Verification Of Adsorbability Of Clay Minerals To BGDGTs And Its Environmental Implications

The temperature fluctuation in the past and its influencing factors are the basis for understanding current climate change and predicting future trends.The quantitative paleo-temperature records are the key to this kind of studies.During the past decades,bGDGTs has become one of the most important biomarkers in terrestrial paleo-temperature reconstruction.A large number of studies have shown its validity in paleo-temperature reconstruction and discussed its influencing factors.However,few studies focus on the occurrence of bGDGTs in the transfer process from soil to lake/ocean.Meanwhile,the relationship between bGDGTs and organic-mineral complex is still unknown.Therefore,this study chose various soils from China,the riverine sediment from Huanghua,Hebei Province,and a static adsorption experiment,to check out the occurrence in soil,the spatial heterogeneity of bGDGTs in riverine sediment and verify the adsorption of clay minerals to bGDGTs.The following conclusions can be obtained:(1)Seven national wide distributed soil(NST1-6 and Beijing Olympic forest park soil)were separated to three subset according to its density(?<1.6 g/cm~3?1.6g/cm~3<?<2.2 g/cm~3and?>2.2 g/cm~3),the results indicate that most bGDGTs are mainly based on mineral surface adsorption(C component).Component B of NST-2,NST-5 and Beijing Olympic Forest Park soil samples contain Ia and IIa,indicating that bGDGTs may enter the mineral layer.The bGDGTs compositions in component B are closer to the whole sample,indicating that bGDGTs entering the clay mineral layer is more stable than adsorbed by the mineral surface and free bGDGTs.(2)The grain-size classification of riverine sediment in Huanghua coastal zone(coarser than 120 mesh,120-200 mesh and less than 200 mesh)shows that bGDGTs have relatively uniform distribution among each grain size components,indicating that bGDGTs are well mixed in fluvial sediments and the distribution characteristics of bGDGTs stored in continental margin sediments are insensitive to different particle transport processes.(3)The bGDGTs static adsorption experiments of montmorillonite and kaolin showed that montmorillonite and kaolin both had adsorption effect on bGDGTs,and the distance between layer in montmorillonite increased significantly after adsorption.The results showed that montmorillonite had stronger adsorption ability than kaolin,and part of bGDGTs could entered the montmorillonite layer.The results of this study are of great significance to understand the migration and transformation process of bGDGTs.They may also shed light on construction of bGDGTS-temperature transformation equation,and the application of bGDGTs in paleo-environmental studies.