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In order to test this hypothesis, we exposed the right valves of modern hard clams (Mercenaria campechiensis, Gmelin 1791) cultured in the Gulf of Mexico to a variety of prehistoric cooking methods.

Our experiment comprised untreated shells (corresponding to manually opened shells and serving as controls), shells boiled in seawater (~100 °C), roasted over charcoal (174 ± 13 °C) and directly burned in charcoal (559 ± 95 °C).

otoliths (~98% aragonite, 2% calcite for Carlarius heudelotii). senilis shells were composed of 100% aragonite which is the initial mineralogy also found in modern shells-based water temperature reconstructions using the bulk shell samples result in unreasonably high palaeo-water temperature estimates (23.9 to 51.0 °C).

In contrast, the samples drilled from the hinge region of the same shells provide more realistic water temperature estimates for coastal intertidal environments (28.0 to 38.3 °C).

However, as the breakage of the burned shells occurred predominantly along the ventral margin, the thicker hinge region might still be preserved in shell midden deposits, in particular for larger shell specimens.

Error bars represent mean standard errors of the individual measurements.Based on experimental and archaeological data, we show that carbonate clumped-isotope thermometry can be used to detect and reconstruct prehistoric processing methods in skeletal aragonite from archaeological shell midden assemblages.Given the temperature-dependent re-equilibration of clumped isotopes in aragonitic carbonates, this allows specific processing, cooking or trash dispersal strategies such as boiling, roasting, or burning to be differentiated.For all treatments, exposure times ranged from 15 minutes to 6 hours. These samples comprised four catfish otoliths (Carlarius spp.) and seven bivalve shells (Senilia senilis, Linnaeus 1758). Alteration of mineralogy and geochemical proxies in modern Mercenaria campechiensis shells by simulated prehistoric cooking methods: Untreated (grey triangles and grey striped areas), boiled (blue triangles), roasted (green circles), and burned shells (orange diamonds).Afterwards, we measured the bulk clumped-isotopic composition (Δ values of mid-Holocene shell midden constituents excavated in the northern part of the Mauritanian coast (Banc d’Arguin), radiocarbon dated to 5,020–5,320 cal. We also analysed additional samples drilled from the hinge region of each bivalve shell, as well as high-resolution ontogenetic oxygen-isotope records of three exemplary shells. (a) Conversion of primary aragonite into secondary calcite with the predicted aragonite-calcite conversion based on the Arrhenius model for biogenic aragonite of Staudigel & Swart values of all treatments were significantly different from the control shells, there was no significant difference between the different cooking treatments.

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