δ13C and δ15N variations in terrestrial and marine foodwebs of Beagle Channel in the Holocene. Implications for human paleodietary reconstructions

In this article we evaluate the isotopic variability in δ13C and δ15N values of diets among maritime hunter-gatherers of the Beagle Channel (Southern Argentina). A system with two end members –marine and terrestrial resources– is not enough to describe populations with diversified subsistence strategies. Moreover, these marine hunter-gatherers are characterized as highly mobile groups whose foraging ranges comprised not only nearshore areas, but also offshore spaces. As a first step to distinguish the diversity of prey choices during the Late Holocene, and to improve the accuracy of paleodietary interpretations, we conducted stable isotope analyses on zooarchaeological collections and modern samples of shellfish and plants. We observed that δ13C and δ15N values of aquatic animals are more clustered than expected in comparison to modern ecological parameters. Terrestrial prey, such as the guanaco, showed considerable isotopic dispersion in both carbon and nitrogen. While zooarchaeological studies have identified foraging activities in offshore spaces, stable isotope analyses should use different criteria to characterize long-term dietary patterns. With this local isotopic frame of reference, we re-examined δ13Ccollagen and δ15Ncollagen measurements of seven adult individuals from the Beagle Channel. Most individuals had marine diets complemented with resources more depleted in 13C and 15N than aquatic prey. While previous interpretations stated that the complementary staple was terrestrial protein, we suggest consumption of shellfish as another possibility. Finally, plants should be reconsidered as a source depleted both in 13C and 15N for mixing models, when typically underestimated in paleodiets from subpolar environments.