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Late Quaternary Climate Variability and Terrestrial Carbon Cycling in Tropical South America

Kyrstin Fornace, Ph.D., 2016
Valier Galy, Co-Advisor
Konrad Hughen, Co-Advisor

In this thesis, I use stable isotope and radiocarbon analysis of vascular plant biomarkers in lacustrine and marine sediment cores to explore late Quaternary climate variability and connections between past climate change and terrestrial carbon cycling in tropical South America. I investigate temporal and spatial trends in South American Summer Monsoon precipitation by reconstructing hydrologic variability over the past 50,000 years in the Lake Titicaca drainage basin and the Pantanal wetlands. Diverging hydrologic trends at these sites suggest altered monsoon circulation patterns under glacial conditions, while summer insolation appears to be an important control of precipitation at both sites during the Holocene. I next assess the relationship between climate change and the age structure of terrestrial biospheric carbon exported from two tropical catchments over the past 20,000 years. Radiocarbon dating of leaf waxes in Cariaco Basin and Lake Titicaca sediment records indicates that sedimentary waxes are composed of a fresh component transported to sediments within decades of production by vegetation and an old component with average age on the order of millennia at time of deposition. Overall, my results show that past hydrologic variability had a significant impact on the mobilization and export of different pools of terrestrial biospheric carbon.