Holocene Temperature Record In Glycerol Dialkyl Glycerol Tetraether Compositions Of The Gushantun Peat Sequence

Recently, global climate change has a huge impact on our living environment and ecological system, such as extreme weather, melting ice, rising sea level, deteriorating ecological environment, which makes people realize the importance and urgency to deal with climate change. Therefore, global climate change is a major scientific issue which has received increased attention across the world. Compared with other archives, peatlands are characterized by high resolution, wide distribution, continuous deposition, few external disturbance and abundant biological information. Therefore, they are important archives for the reconstruction of millennial-scale climate change. Crucially, the rate of peat accumulation is sensitive to change in precipitation and temperature. Glycerol Dialkyl Glycerol Tetraethers?GDGTs? extracted from peat deposits have been shown to be powerful tools in the reconstruction of past climate change. As the main component of the microbial membrane lipids, GDGTs'structures and compositions are very sensitive to environmental&climatic changes.The application of GDGTs preserved in peat deposits in reconstructing either climatic or biogeochemical conditions has lagged behind their application in marine and lacustrine sediments. It is now recongnised that a variety of archaeal and bactieral lipids in peats. Therefore, this dissertation will focus on the peatland from Gushantun region in the northeastern China, which is one of the most sensitive areas to global change. The compositions and distributions of GDGTs in Gushantun peats have been detected by high performance liquid chromatography-mass spectrometry ?HPLC-MS?. The distributions and compositions of GDGTs, and microbial communities have been discussed. The environmental and climatic indicators obtained from oceans, lakes and soil have been applied to this peats, to reconstruction Holocene climate change and to evaluate their applicability based on the reliable AMS¹⁴C dating. And also importantly, this research will fill the gaps about biomarker research in the study area. The main results are as follows:?1?Microbial assemblages are abundant in Gushantun peats, including methanogens, ammonia-oxidising Thaumarchaeota and anaerobic bacteria. Compared with the archaea, anaerobic bacteria are more suitable to survive in the study area;?2?Abundance of bGDGTs varies similarly with that of iGDGTs. The ratios of iGDGTs to bGDGTs with depth may indicate there are many fluctuations of microenvironment in peat bogs since the last deglaciation;?3? TEX₈₆ does not apply to establish the environment changes in Gushantun peats;?4? The cyclization ration of bGDGTs ?CBT?-derived pH values are 4.7-6.7, and the pHCBT' values of ?De Jonge et al,2014? are 4.6-6.8. They both are close to the measured peat pH in the study region, suggesting the pH proxies based on CBT are reliable;?5? The methylation index of bGDGTs and cyclization ration of bGDGT ?MBT'-CBT?-derived the mean annual air temperature ?MAT? values have the same changing trend with MAT_mr values of ?De Jonge et al,2014?. Two indicators can reflect the mean annual air temperature variation in Gushantun region since the last deglaciation. There are three stages: the temperature rise of the early Holocene, the Holocene megathermal and the cooling of the late Holocene. In addition, six cooling events are found in Gushantun region and could be correlated well with the ice-rafted debris ?IRD? events in the North Atlantic on the centennial to millennial timescales. MBT'-CBT-derived MAT values are higher than present mean annual temperature, and MAT_mr values are close to present mean annual temperature in Gushantun region. Taken together, the global soil calibration of ?De Jonge et al,2014? appears to be applicable to MAT estimates in Gushantun, Northeastern China;?6?The reconstruction of the paleo-climate sequences in our study are consistent with the results of pollen, phytolith and ?¹³C time series of the plant remain cellulose from the same area. It indicates that it is applicable to reconstruct the temperature sequence in Gushantun peats based on bGDGTs proxies.