| Lignin is a group of phenolic polymers which is abundant in the woody tissues ofvascular land plants, and is essentially absent from all other living organisms. It istransported to the ocean exclusively via fluvial rather than aerial input, and isreasonably stable while buried in marine sediment. Except for a few seaweeds, thereis essentially no occurrence in any other marine organisms. Especially with abundantparameters, it is served as one of the most important molecular fossils for tracingTerrestrial Organic Matters (TOMs) in marine environment. The fate of terrestrialorganic carbon (TOC) in the ocean is the key to understanding the global carboncycling. A key requirement for defining the marine fate of TOMs is to distinguish andquantify this often-small component in complex water and sedimentary matrix. Ligninhas been widely accepted and applied since1970s as a tracer of TOMs in marineenvironment. In recent years, lignin has found its extensive applications in thereconstruction of the input, transport, sedimentation and burial of TOMs in differentenvironmental settings, as well as the inversion of paleoenvironmental andpaleoclimate changes, etc.In this work, a modification of the conventional alkaline CuO oxidation combinedwith GC for the determination of lignin in marine sediments is reported. To constrainthe origin and contribution of TOC to the total organic carbon buried in the YellowSea and the East China Sea shelves, lignin phenols in marine sediments were analyzedtogether with other organic geochemical parameters. Research on the verticaldistribution and characteristics of lignin in the sediment cores could reconstructsedimentary record of TOC and understand the factors controlling the origin, transportand burial of TOC. Comparative studies on the lignin characteristics of the sedimentcores in different mud areas would show the different response of terrestrial vegetation on the change of climate and supply scientific evidence to predict the effectof climate change in the future. The major achievements of the study are as following:(1) A modification of the conventional alkaline cupric oxide (CuO) oxidationmethod has been established, in which a solid phase extraction (SPE) and a novelon-column derivatization were employed for better efficiency and reproducibility. Inspiking blanks, recoveries with SPE for the LOPs were between77.84%and99.57%with relative standard deviations (RSDs) ranged from0.57%to8.04%(n=3), whilethose with traditional liquid-liquid extraction (LLE) were from44.52%to86.16%with RSDs from0.53%to13.14%(n=3). Moreover, the reproducibility was greatlyimproved with SPE, with less solvent consumption and shorter processing time. Theaverage efficiency of on-column derivatization for LOPs was100.8%±0.68%, whichis significantly higher than those of in-vial or in-syringe derivatization, with still lessconsumption of derivatizing reagents. Lignin in the surface sediments sampled fromthe south of Yangtze River estuary, China was determined with the establishedmethod. Recoveries of72.66to85.99%with standard deviation less than0.01mg/10gdry weight were obtained except for p-hydroxybenzaldehyde.(2) The lignin content in the surface sediment of the Yellow Sea is higher than thatin the south of Yantze River, which is decreasing with the distance off shore. Theorganic matter derived from vascular plants in the south of Yangtze River is less thanthat in the Yellow Sea. But nonwoody angiosperm plants dominate the terrestrialorganic matter in all samples of the research area. According to the lignin parameters,the organic matter in the south of Yangtze River is originated from the suspendedparticulate matter in the Yangtze River. LPVI as a single proxy of entire characteristicof terrestrial vegetation shows that TOM is mainly from angiosperm in the north of35°N, and in the south of35°N angiosperm is the main source in the east of123°Ewhile gymnosperm in the west of123°E. The lignin in the research area is moredegraded by demethyl/demethoxy and less degraded by oxidation.(3)In a sediment core ZY2in the mud area of the middle South Yellow Sea, thesource of organic matter is nonwoody angiosperm and is stable, with the exception ofgymnosperm in a short period. The terrestrial organic matter is highly degraded. Lignin molecular fossil combined with AMS14C dating was used to establish thetemporal series of the East Asian Winter Monsoon (EAWM). It is indicated thatEAWM was highly fluctuated during6000～4200a B.P., weakened during4200～3500a B.P., strengthened in4084a B.P., relatively stable during3500～1800a B.P.,and weakened-strengthened-weakened during1800～100a B.P. As a good indicator ofenvironmental change, lignin record well inflects the climate change.(4)In another sediment core in the mud area southwest off Cheju Island, theevolution of EAWM with two distinct periods was identified according to lignindetermination. Both the content and characteristic parameters of lignin are stableabove80cm, which correspond to the relatively stable period of EAWM. In thisperiod, origin and contribution of terrestrial organic matter were reatively stable.Nonwoody angiosperm dominated the terrestrial organic matter with high degradationlevel. However, both the source plant type and contribution of terrestrial organicmatter were fluctuant below80cm, which we believe was resulted from thefluctuation of EAWM. Questioningly, the degradation level of organic matter in thesediment was decreased along with the burial time.(5)The content of lignin in the sediment core near the Yangtze River is similar tothat in the mud area along Fujian and Zhejiang coastline. Terrestrial organic matter inboth sediment cores was derived from nonwoody angiosperm, with a little fraction ofwoody tissues mixed in specific periods. Gymnosperm doesn’t contribute to theorganic matter in these areas. The terrestrial organic matter was weakly degraded,primarily oxidatively, without obvious change with the burial time. |
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