Assessment And Reconstruction Of Environmental Conditions In The East China Sea And Eastern Equatorial Atlantic:Application Of Organic Molecular Markers

Organic molecular markers are of vital importance to understand the impacts of anthropogenic organic compounds in the marine ecosystem and mechanisms that govern paleoceanography variability.Organic molecular markers were applied to study two different regions(East China Sea;ECS and eastern equatorial Atlantic;EEA)in this study.In the ECS,limited studies exist on ecotoxicological risk,spatial distribution and degradation rate of persistent organic pollutants(POPs)in marine organisms and sediments.In recent years,fewer researches relating to paleoceanography studies have been done in the EEA compared to North and South Atlantic based organic biomarkers which provide information on paleoceanographic variability.To fill these gaps,this thesis aim to(1)evaluate the spatial spreads,potential biological risk and historical usage in marine organisms and surface sediments based on POPs concentrations in the ECS and its estuaries to serve as baseline information for the local authority in China and(2)investigate molecular compositions of organic biomarkers and infer climatic mechanisms governing sea and land surface conditions in order to improve the understanding of the effect of climate change in the EEA.The thesis consists of three studies,of which results are presented in three manuscripts.In the first study,a wide variety of POPs from the ECS and its estuaries were predominated with low-chlorinated biphenyl congeners and hexa-chloro cyclo-hexanes.In addition,ecotoxicological risk estimate on sediments indicated that polychlorinated biphenyls(PCBs)and dichloro diphenyl trichloroethanes(DDTs)concentrations are likely to have adverse effects on bottom dwelling organisms.The bioaccumulation assessments in marine organisms were below a significant health risk to consumers.The varying levels of organochlorine compounds found in organisms do not depend solely on the bioavailability but probably also on metabolism and elimination.The isomeric ratios of DDT and its metabolites indicated a fresh input of DDTs around Hangzhou Bay.The POP residues in both marine sediments and organisms were persistent overtime,posing a long-term risk to the marine ecosystem and human via the food chain.In the second research,a marine sediment gravity core DY26?-Nig-S71GC8(1.75 m long;4066 m water depth)from the EEA deposited over the last 50 kyr was analyzed for organic carbon(Corg)content,organic carbon isotope(?13Corg)composition,lignin phenols abundance and its associated indexes.Bulk Ntot/Corg values of 0.14 to 0.02,?13Corg values of-16.7‰ to-22.4‰ and ?8 values of 0.20 to 4.29 mg/100 mg organic carbon(OC)indicate a mixed source of marine,soil and plant OM.A source plot of lignin phenol component ratios.C/V vs.S/V,further reflected a dominance of non-woody angiosperm plants during marine isotope stage 3(MIS 3)and a mixture of soil OM and non-woody angiosperm plants during the last glacial maximum(LGM)and pre-LGM.The degradation index,estimated from the(Ad/Al),ratio,indicated that highly biodegraded plant material was preserved in the core during late MIS 3,pre-LGM and post-LGM,while less degraded particulate material was deposited during the Holocene and early MIS 3.A three-end-member mixing model,using 13Corg and ?8,as well as a mass balance,was constructed to estimate relative contributions of OC fractions from different sources which,reflect a dominance marine OM proportion with a mixed fraction of soil and plant OMs over the past 50 kyr.The age profile of the lignin abundance(?8),component ratios(C/V and S/V)and degradation index estimated from(Ad/Al)v further reflected dominant proportion of terrigenous organic matter(OM)mainly of non-woody angiosperm tissues,transported to the deep sea and well preserved mostly during the marine isotope stage(MIS)3.The ?13Corg distribution reflected pronounced cyclic changes that inferred several origin of OM input to the sediments.Correlation between ?g value and ?13Corg composition further revealed that high dilution of marine OC by terrigenous OC,indicated large sediment transport to the deep sea through debris flow or turbidity current during the MIS 3.The ?8 proxies reflected the idea that soil and plant OM were important sources of TOM and it can be used to trace input of TOM,especially soil OM,to the deep sea sediment.In the third study,long chain odd numbered normal alkane(n-alkanes)parameters derived from leaf wax coating of terrestrial plants were used to elucidate past C3 and C4 vegetation changes.As the relative distribution of C3 and C4 plants may be affected by multiple climatic factors including atmospheric CO2 concentration(pCO2)and climatic conditions(e.g.aridity,temperature),the relative importance of these factors in controlling the long-term dynamics of tropical African vegetation is still debated and may differ greatly in different regions.By using n-alkane parameters records from the eastern Equatorial Atlantic(EEA)sediment gravity core,we evaluate the vegetation changes spanning the last 50 kyr BP,with respect to climatic factors.The results based on average chain length and carbon isotopic composition of the dominant n-alkanes show a clear difference of plant type for the Late Pleistocene(C4 plant domination,average 70%)and the Holocene(C3 plant domination,average 40%C4).Conversely,short-term climatic event(e.g.Heinrich Stadial)is not reflected by the vegetation changes in the core samples.We propose that the C3 and C4 plant abundances in adjacent hinterland of the EEA is mainly controlled by precipitation,which in turn is associated with the wet season length.On the other hand,it is likely that pCO2,which is normally an important factor for plant photosynthesis,may have less important influence on the C3 and C4 plant abundances in the West Africa,however more studies with high resolution are necessary in this region to examine possible connections between past vegetation changes and potential controlling factors both on orbital time scales and suborbital time scales.Overall,the studies of this thesis document(1)distribution and ecotoxicological risk of POPs in the ECS surface sediments and found that low POPs concentrations are persistent overtime,posing a long term risk to marine ecosystem and(2)the organic biomarkers composition in the EEA gravity core sediment and discover a close relationship between the organic biomarkers,paleoceanography and climate variability,which is important to improve the understanding of the coupling mechanisms governing EEA climate.