Compound specific radiocarbon and stable isotopes of lignin biomarkers
Culp, Randolph Alan
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The source and preservation of organic matter in rivers, estuaries and the coastal ocean are important factors for understanding the global carbon budget. The stable carbon isotope ratios of organic matter, including compound specific ratios, have been used rigorously to assess the inputs, origins and preservation mechanisms of organic carbon in the marine environment. 14More recently, radiocarbon (C) signals carried by organic matter have been used to assess residence time and distinguish organic inputs to the marine environment based on the age of sediments and the individual compounds found therein. Recent advances in chromatographic separation of individual compounds from complex mixtures, and subsequent isotopic analysis, have enhanced our understanding of organic carbon distribution in the marine environment. The coupling of these techniques allows determination of the stable isotopic composition of specific biomarkers like lignin phenols. Due to their source specificity to terrestrial vascular plant matter and their refractory nature, lignin phenols represent a very important fraction of the organic matter found in the marine environment. My overall research objective is to examine the relative contributions of river delivered terrestrial organic carbon from both C3 and C4 sources in the Georgia coastal marine environment by determining molecular isotopic signatures and their response to variations in flow rate, degradation and mineral interaction. Specifically I plan to 1. Demonstrate the feasibility of isolating individual lignin phenols from terrestrial organic materials and measure 14their respective C age using accelerator mass spectrometry (AMS). 2. Determine the seasonal 1413variation in isotopic abundance of C and /C in sediment, as affected by factors such as soil erosion, biochemical degradation, mineral association, and transport pathway. 3. Determine the relative inputs of organic matter from C3 or C4 plants and soil erosion or plant litter, by 1413measurement of C and /C abundance of specific lignin phenols respectively, to enable a 14distinction to be made between terrestrial plants and marine plankton. 4. Compare the C age of lignin phenols with the concentration of the acid and aldehyde lignin phenols to test the applicability of the acid to aldehyde ratio as an indicator of degradation status. 5. Compare lignin 14phenol C content in various mineral grain size fractions to understand the transport pathways of various terrestrial organic matters into the ocean.