Sedimentary ancient DNA analysis from the Iron Age courtyard and cooking pit site of Rodskjaer in Troms, Northern Norway

Courtyard sites, which are Iron Age structures unique to Norway, are often associated with cooking pit fields suggesting feasting practices, but little is known about the main purpose of these sites. To address this, a framework for sedimentary ancient DNA (sedaDNA) metabarcoding sampling was undertaken at the site of Rodskjaer, northern Norway. Of the 63 sediment samples from cooking pits, fire pits, a hearth, a fireplace, the natural shell-sand and topsoil, 52 successfully detected plant and animal sedaDNA. The plant diversity was high with 41-100 taxa. SedaDNA identified archaeologically significant taxa that were not detected by other methods, including Avena (oats), Quercus (oak), Equus (horse), and Salmo salar (salmon). Additionally, from inter-sample comparison, and with reference to worm sedaDNA we identified the archaeological contexts that were affected by partial bioturbation and root penetration that restricted interpretation of spatial or temporal differences in use of these features. This pioneering study shows the importance of taking many samples from modern and natural sediments as well as using multi-proxy analysis when conducting sedaDNA metabarcoding studies at open-air archaeological sites. If these factors are taken into consideration, sedaDNA from cooking pits can be a valuable resource for investigating uses of courtyard and cooking pit field sites.