The Lignin Characteristics Of Sediment Core In The Mud Area Of The Central South Yellow Sea

Terrestrial and marine materials interact with each other in the shelf marginal sea.In this area, the muddy area could record the rich information about the ancientmarine environment. The central South Yellow Sea area has been continuouslydepositing record since the Holocene. Especially, its western edge keeps a full recordof the ancient environment change information for tens of thousands of years due toits lower deposition rate so that it could provide an effective basis for inversing theancient climate and vegetation on the mainland. In this work, the concent and therelevant parameters of lignin in core N02（122o38.843’E，36o1.871’N）located in themud area of the central south Yellow Sea were analyzed. The vegetation source anddegradation pattern of the terrestrial organic carbon are indicated in that mud. Thechronology of the core N02is roughly estimated through resources. So according to it,the change of organic matter and its response to environment in thousands of yearsscales are analysed preliminary.Lignin content、 vegetation parameter and degradate parameter have beenresearched and there are main results and conclusions as follows.1. Σ8changes within0.03~0.3mg/10gds in core N02. It increases to0.3mg/10gdsas the maximum of the whole core near-46cm, and then reduces to0.06mg/10gds near-87cm. It fluctuats stably around0.1mg/10gds as the median andthe overall value is smaller below-68cm. There are two reasons for smaller datavalues of Σ8below-87cm than the top based on years of speculation. One is thatthe sediment loads from Yellow River to sea is just1/5of the content at presentbefore2~3ka. Another is that the sediment grain size is coarse2.8ka ago,which leads to adsorpting less terrigenous organic matter. Stable reducingsedimentary environment in the central south Yellow Sea is the main cause oflittle change of Σ8below-87cm when the sediment supply of terrigenous is not significantly fluctuate.2. S/V changes between0.30~3.4in core N02. A majority of them are larger than0.6but most are less than0.6within0~-20cm and-210~-230cm; all of theC/V are greater than0.05in the core. It reflects that the source of lignin in coreN02are mainly herbaceous tissue of angiosperms, but a few are found to begymnosperm. It matches the report that tissue of angiosperms are the mainvegetation types in the Yellow River basin in the mid-late Holocene. Secondly,the trends of S/V and C/V within-75~-120cm are remarkable different fromthe rest. It probably because that the climate goes through three stages ofwarm-drought-droughter in the mid-late Holocene. Moreover, the amount ofangiosperms decreases within0~-20cm. It is probably caused by thedestruction to the Yellow River prairie from Mongolian nomads. In addition, thechannel of the Yellow River is so complex, nearly recent2000years, that thespecies and quantity of terrigenous clastic plant change dramatic when inputinginto the sea. It leads to large fluctuations of S/V and C/V from0to-75cmfinally.3. There is a correlation decay between P/(V+S) and Σ8in core N02. It suggestesthat demethyl/demethoxy degradation is the most important pattern for theterrigenous organic matters. The (Ad/Al)V、P/(V+S)、(Ad/Al)Shave a relativelystable trend from top to bottom in the core N02. It indicates that the degradationof lignin occurs mainly in the soil and the rivers, rather than the sea.4. Σ8increase significantly near-100cm、-160cm、-180cm and-225cm in coreN02. According to years of speculation, they respectively correspond to3.2~3.1、4.4~4.2、5.0~4.7and5.9~5.5ka B.P. when East Asian winter monsoonincreases intensity by chance. Particularly, Σ8appears repeatedly peaking near-160cm. Is is conformit with the fact named “4.2ka” that the climate gets colderagain and again. When East Asian winter monsoon increases obviously, Yellowsea coastal current with greater intensity could carry more terrigenous organicmatter to the mud area. So for Σ8it is one kind of response to the change ofenvironment. Besides, Pon/P decreases from bottom to top in general in core N02. The most significant aspect of it is that the demarcation point of change of Pon/Pis consistent with the time when East Asian winter monsoon changes to be weak.It is speculated that Pon/P maybe, to some extent, respond to the strengthvariation of East Asian winter monsoon.