Date of Award

Spring 1-26-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

First Advisor

Eve-Lyn Hinckley

Second Advisor

Kathryn Snell

Third Advisor

Timothy Seastedt

Abstract

Paleovegetation proxies inform scientists not only about what climate and ecosystems may have looked like through Earth’s history, but also give us the ability to predict what today’s global change may bring for modern ecosystems. Carbon isotope ratios of soil organic matter (SOM) and pedogenic carbonates record relative proportions of C4-derived biomass. Each soil constituent is thought to form under different soil climate conditions. Soil organic matter is thought to form under cooler and wetter conditions when climates favor the production of C3 plant biomass. Pedogenic carbonates are thought to precipitate during the warmest and driest parts of the year, when climates favor the production of C4 plants and C3 plants may exhibt water stress. In this study, I investigate if the stable carbon isotopic signatures of SOM and pedogenic carbonates record climate induced vegetation signals. I analyzed and compared the carbon isotope ratio of vegetation collected under drought conditions and wet conditions, SOM, and pedogenic carbonates from four sites that vary in vegetation community and topography in Meade Basin, Kansas. Results from this study suggest carbon isotope values of carbonates and SOM reflect carbon isotope values of vegetation from warm and dry climates and/or values that are 13C-enriched relative to warm and dry vegetation. The degree to which the carbon isotope ratio of SOM and carbonates are enriched relative to vegetation, may be controlled by the local topography. Carbon isotope ratios of SOM and carbonates are become heavier relative to warm and dry vegetation as topography increases. These findings suggest SOM and carbonates formed in lowlands may incorporate more of a vegetation derived carbon isotope ratio, while proxies formed in uplands may incorporate more 13C-enrichment affects from influences of heavy atmospheric CO2 and discrimination from decomposition.

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