ORCID
https://orcid.org/0000-0003-3225-8236
Date of Award
6-19-2025
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
The South American tropics encompass some of Earth's most diverse and dynamic landscapes, from tropical glaciers and arid deserts to savannahs, shrublands, and the planet’s largest and most biodiverse rainforest—spread across a vast climatic and topographic gradient. These biomes provide vital natural resources that sustain communities, bolster economies, and serve as key components of the global hydrologic and carbon cycles. Despite their environmental and socioeconomic importance, these tropical systems are highly vulnerable to contemporary and future climate change and its cascading impacts. Adding to this challenge, the scarcity and short duration of instrumental climate records from this region pose major challenges to quantifying hydroclimate and environmental responses to anthropogenic climate change. Proxy-based paleoclimate reconstructions are therefore essential for understanding pre-industrial climate variability, offering critical insights into past hydroclimate and environmental change. Yet paradoxically, high-resolution paleoclimate records from the South American tropics remain limited, especially in comparison to the northern high latitudes. This dissertation addresses that gap by presenting high-resolution local- to regional-scale reconstructions of hydroclimate and environmental change from eastern Amazonia and the Eastern Cordillera of the Colombian Andes over the past 20,000 years, using organic geochemical proxies preserved in lacustrine sediments. I first develop plant wax n-alkane δ2H and δ13C records from Lago Caranã, Brazil, to evaluate eastern Amazonian precipitation and vegetation dynamics over the past ~5600 years. I then apply the same tools to sediments from Lago de Tota, Colombia, to investigate the dynamics of the Intertropical Convergence Zone (ITCZ) and South American Summer Monsoon (SASM), and their influence on the understudied northern tropics of South America over the past ~19,300 years. Finally, I develop a method that leverages the DionexTM accelerated solvent extraction (ASE) 350 system for the selective sequential extraction and chromatographic separation of sedimentary n-alkyl lipids and polycyclic aromatic hydrocarbons (PAHs), which I apply to the Lago Caranã sediments to reconstruct late Holocene fire activity in the region. On centennial timescales, I find that expansions and contractions of the ITCZ’s seasonal range, driven by Atlantic sea surface temperature variability, may have enhanced moisture transport into eastern Amazonia throughout the late Holocene. The legacy of pre-Columbian Indigenous land use is recorded in Caranã’s n-alkane δ13C record through changes in vegetation composition and forest canopy structure, driven by both local and regional fire activity as indicated by sedimentary charcoal and PAH data. On millennial timescales, shifts in the mean position of the ITCZ, driven by variations in the Atlantic Meridional Overturning Circulation (AMOC) and intensification of austral summer insolation, increased precipitation and convection over the northern South American lowlands during the late Pleistocene and Holocene. Together, these records offer new insights into the nuanced drivers of hydroclimate and environmental change in the South American tropics, enhancing our understanding of how tropical systems respond to both natural and anthropogenic climate forcing.
Language
English (en)
Chair and Committee
Bronwen Konecky
Committee Members
Alexander Bradley; David Fike; Jeffery Catalano; Shira Maezumi
Recommended Citation
Mauceri, Alessandro Antúnez de Mayolo, "From the Amazon to the Andes: Paleoclimatic and Paleoenvironmental Changes Recorded by Sedimentary Biomarkers Since the Late Pleistocene" (2025). Arts & Sciences Theses and Dissertations. 3513.
https://openscholarship.wustl.edu/art_sci_etds/3513