A spatially-explicit record of prehistoric maize agriculture from compound-specific carbon isotope analysis

Authors: Zachary Taylor*, Berry College, Chad Lane, University of North Carolina-Wilmington, Sally P Horn, University of Tennessee
Topics: Paleoenvironmental Change, Biogeography, Physical Geography
Keywords: paleoenvironments, lake sediments, Costa Rica, stable carbon isotopes, maize
Session Type: Poster
Day: 4/5/2019
Start / End Time: 3:05 PM / 4:45 PM
Room: Lincoln 2, Marriott, Exhibition Level
Presentation File: No File Uploaded

Stable carbon isotope ratios measured from lake sediments are an effective proxy for land-use change and climate reconstruction. Compound-specific techniques offer significant advantages over bulk analysis because they are able to distinguish between autochthonous and allochthonous carbon. Long-chain, odd numbered alkanes are established biomarkers for terrestrial vegetation. δ13C analysis of these alkanes is a useful indicator of changes between C3 and C4 photosynthetic pathway as well as water stress on vegetation. In this paper, we present a δ13Calkane record from five cores recovered from Laguna Zoncho, Costa Rica. Previous work using pollen, bulk stable carbon isotope, and geochemical analysis has shown the lake and its basin were heavily impacted by prehistoric maize agriculture. In general, the δ13Calkane data show a similar pattern as the δ13Cbulk record with a prominent agricultural signal. Both records show less negative isotope values, due to increased C4 inputs, from the start of the record around 3,000 BP until agricultural abandonment at 675 BP. The close agreement of these records indicates that terrestrial carbon dominating the signal at Zoncho. Additionally, the same pattern holds true for mid-length C23–C25 alkanes, typically associated with emergent vegetation, and C27–C33, which are biomarkers for terrestrial vegetation. This pattern is similar throughout the lake basin, with relatively consistent signals across all five cores.

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