Stable isotopic analysis of human diet in the Marianas Archipelago, western Pacific

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 approximately 20% to approximately 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 13C-enriched (C4) plants or seaweeds. Sugar cane is an indigenous C4 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.