Research On The Distribution Of The Phytolith In Surface Soil And The Reconstruction Of Temperature-humidity Pattern During The Holocene In Northeast China

Phytolith analysis has been widely used in paleo-environmental reconstruction since the Quaternary.The key point of phytolith analysis is the correct interpretation of the phytolith assemblages in sediments.Thus,studies on the modern process of phytolith is necessary for understanding the environmental implication of the phyolith objectively and scientifically.In this study,according to the natural gradient of the environmental factors,we collected 246 topsoil samples along annual temperature isotherm of 0?,4?,8? and annual precipitation equipluve of 400 mm,600mm.With the special sampling method,I targeted to reveal the responses of phytolith assemblages to a single environmental factors(i.e.temperature or participation).Then several phytolith types,which were very sensitive to the variation of temperature and precipitation,were selected to define the warmth index and moist index.Based on the indexes,the quantitative relationship between phytolith assemblages and temperature(or precipitation)were built.Four peat profiles(i.e.Hani,Gushantun,Huanan and Shuangyang)collected in Northeast China were cored and sub-sampled.In total,156 samples for phytlith analysis,56 samples for pollen analysis and 136 samples for grain size were analyzed.With the quantitative transfer functions,I reconstructed the paleo-temperature and paleo-precipitation of the four sections.Additionally,the paleoenvironmental reconstructions of grain size and pollen analysis were adopted to verify the reliability of the phytolith environmental factors model.Moreover,combined with some digitized pollen diagrams of 5 profiles,we recalculated the paleo-temperature and paleo-precipitation at different stages during the Holocene.Finally,the period and tendency of the paleoclimate in Northeast China were discussed employing the spectral analysis and the accumulative anomaly analysis.The main conclusions are listed as follows:1.There are a large number of phytoliths with various morphotypes in the topsoils in Northeast China.In this study,19 kinds of phytlolith morphotypes were identified.They were elongate,lanceolate,rondel,trapeziform polylobate,saddle,bilobate,square,bulliform,vertebra type,bow type,conduit,silicified plant tissue,silicified stomata,tile,papillae,prism,polyhedral type,polyhedral epidermal phytolith and sponge spicule.Among which,lanceolate and the square were sensitive to the temperature while the saddle was sensitive to precipitation.The elongate was sensitive to both temperate and precipitation,but was more sensitive to precipitation.2.In the paper,we built a new phytolith-based temperature index which reflected the temperature versions,expressed as I=square/(square+elongate+lanceolate).After making comparisons with climatic index and warmth index,we found that all these indexes can be used for quantitative paleo-temperature reconstruction.The fomulas can be expressed as y=8.54x+2.81 ? y=-3.61x1+6.52 ? y=7.42x2+2.20.In this study,we have also built a phytolith-based moist index,expressed as bilobate/(bilobate+elongate).It tracked the variation of precipitation better than the arid index which was not suitable in this area.Thus,we built the quantitative function between the phytolith-based moist index and the annual precipitation which was expressed as y=-229.02x+597.83.3.We can reconstruct the paleoclimate in Northeast China effectively according to both temperature-phytolith transfer function and phytolith-based warmth index(or reconstruct the precipitation using precipitation-phytolith transfer function and phytolith-based moist index.However,the quantitative relationship between phytolith-based warmth index and annual temperature is more suitable for paleo-temperature reconstruction in this area.And the precipitation-phytolith transfer function is more suitable for paleo-precipitation reconstruction.The reconstructed paleo-temperature and paleo-precipitation in Hani and Huanan area showed a good agreement with the temperature rising period in the early Holocene,the middle Holocene warm period and the cold period in late Holocene.Additionally,Hani and Huanan peatlands recorded a series of cold events which may corresponded to the global IRD6~IRD1 events.These results revealed that the phytolith based warmth index and the phytolith-based moist could greatly tracked the climate change tendency and some important climate events in NE China during the Holocene.This indicated our poleo-climate models are effective.4.During different periods in the Holocene,the areas with high value of the paleo-tempertature located at the south-east part of the Northeast China while the low value areas at the north-west part.This indicated a fact that the temperature decreased from the southeast to the northwest of Northeast China.At the time node of 10.0 cal.ka B.P.,8.0 cal.ka B.P.,6.0 cal.ka B.P.,4.0 cal.ka B.P.,the areas with high precipitation located at the north-east part of the Northeast China while the low value areas located the north-west of the Northeast China,this revealed that the precipitation decreased from the north-east to the north-west in Northeast China;at the time node of 2.0 cal.ka B.P.and 0.0 cal.ka B.P.,the areas with high value of the paleo-precipitation have moved,so the precipitation decreased from the south-east to the north-west.5.The poleo-temperature of the Northeast China have been increasing while the poleo-precipitation was decreasing since the Holocene.We have identified many paleoclimatic periods with different time scales,such as 5520 a,3950a,3150 a,1520a,990 a,340a and 220 a.The sub-orbital scale climatic period revealed by Hani and Huanan peat profiles were comparable with previous researches.Additionally,in the next 50 years,the climate in the Northeast China was tend to be warmer and drier.While in the next 200 or 300 years,the climate in this area tend to be warmer and humider.