LA-ICP-MS chemical analysis of archaeological otoliths as a tool for seasonality and site catchment studies

• We discuss various problems that complicate chemical analysis of otoliths.
• We focus on the use of LA-ICP-MS in otolith analysis.
• We analyze otoliths from two prehistoric sites on the Gulf Coast of North America.
• Trace elements and oxygen isotopes can provide similar results for seasonality.
• We show that trace element chemistry may be problematic for place of capture.

Analysis of the trace element chemistry of otoliths via Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) has become common in fisheries-related work, allowing biologists to trace connectivity between habitats over the life cycles of fish. For archaeological specimens, elements from the outer edges of archaeological otoliths have the potential to provide information on site seasonality complementary to oxygen isotope data; they also may inform on place of capture of fish, thus elucidating exploited ranges and/or social and economic links between settlements. Adopting this method will require careful consideration of a number of complicating factors related to metabolic processes affecting otolith production, analytical procedures peculiar to LA-ICP-MS, and diagenesis, in addition to the usual complications of species identification and assessment of sample adequacy. Here, we review such factors as they affect the utility of the method for sourcing and seasonality research with archaeological otoliths, using the results of a pilot study of specimens from two Woodland-period sites in coastal Alabama, southeastern USA, to illustrate the potential and the current limitations of the method for archaeological research.