Plant delta 15N: A new archaeological tool

This empirical study was undertaken to test the unlikely postulate that past human activity has left an imprint on the stable nitrogen isotopic ratio of the plants currently growing on archaeological sites. In each of three summers, plants were taken from a variety of defined features at Norse and Thule sites in southwest Greenland. The data obtained clearly establish the effect of past human activity on the 15N of modern plants. Despite the sites being in widely separated regions and of varying ages, the plants from each had si gnificantly higher 15N values than those growing on the surrounding natural terrain. The unusual values were directly correlated to defined activity areas and the isotopic effect was measured at the metre scale. The magnitudes of the values observed within each context were consistent with the expected delta 15N of the various nitrogen sources deposited at these locales in the past, indicating the very strong conservation of the isotopic composition of the anthropogenically introduced nitrogen. These observations show that plant delta 15N can be used as a new, non-invasive tool to identify and delineate ancient human activity, and to some extent to characterize that activity based on the magnitude of the signature. Whereas more study is needed to fully realize both the potential and the limitations of the tool, the data obtained provide a basic framework for future application. The usefulness of the tool is already demonstrated by the important information obtained for Norse farming practices in Greenland. Continued study of t he phenomenon will likely provide many applications in archaeology and perhaps will be of interest to other disciplines.