Boiled or roasted? Bivalve cooking methods of early Puerto Ricans elucidated using clumped isotopes.

Cooking technique reflects a combination of cultural and technological factors; here, we attempt to constrain bivalve cooking temperatures for a pre-Columbian Puerto Rican native population using carbonate clumped isotopes. Analyses of 24 bivalve specimens (Phacoides pectinatus) from a shell midden in Cabo Rojo, Puerto Rico, suggest that samples were heated up to 200°C, indicating that roasting rather than boiling may have been the preferred cooking technique. More than half of analyzed samples exhibited a distinct change from modern uncooked shells, possibly reflecting different cooking techniques or the use of a single method wherein shells are unevenly heated, such as when placed on a heated surface. Roasting bivalves would not necessitate the use of ceramic technologies, an observation concurrent with the absence of such artifacts at this site.

Interpreting carbonate and organic carbon isotope covariance in the sedimentary record.

Many negative δ(13)C excursions in marine carbonates from the geological record are interpreted to record significant biogeochemical events in early Earth history. The assumption that no post-depositional processes can simultaneously alter carbonate and organic δ(13)C values towards more negative values is the cornerstone of this approach. However, the effects of post-depositional alteration on the relationship between carbonate and organic δ(13)C values have not been directly evaluated. Here we present paired carbonate and organic δ(13)C records that exhibit a coupled negative excursion resulting from multiple periods of meteoric alteration of the carbonate δ(13)C record, and consequent contributions of isotopically negative terrestrial organic matter to the sedimentary record. The possibility that carbonate and organic δ(13)C records can be simultaneously shifted towards lower δ(13)C values during periods of subaerial exposure may necessitate the reappraisal of some of the δ(13)C anomalies associated with noteworthy biogeochemical events throughout Earth history.