The Distribution Of Microbial GDGTs In Soil And Bone And Feasibility Analysis Of Paleoenvironment Application In Western China

The chemical name of GDGTs is known as Glycerol Dialkyl Glycerol Tetraethers(referred to as GDGTs)and is a kind of lipid compound derived from microbial ce ? membranes.GDGTs are commonly found in various extreme or non-extreme natural environments and which are ideal for biomarkers.GDGTs have been used as a flourishing organic biomarker for the quantitative reconstruction of paleoenvironment for nearly a decade(Including TEX86,BIT,MBT,Indexl,Ri/b,etc.),And based on the distribution of GDGTs in different environmental carriers such as soils and lakes,and scholars applied them in the local paleoenvironment reconstruction.However,the scholars were less systematic and comprehensive process of modern western China GDGTs involving the distribution of environmental information in the past in the investigation GDGTs when the proxies of GDGTs were applied to reconstruction;Whether in this special local area can be used directly before the scholars have established GDGTs climate and other environmental indicators to rebuild the past climate and other environmental information?In this regard,we survey these GDGTs from soils samples in different temperature,altitude,rainfall gradient in western China.In addition,For how to more accurately speculate the climate and environment information in the ruins of the ancient environment information,especially at that time some of climate and environment has not yet had an accurate answer.In this paper,we selected and discussed whether the animal bones can be used as a new type of vector for GDGTs to solve the two main problems that arise when the lipid biomarker GDGTs reconstruct the paleoenvironment:the problem of age and the climatic representation of the reconstructed climate?The following conclusions were drawn:(1)The compounds of GDGTs were investigated and analyzed in different temperature and rainfall gradients and different altitude in western China.It was found that the overall concentration of all the samples in the studied line was larger,On the one hand,GDGTs have a different degree of responsiveness to the environment,even in alkaline(pH=8±0.5)environmental conditions.On the other hand,the content of GDGTs in the local environment is not only Controlled by temperature,precipitation,humidity,soil acidity and other environmental conditions,may also be associated with the source of GDGTs in the soil and its own degree of decomposition.(2)We found that by surveying different temperature gradients the distribution of isoprenoid Glycerol Dialkyl Glycerol Tetraethers,the relative content of iGDGT-0 in the larger different temperature gradient,and other iGDGTs series of compounds is not very different.in the temperature gradient of-3 ?to 10? which was iGDGT-0>Crenar chaeol>iGDGT-2>Crenarchaeol>iGDGT-3,And in the temperature gra-dient of 10? to 15 ?,Crenarchaeol>iGDGT-0>iGDGT-2>Crenarchaeol '>iGDGT-3Crenarchaeol>iGDGT-0>iGDGT-2>Crenarchaeol'>iGDGT-3.Besides,The microbial population of the series of compounds iGDGT-1,iGDGT-2 and iGDGT-3 in the regional environment of this study is mainly the biological source of the species of Thaumarchaeota.There are groups of GroupI.Ib,which also exist in GroupI.Ia and GroupI.Ib.(3)The branched Glycerol Dialkyl Glycerol Tetraethers in the study area were predominantly 6-methyl branched Glycerol Dialkyl Glycerol Tetraethers,predominantly with ?Ia 'and ?a'.In all the samples in this study area,the series of compounds of bGDGTs of bacteria were not detected except for ?c at each temperature gradient.The other remaining 14 series of bGDGTs compounds were detected,including la,Ib,Ic,?a,?b,?c,?a,?b,?c,?a',?b',?c',?a',?b',?c'.Among them,the relative content of bGDGTs was the largest,and the relative content of ?a' of bGDGTs was not higher than that of bGDGTs,which was 17.7%?46.5%and ?a',accounting for 7.9%?46.9%And the content of 6-methyl bGDGTs was higher than that of 5-methyl bGDGTs at each temperature gradient.In addition,there is a large difference in the relative content of ?a,?b,?a,?a',?a,and ?a' between-2? and 0? with respect to other temperature gradients.(4)By analyzing the feasibility of the environmental indicators TEX86,BIT,Ri/b,MBT,Index 1 Which were established by GDGTs in other natural environments.we found that,the TEX86 index is not suitable for the temperature reconstruction in this study area.BIT value is 0.1-0.8,which is not as close to 1 or 1 that is different from the BIT values in the soil studied earlier.So the use of BIT values in the water environment of arid zones as tantalum organic inputs should be cautious.In this study,the author investigates most of the arid regions with rainfall below 400mm.The results show the difference of Ri/b is large.However,it is worth noting that in this study area is arid and alkaline,and the value of Ri/b is different.The reason may be that the adaptation of different strains of GDGTs series compounds in the local arid environment is different from the environment,which leads to the content of iGDGTs and bGDGTs is different.Not all terrestrial environments can be reconstructed using the methylation index established by the bGDGTs series of compounds.It should establish and correct the indicators according to the local environmental characteristics of the environmental samples,rather than selecting the indicators suitable for the local environment and reconstruct the paleoenvironment information.The temperature and altitude of the region have a good correlationwith Index 1;In addition,the use of indicators Index 1 temperature correction formula:Indexl-T=5.05+14.86×Indexl,the recovery temperature and the measured temperature of the weather station is also more significant correlation.The results suggest that we need to distinguish between 5-methyl bGDGTs and 6-methyl bGDGTs in the use of GDGTs to reconstruct environmental information.The appropriate indicators are calculated and still need to be investigated in different environmental samples GDGTs,and look for environmental indicators that are more appropriate for each local area.The other reason is also not ruled out the natural geographical conditions of the study area,such as the strong winds,the climate is arid and the GDGTs in the soil of the region are blowing from other places and leading to the use of existing indicators can not be derived GDGTs Indicators of application advantages in the region.(5)we found that in these three groups of animal bones from different burial conditions,different historical periods and different species are iGDGTs content of more than bGDGTs contents,compared with animal bones in BarKol ruins and Tong Wan City,the animal bones near Yu river,bGDGTs is more abundant.It is suggested that the study of GDGTs is based on skeletons.The environmental factors of water should also be taken into account.The apatite in the bones plays a buffering solvent and maintains at a relatively stable weak alkaline environment,so the pH of all skeletal samples is closer to between 7.8-8.1.Often the distribution of bGDGTs in soils is affected by temperature,precipitation and pH factors.Since bones can provide a relatively stable weak alkaline environment,bGDGTs in bones are less affected by pH,relative to soil,It may better indicate the temperature(or precipitation)changes.