A SYNTHESIS OF CARBON ISOTOPE RATIOS OF SOIL PROFILES IN THE MAYA LOWLANDS

There exists a growing corpus of carbon isotope ratios from soil profiles of the tropical forests of the Maya Lowlands. This research first started with investigations on the agricultural terraces at the Maya site of Caracol to understand if they provided evidence for C₄ plants, i.e. maize, production in antiquity. This paper will review the techniques, general findings, and potential pitfalls of the carbon isotope records from multiple sites. First, we consider sample preparation such as the use of the humin fraction versus acid fumigated soil organic matter. Second, we consider a typology of soil environments including sinkholes, floodplains, wetland fields, agricultural terraces, and slope toposequences. Third, we present a range of AMS-dated carbon isotopic profiles from sequences that have evidence of past C₄ species. These include profiles from areas with pollen or phytolith evidence for maize and grasses dated to ancient Maya times or have contemporary evidence of modern pastures or crops with topical C₄ grasses like sugarcane. Then we compare these with carbon isotopic profiles that appear to have no evidence of past C₄ species influences on the soil organic matter such as from old growth forests. Finally, we present an assessment of the strengths and weaknesses of carbon isotopes as proxies in soils archaeological work in these tropical lowlands.