Assessing the viability of diatom, starch granule, and phytolith analyses to trace seaweeds in archaeology

Seaweeds are a notoriously challenging non-human community to trace archaeologically due to their ephemeral nature and the relatively novel archaeological science methods required for identification in the archaeological record. This article presents an assessment of micro-remains present across twenty-one modern seaweed species (i.e., macroalgae) collected in southern (Rogaland) and northern (Nordland) Norway as part of the Seaweeds in Archaeology to Promote Sustainable Consumption (SEARCH) project. Through modern observations, we discuss the potential and limitations of epiphytic diatoms, starch granules, phytoliths and other marine micro-remains (e.g., cyanobacteria filaments) to be used as diagnostic evidence for tracing seaweed archaeologically. These observations are complemented by experimental archaeology cooking trials and ashed seaweed samples to mimic the effects of seaweed processing techniques on micro-remains and assess their deposition, preservation, and identification potential in the archaeological record. Reflecting upon the modern, experimental, and ashed samples we suggest that epiphytic diatoms are the most reliable and likely to preserve proxy for tracing seaweed (although with some caveats) along with multicellular structures (e.g., cortex tissues), while starch granules and phytoliths were not conclusively observed as reliable or broadly diagnostic.