Response of Terrigenous Vegetation in North America to Climate VariationEPA Grant Number: U915883
Title: Response of Terrigenous Vegetation in North America to Climate Variation
Investigators: Gordon, Elizabeth S.
Institution: University of South Carolina at Columbia
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2001 through August 1, 2004
Project Amount: $80,027
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Oceanography , Aquatic Ecosystems , Academic Fellowships
The objective of this research project is to examine the response of North America's vegetation to variations in climate during the past 100,000 years. This research project will investigate a possible shift between C4-dominated vegetation during warm, interglacial periods, and C3-dominated vegetation during a cold, glacial period. Such a shift in vegetation may be expected based on the latitudinal distribution of grasses in North America, where C4 grasses dominate the warmer, southern regions, while C3 grasses are more abundant in the colder, northern regions. Temperature is believed to be responsible for this distribution (Teeri and Stowe, Oecologia 1976;23:1-12). A temperature-induced response of terrigenous vegetation, and therefore of agriculture, has both scientific and economic implications for future climate change, but the prediction of a future vegetation shift contains many uncertainties. The key towards understanding future vegetation changes may be provided by past variations, which are recorded in marine sediments. In particular, sediments from the Gulf of Mexico may provide a unique record of past changes in North America's terrigenous vegetation. Ancient and modern sediments will be analyzed to test the hypothesis that vegetation in the Mississippi River drainage basin changed from C4-dominated vegetation during warm, interglacial periods to C3-dominated vegetation during cool, glacial periods.
I will test this hypothesis by determining the sources and fate of terrigenous organic matter in the modern Gulf of Mexico and by examining processes that affect its deposition utilizing elemental (% OC, C/N), stable carbon isotopic (13C), and terrigenous biomarker analyses. In addition, the novel technique of compound-specific isotopic analysis will be utilized to quantify the relative contribution of C3 and C4 terrigenous vegetation in modern and ancient sediments. Surface sediments, which represent less than 10 years of deposition, and box cores, which represent 50-200 years of deposition, were collected along the inner Louisiana shelf during three sampling periods. In addition, suspended sediments were collected from both the Mississippi River and the Atchafalaya River, which transports 30 percent of the Mississippi River discharge. This comprehensive riverine and coastal coverage is necessary to constrain the composition of terrigenous organic matter that is exported from the shelf to deeper regions of the Gulf of Mexico. In addition to shelf samples, sediment samples were collected using box cores and gravity cores from nine slope stations. Finally, sediment samples from a 208.7-m piston core, which spans 100,000 years, have been donated by Dr. John Jasper. These samples will be analyzed to quantify terrigenous vegetation changes over glacial-interglacial transitions. The above sampling strategy allows for the characterization of terrigenous organic matter on yearly (surface sediments), decadal (box core sediments), centennial (gravity cores), and millennial (piston core) timescales.