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Century-scale High-resolution Temporal Sequences Of Total Organic Carbon In Fine-grained Sediments In The Yellow-east China Seas And Their Mechanism Of Carbon Burial

Posted on:2018-01-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q ZhuFull Text:PDF
GTID:1310330536476270Subject:Marine biology
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Continental shelf,as a bridge between continent and ocean,occupies only 7-10% of the global sea area,but contributes 10-30% of the global marine primary production,30-50% of total inorganic carbon(TIC),and more than 80% of the sedimentary total organic carbon(TOC)buried in the shelf.Shelf is an important carbon sink of terrestrial and marine TOC.Therefore,the variation of sedimentary TOC in shelf seas becomes one hot topic of oceanological sciences,and will provide necessary evidence for studying global carbon cycle and climate change.The author systematically measured diverse chemical parameters,including TOC and total nitrogen(TN)and their stable isotope ratios(?13C and ?15N)in sediment cores H43,H44 and DH5-1,and performed the high-throughput sequencing in sediment core SS2 in the fine-grained sediment district in the central South Yellow Sea(SYS)and the Min-Zhe fine-grained sediment belt.Combining with the data of 210 Pb dating and BC contents,the author established a new method to correct sedimentary TOC,and centurial high-resolution temporal sequences of initial sedimentary TOC.In comparison with the data of marine particulate organic carbon(POC)and nutrients as well as the temporal sequences of precipitation in the reaches of great rivers,the newlyobtained temporal sequences were accordingly interpreted,revealing the burial mechanisms of century-scale sedimentary TOC,and discussing the impacts on marine sedimentary TOC from natural processes and human activities.Based on the analysis of microbial communities in core SS2,the effects on carbon burial from the mineralization of TOC in early diagenesis are also discussed.The main results of this thesis are described as below:(1)The method to quantitatively measure the contents of TOC in sediment cores was evidently improved,i.e.,disposable microporous-controlled ceramic crucibles with the ability to remove carbonates in sediments were used to avoid the loss of TOC,and remarkably enhance the accuracy of the TOC measurements and data stability.The model for correcting TOC in early diagenesis was modified,i.e.,TOC was divided into labile TOC and refractory TOC(i.e.,BC),then the labile TOC was corrected for early diagenesis to obtain the initial sedimentary TOC.The improved methods mentioned above provide a technical support to obtain the centuray-scale high-resolution TOC temporal sequences.(2)The centurial high-resolution TOC temporal sequences were established and interpreted in the South Yellow Sea,implying that the terrestrial TOC(TOCter)contents were gradually decreased,which resulted from the decrease of the Yellow River discharge;while the marine TOC(TOCmar)contents were gradually increased due to the nutrient increase into the sea enhanced by heavy storms and/or strong human activities.(3)The centurial high-resolution TOC temporal sequence was established for the Min-Zhe mud sediment belt.This sequence possesses the strenuous TOC variations with two V-shaped valleys.The great TOC variations may be a signal of the impoundment of the Gezhou and Three Gorges dams,which seriously affected the ecological system of the East Chia Sea(ECS).(4)The centurial high-resolution temporal sequences of TN contents and their ?15Nsed ratios were built in the intersectional region between the Yellow Sea Warm Current(YSWC)and Yellow Sea Coastal Current(YSCC)in the SYS.It is found that the nitrogen cycling in core H43 was mainly controlled by the YSWC;while that in core H44 was mainly affected by the YSCC.There is the correlation between the temporal sequences and Pacific Decadal Oscillation(PDO)index to certain extent;and the enhancement of the nitrogen input induced by human activities may evidently affect the nitrogen cycle in the shelf sea.(5)The microbial diversity in a sediment core was systematically analyzed for the Min-Zhe mud sediment belt in the inner ECS,suggesting that there was a evident vertical zonation in microbial communities,i.e.,aerobic,facultative and anaerobic communities occurred in the shallow,intermediate and deep parts,respectively.This zoning is basically consistent with those of redox and chemical components in pore water in the organic carbon mineralization.
Keywords/Search Tags:Total organic carbon(TOC), Organic carbon correction, Temporal sequences, Mineralization, Microbial diversity
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