Abstract
Stable carbon and nitrogen isotopes are often used to make inferences of past environments and social patterns. We analyze δ 13C and δ 15N values in contemporary kukui (Aleurites moluccanus) endocarp to examine the effects of site environment. Results from across environmental transects on Hawai‘i Island show strong patterns for both stable isotopes. For δ 13C a robust linear relationship with elevation is exhibited, strengthened by the inclusion of rainfall. This relationship breaks down at a minimum threshold of annual rainfall, possible relating to physiological responses to drought. For δ 15N, the only significant relationship observed pertains to substrate age. The endocarp from kukui is one of the most readily identified plant remains in the Pacific archaeological records and is often targeted for radiocarbon dating. We discuss the potential implications of our results regarding ancient climate, inferred diets, and habitat composition.
Highlights
Stable isotopes, those of carbon and nitrogen, are often used to make inferences on past environments and social patterns, from inferring diets of ancient humans [1, 2] and animals [3, 4], to examining changing weather and climate [5,6,7] to reconstructing past habitat composition [8] and processes [9]
Carbon and nitrogen stable isotope analysis is a well-established technique for reconstructing diet from human or animal tissue, made possible by consistent and predictable isotopic fractionation throughout food webs. δ 13C values can be used to determine the proportions of C3 and C4 foods consumed, as differential 13C fractionation during photosynthesis generates distinct values for C3 versus C4 plants, which are passed reliably up the food chain [10]
Results showed high levels of 13C discrimination, with δ 13C values ranging from -20.8 to -29.5 ‰. (S1 Table)
Summary
Those of carbon and nitrogen, are often used to make inferences on past environments and social patterns, from inferring diets of ancient humans [1, 2] and animals [3, 4], to examining changing weather and climate [5,6,7] to reconstructing past habitat composition [8] and processes [9]. Carbon and nitrogen stable isotope analysis is a well-established technique for reconstructing diet from human or animal tissue, made possible by consistent and predictable isotopic fractionation throughout food webs. Nitrogen stable isotope ratios can be used to estimate trophic position within a food web, as δ 15N values undergo a ~3–5‰ stepwise enrichment between trophic levels [11,12,13]. Within such studies, less attention is paid to the local. Identifying and controlling for such variation is critical to accurate archaeological interpretations of food webs and diet
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