| The Yellow Sea is one of the very broad marginal seas in western Pacific Ocean, with high productivity and organic carbon burial flux. It is also an area with strong land-ocean interaction, playing an important role in the global carbon cycling. Mud areas developed from the marginal seas preserve vast quantities of paleoenvironmental information. The analysis and determination of organic matter in sediments in the mud area of Central South Yellow Sea can provide a powerful basis for the reconstruction of paleo-vegetation and paleo-climate, which is of great geochemical significance. This thesis discussed the sources and degradation of organic matter in A01 sediment core in the Mud Area of Central South Yellow Sea, based on lignin parameters combined with other geochemical parameters. A preliminary analysis on the environmental implication has been conducted. The main results and conclusions are as following:(1)The lignin content in A01 sediment core varied in the range of 0.01～0.31 mg/10gds, with a mean value of 0.11 mg/10gds. Overall, ∑8 is stable followed by a decreasing with a subsequent stable fluctuation, and then dereases to a much bigger fluctuation. Specifically, the lignin content (∑8) is high and stable within 0～-25cm, and then decreases within-25～-75cm, with a quite stable fluctuation within-75～-150cm. A low value zone within- 175cm～-200cm has been observed, followed by a much bigger fluctuation below -200cm. As a whole, lignin content in the upper sediment core (above -75cm) is higher than that in the lower half. This is attributed to that the climate has been in a weakening winter monsoon period since 1700a B.P.. Warm and humid climate has led to a higher lignin content in the upper sediment core (above -75cm) The linear correlation coefficients of the content of S、V、C and P series monomers with the total lignin phenols (TLP) are 0.8、0.63、0.54 and 0.88. The highest coefficient of P series with TLP may be an indication that p-hydroxybenzaldehyde and p-hydroxybenzoic acid are almost entirely from the oxidation decomposition of lignin.(2) The variation range of S/V in A10 core is between 0.45 and 2.69, with a mean value of 1.21, while the range of C/V is from 0.02 to 1.57, with an average value of 0.41. These values indicate that lignin was mainly from angiosperm non-woody tissues with some contribution from woody tissues too. From the cross plot of S/V to C/V, we know that almost all terrigenous organic matter in the sediment core came from angiosperm non-woody tissues, with the exceptions at a few individual layers where contribution from woody tissues was also obvious. However, almost no gymnosperm source was found. This is in accordance with the result that the vegetation in the loess plateau region during the holocene was dominated by steppe. S/V and C/V ratioes increase with depth in the first -20cm, while S/V fluctuates stably around 1.0 between-20cm and -80cm, and it fluctuates stably with a median of 1.25 within -80～120cm. The fluctuation ranges of both S/V and C/V greatly increase within-175--225cm. Alteration of terrestrial vegetation resulted from major climate changes during the Holocene may cause large fluctuation of S/V and C/V.(3) The Pon/P ratio varied in the range of 0.03-0.24 in A01 core with an average value of 0.10. As a whole, Pon/P gradually increased with increasing of depth, indicating that vascular plant sources accounted for an increasing portion of terrigenous organic matter from modern times to the mid Holocene. Pon/P ratio fluctuated stably with a median of 0.075 between 0 cm and-110 cm, while it fluctuated around 0.09 within-110～-155cm. There was a high value zone of Pon/P ratio within-155cm～175cm, followed by a larger fluctuation between-175cm and-225cm, and then it fluctuated around 0.15.(4) (Ad/Al)v varied in the range of 0.02～1.49 in A01 core with a mean value of 0.36, while (Ad/Al)s varied in the range of 0.10～3.87 with a mean value of 1.51. These values suggest that lignin in the sediment core experienced moderate to high oxidative degradation. No obvious correlation was observed between (Ad/Al)v and (Ad/Al)s. On the whole, (Ad/Al)v and (Ad/Al)s did not increase significantly with increasing depth, indicating that lignin was not pronouncedly influenced by further oxidative degradation after being buried in the sediment. P/(V+S) varied in the range of 0.17～1.90 with an average value of 0.93 in A01 core, suggesting that lignin in the sediment core experienced a high degree of demethyl/demethoxy degradation. There is a poor correlation between (Ad/Al)v and C/V (R2=0.004), indicating that influence of oxidative degradation to C/V ratio was negligible. |
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