| Abstract: |
Proportions of marine vs. terrestrial resources in prehistoric human diets in the southern Mariana Islands (Guam, Rota, Saipan), Micronesia, have been estimated by analysis of stable isotope ratios of carbon and nitrogen in bone collagen and of carbon in apatite. The isotopic composition of marine and terrestrial food resources from the Marianas have also been determined. Experimental evidence shows that collagen carbon isotopes mainly reflect those of dietary protein sources and thus overestimate the contribution of marine animal foods. Marine protein consumption apparently ranges from ~20% to ~50% on these islands. Experiments also demonstrate the carbon isotope ratio of bone apatite carbonate accurately reflects that of the whole diet. Carbonate carbon isotope data suggest some individuals consumed significant amounts of <sup>13</sup>C-enriched (C/-4/-) plants or seaweeds. Sugar cane is an indigenous C/-4/- crop and seaweeds are eaten throughout the Pacific, but they have not been considered by archaeologists to have been prehistoric dietary staples. Apatite carbon isotope analysis has apparently identified previously unrecognized prehistoric dietary adaptations in the Mariana Islands, but this must be confirmed by archaeobotanical evidence. \bWhole vs. Partial Dietary Analyze\b Bone collagen is derived mainly from dietary proteins. Therefore, where protein and non-protein resources have different carbon isotope ratios, collagen may not accurately reflect the isotopic composition of the whole diet. This may lead to inaccurate or incomplete information avout the whole diet since vegetable subsistence sources have very little protein and low \[8,9]<sup>13</sup>C values. Bone apatite on the other hand can be used to reconstruct the whole diet. From rodent studies it has been shown that bone apatite carbonate accurately reflects that of the whole diet and does not over- or underestimate the proportions of carbon atoms from fats, carbohydrates and proteins. Isotopic analysis using apatite can resolve ambiguities in interpretation. pg 347 Humidity, temperature, light intensify and other environmental factors may also influence C/-3/- plant \[8,9]<sup>13</sup>C values in complex ways, causing small (1-3%) microhabitat and macroregional variations in foodweb carbon isotopic compostion. Carbon in marine environments is ultimately derived from dissolved bicarbonate and are intermediate between C/-3/- and C/-4/- plants. Exceptions in estuarine ecosystems.
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