Alteration of Otolith Aragonite: Effects of Prehistoric Cooking Methods on Otolith Chemistry

Geochemical analyses of fish otoliths from archaeological sites are a valuable source of paleoclimate data. A common assumption in such research is that the otolith chemistry is unaltered from the time of capture until excavation. Although post-depositional diagenesis will vary between sites according to local burial conditions, the effects of common pre-depositional treatment such as cooking or trash disposal can be evaluated experimentally. Six Atlantic croaker (Micropogonius undulatus) and six gafftopsail catfish (Bagre marinus) were treated using five different methods to simulate cooking and trash disposal. The left sagittal otolith was removed as an experimental control prior to cooking or burning each fish. After cooking or burning, the remaining otolith was removed and each otolith pair was tested to measure changes in crystallography, carbon and oxygen isotope content, and elemental chemistry. Recrystallization and changes in isotope chemistry only occurred in burned otoliths. In contrast, elemental composition was altered during each treatment method. These experiments validate the use of carbon and oxygen isotope analyses of unburned otoliths in paleoclimate research, but suggest caution in the interpretation of elemental data.