Testing the limits of lacustrine faecal lipid biomarkers as tools to document human and herbivore presence in Alaskan and Eastern Beringian landscapes

Sedimentary archives of faecal steroid biomarkers offer insights into human and animal presence and environmental impacts in past landscapes. However, interpretations of faecal stanol records, used to suggest early human arrivals in regions such as northern Alaska, are constrained by limited modern reference data and uncertainties associated with mixed stanol sources in wetlands. Here, we assess the sensitivity and validity of lacustrine faecal steroid reconstructions of human and animal presence within the landscape by combining analyses of modern faecal samples and a sediment archive from Chisholm Lake in central Alaska, where relative historical and archaeological population changes are well documented. Results from modern faecal samples reveal clear dietary signatures: herbivore steroid distributions are discrete from omnivores/carnivores, and multivariate analyses reveal differences between ruminant species and even herds, highlighting the influence of diet on steroid distributions. Comparisons of sedimentary 5β-stanols reconstructions with independent records of human activity show that large-magnitude population changes are reliably resolved, whereas small changes often are not, likely due to the signal-to-noise characteristics of the depositional systems. Bile acid detection was intermittent in this sedimentary archive, which limits characterisation of faecal sources and requires further taphonomic examination in lake sediments. Our findings caution against solely relying on 5β-stanol ratios to identify human faecal input in sedimentary archives because of overlapping distributions between humans and other omnivores/carnivores (e.g., Canidae, such as wolves and dogs) and mixed sources of sterol production and transformation in wetlands. Robust faecal steroid reconstructions of population change require multivariate analytical approaches that are integrated with archaeological evidence and expanded modern reference faecal steroid datasets.