Marine carbon reservoir effects on radiocarbon ages of human bone from south coastal Peru

Sonoma State University, Rohnert Park CA

Investigators

Abstract

With National Science Foundation support, Dr. Bruce Owen will obtain radiocarbon dates on a series of human skeletons and associated archaeological materials excavated in the southern coastal region of Peru. Samples will be submitted to the University of Arizona AMS facility. Peru is of interest to many archaeologists because the region saw the rise of "pristine" civilizations, which developed independently rather than through contact with advanced peoples in other parts of the world. Although the Incan empire, described and conquered by the Spanish, is best known, it was preceded by several others. In coastal Peru the oldest sites date to more than 10,000 years in age and it is possible to trace development in time from original small hunting and gathering bands to more complex forms of social organization. Detailed research of this type however must be grounded in a secure absolute chronology and therefore considerable attention has been focussed on dating different cultural phases. Because preservation of organic material is excellent human skeletal remains are often recovered during excavation and small samples can be radiocarbon dated. What Dr. Owen and other scientists have noted is an apparent discrepancy between dates derived from human skeletal vs. other organic materials. Dates from humans who lived near the coast often appear unexpectedly old. It has been hypothesized that the reason for this lies in the substantial marine component of the foods people ate. The upwelling along the Pacific coast results in water rich in "old carbon" which is significantly different from its atmospheric counterpart. When one eats such seafood this old carbon is supposedly incorporated into the bone resulting in excessively old dates. Dr. Owen wishes to test this hypothesis by dating paired samples. In his excavations he has recovered human skeletons in association with wool clothing. If one assumes, not unreasonably, that the garments were made for the individuals, then both wool and skeletal samples should be the same age. If the bone gives consistently earlier radiocarbon dates, then the "old carbon" hypothesis will be confirmed. This approach also provides a potential technique for determining the degree of marine food in an individual's diet. The work is important because it will improve the chronological framework for prehistoric research in a crucial geographic area.