rapid degradation seems to occur in the continental inland areas of the region, dominated by dry and warm summers. This suggests that organic remains from the Norse Viking Age settlers are especially under threat in the coming years.

Footprints from the past: The influence of past human activities on vegetation and soil across five archaeological sites in Greenland.

Climate change has irrevocable consequences for the otherwise well-preserved archaeological deposits in the Arctic. Vegetation changes are expected to impact archaeological sites, but currently the effects are poorly understood. In this article we investigate five archaeological sites and the surrounding natural areas along a climate gradient in Southwest Greenland in terms of vegetation types, above- and below-ground biomass, soil geochemistry and spectral properties. The investigations are based on data from site-sampling and optical remote sensing from an unmanned aerial vehicle (UAV) and satellites. Results show that the archaeological sites are dominated by graminoids with approximately two times more above- and below-ground biomass than the surrounding areas, where the vegetation is more heterogeneous. This difference is associated with a 2-6 times higher content of plant available phosphorus and water extractable nitrate and ammonium in the archaeological deposits compared to the surrounding soil. Furthermore, the vegetation at archaeological sites is less affected by the regional climate variations than the surrounding natural areas. This suggests that soil-vegetation interactions at archaeological sites are markedly different from the natural environment. Thus, the long-term vulnerability of buried archaeological remains cannot be assessed based on existing projections of Arctic vegetation change. Finally, the study demonstrates that vegetation within archaeological sites has distinct spectral properties, and there is a great potential for using satellite imagery for large scale vegetation monitoring of archaeological sites and for archaeological prospection in the Arctic.

Climate change and the loss of organic archaeological deposits in the Arctic.

The Arctic is warming twice as fast as the global average with overlooked consequences for the preservation of the rich cultural and environmental records that have been stored for millennia in archaeological deposits. In this article, we investigate the oxic degradation of different types of organic archaeological deposits located in different climatic zones in West and South Greenland. The rate of degradation is investigated based on measurements of O2 consumption, CO2 production and heat production at different temperatures and water contents. Overall, there is good consistency between the three methods. However, at one site the, O2 consumption is markedly higher than the CO2 production, highlighting the importance of combining several measures when assessing the vulnerability of organic deposits. The archaeological deposits are highly vulnerable to degradation regardless of age, depositional and environmental conditions. Degradation rates of the deposits are more sensitive to increasing temperatures than natural soils and the process is accompanied by a high microbial heat production that correlates significantly with their total carbon content. We conclude that organic archaeology in the Arctic is facing a critical challenge that requires international action.

Oxygen consumption by conserved archaeological wood.

Rates of oxygen consumption have been measured over extended time periods for 29 whole samples of conserved, archaeological wood and four samples of fresh, unconserved wood, at 50% relative humidity and room temperature. Samples from the Swedish Warship Vasa and the Danish Skuldelev Viking ships are included. Most rates were close to 1 µg O2 (g wood)(-1) day(-1) and the process persisted for several years at least. Consumption of oxygen is related to change in chemical composition, which is, in turn, related to degradation. It is thus demonstrated that despite conservation, waterlogged archaeological wood continues to degrade in a museum climate.