Carbon, nitrogen, and oxygen isotopes of ostrich eggshells provide site-scale Pleistocene-Holocene paleoenvironmental records for eastern African archaeological sites

Abstract

Quantitative, well-dated, local paleoenvironmental records are necessary to 1) evaluate responses to regional to global-scale climate change at the scale of human habitats, and 2) test hypotheses regarding the effects of environmental change and human biological and cultural evolution. Ostrich eggshell (OES) fragments are common in African archaeological sequences, are amenable to 14C and 230Th/U dating, and their stable carbon (δ13C values) and nitrogen (δ15N values) isotopic compositions track local vegetation and mean annual precipitation (MAP), respectively. We review previous interpretations of the stable isotopic composition of OES, apply a novel calibration to estimate paleo-MAP (PMAP) from δ15N values, and show that oxygen isotopes (δ18O values) record evapotranspiration, which is controlled by temperature, relative humidity, and/or photosynthetic performance, if other components of the water cycle are constrained. The stable isotopic compositions of the organic fraction of OES remain unaltered to at least ∼50 ka, indicating potential to examine even older OES. We present a ∼50–4 ka record of OES δ13C, δ15N, and δ18O values from archaeological sites recording the Middle to Later Stone Age (MSA/LSA) transition at Lukenya Hill (Kenya) and Kisese II (Tanzania). Stable isotope proxies indicate contrasting but subtle changes in local paleoenvironment throughout the records at both sites, likely explained by local ecological and climatological effects that are not resolved by regional-scale paleoclimate records. These records highlight the need for additional local studies to assess the covariance of paleoenvironments and material culture. Furthermore, they indicate that the MSA/LSA transition at the two sites did not result from paleoenvironmental change.