The determination of late Quaternary paleoenvironments at Equus Cave, South Africa, using stable isotopes and amino acid racemization in ostrich eggshell

The stable carbon and nitrogen isotopes from organic compounds, and stable oxygen and carbon isotopes from inorganic carbonate in modern and fossil ostrich eggshell (OES) at Equus Cave, South Africa, were used to determine relative changes in C3 and C4 vegetation, rainfall, and temperature throughout the last 17 ka. Amino acid racemization and three new radiocarbon dates were used to assign ages to the individual OES fragments analyzed for stable isotopes, and to evaluate the stratigraphic integrity of the samples. The amino acid racemization and radiocarbon data indicate that most of the OES fragments are not in correct stratigraphic context, and may have been upwardly and downwardly mixed; thus, each fragment was placed in chronological sequence using radiocarbon-calibrated amino acid racemization. The stable carbon isotope data from the fossil OES do not change systematically through the last 17 ka. The ostriches primarily consumed C3 plants (between 70% and 90%), and smaller quantities of C4 plants (between 30% and 10%), indicating that a mixture of C3 and C4 plants has been in the vicinity of Equus Cave for the last 17 ka. Stable nitrogen isotope data from OES indicate that at 17 ka, mean annual precipitation (MAP) was at a minimum (190±50 mm/yr), increased steadily to modern values by 6 ka (600±150 mm/yr), and remained relatively unchanged until present. Stable oxygen isotope data coupled with nitrogen isotope data indicate that paleotemperatures were at a minimum between 14 and 17 ka, and reached their maximum in the latest Holocene. This study demonstrates the plethora of paleoenvironmental information that can be derived from analysis of three different stable isotopes (carbon, nitrogen, and oxygen) in the same sample-type (OES), and presents a new tool with wide applicability for reconstructing paleoenvironments in semi-arid and arid regions of Africa.