Geochemistry Of Elements In A Peat Profile In Xinjiang Altai Mountain And Its Implications For Holocene Climate Change

The northeast of Altay in Xinjiang is located on the south slope of Altai Mountains.Because it is located in the western edge of the transition zone between westerly zone and East Asian summer monsoon,the factors affecting climate change in this region are complex.Reconstructing the paleoclimate in this region is helpful to understand the Holocene climate evolution history and driving mechanism in the arid area of Central Asia.Due to the influence of climate,topographic characteristics and hydrological factors in mountainous areas,palsa had been developed in some basins in mountainous areas.Palsa is an ideal geological carrier to deeply understand the change of permafrost in the region and obtain regional paleoclimate information.We collected about 4m peat profile in Sahara sand peatland.According to the results of AMS ¹⁴C dating of peat plant residues,we established the chronological sequence of peat profile based on the calibration(INTCAL13).Based on the analysis of dry density,ash content,element content(Zr,Ti,Al),total mercury content(normal temperature,30?,105?),humification degree,total organic carbon(TOC)and total nitrogen(TN)of peat samples,the development characteristics of Sahara sand palsa and the characteristics of climate change in Altay area during early-middle Holocene were discussed.The main conclusions of the study are as follows:(1)The top age of the profile is 5.3cal.ka BP and the bottom age is 10.5cal.ka BP.Based on the analysis of dry density,ash content,total content of Zr,Ti,Al and Hg in peat profile,the variation characteristics of regional atmospheric dust deposition flux in early-middle Holocene are reconstructed.The results show that the atmospheric dust deposition flux and mercury deposition flux increase abnormally at the top of the palsa(0?26cm),indicating that the palsa enters the mature or declining period at about 5.7cal.ka BP,and then the top of the palsa received long-term atmospheric dry and wet deposition.(2)By analyzing the ratio of mercury with high thermal stability to total mercury,humification degree,TOC and TN in peat profile,we reconstructed the paleoclimate evolution characteristics of Altay,which can be divided into three stages:10.5?10cal.ka BP climate changes from cold to warm and wet,10?7.1cal.ka BP climate is generally warm and dry,7.1?5.7cal.ka BP climate changes to cold and wet.The climate change characteristics in Altay during the early-middle Holocene are roughly the same as those in the surrounding areas.The ratio of mercury with high thermal stability to total mercury in peat profile indicates that four significant abrupt climate events had occurred in Altay,which occurred about 10.3cal.ka BP,9.4cal.ka BP,8.3cal.ka BP,7.4cal.ka BP,6.7cal.ka BP and 6.2cal.ka BP respectively.(3)Using the ratio of mercury with high thermal stability to total mercury,we reconstruct the temperature time series in this area.Further analysis shows that the temperature in this area has periodic fluctuations of 450a,255a,96a,74a and 68a.The period of temperature fluctuation in Altay corresponds well to the period of solar activity,indicating that solar activity may be the main driving factor of climate change in early-middle Holocene in Altay.This study provides clues for exploring the proxy indicators of paleoclimate change recorded by peat and deeply understanding the Holocene climate evolution history and driving mechanism of Altay area under the influence of westerly area.