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The ability to measure the radiocarbon content of compounds isolated from complex mixtures has begun to revolutionize our understanding of carbon transformations on earth. Because samples are often small, each new compound isolation method must be tested for background carbon contamination (C ex). Here, we present a new method for compound-specific radiocarbon analysis (CSRA) of higher plant-derived lignin phenols. To test for C ex, we compared the Δ14C values of unprocessed lignin phenol containing standard materials (woods, leaves, natural vanillin, and synthetic vanillin) with those of lignin phenols liberated by CuO oxidation and purified by two-dimensional high-pressure liquid chromatography (HPLC) coupled to mass spectrometry (MS) and UV detection. We assessed Cex associated with (1) microwave assisted CuO oxidation of bulk samples to lignin phenol monomers, (2) HPLC purification, and (3) accelerator mass spectrometry (AMS) sample preparation. The Δ14C of purified compounds (corrected for Cex) agreed, within error, with those of bulk materials for samples that were >10 μg C. This method will allow routine analysis of the Δ14C of lignin phenols isolated from terrestrial, aquatic, and marine settings, revealing the time scale for the processing of one of the single largest components of active organic carbon reservoirs on earth. © 2010 American Chemical Society.

This study demonstrates that intracrystalline organic matter in coral skeletons is well preserved over century timescales. The extent of preservation of organic matter in coral skeletons was investigated by measuring total organic carbon (TOC), total hydrolyzable amino acid (THAA), chloropigment, and lipid concentrations in 0-300 year old annual growth bands from Montastraea annularis (Florida Keys) and Porites lutea (Red Sea). Organic matter intrinsic to the calcium carbonate mineral (intracrystalline) was analyzed separately from total skeletal organic matter. The Red Sea coral had less TOC (0.02-0.04 wt%) than the Florida Keys coral (0.04-0.11 wt%), but a higher percent of intracrystalline organic matter in all annual bands measured. Carbon in the form of THAA, most likely from mineral-precipitating proteins, contributed 30-45% of the TOC in both corals. Carbon in lipids represented about 3% of the TOC in the coral skeletons. Chlorophyll-a and b were present in annual bands where endolithic algae were present, but these compounds were minor contributors to TOC. The distribution of specific organic compounds showed that organic matter was well preserved throughout the time period sampled in both the total and intracrystalline pools. Variations in THAA were not correlated with TOC over time, suggesting that organic matter that is involved in biomineralization, like amino acids, may be deposited in response to different environmental factors than are other components of skeletal organic matter. Differences in the quantity and composition of organic matter between the two corals investigated here were assessed using principal components analysis and suggest that location, species and skeletal structure may all influence organic matter content and possibly the degree of physical protection of organic matter by the coral skeleton. Further, our study suggests that intracrystalline organic matter may be better protected from diagenesis than non-intracrystalline organic matter and may therefore be a more reliable source of organic matter for paleoceanographic studies than total skeletal organic matter. © 2003 Elsevier Science Ltd.