Liu Qiang

A 1600 year multiproxy record of paleoclimatic change from varved sediments in Lake Xiaolongwan, northeastern China

[1]xa0A multiproxy record from Lake Xiaolongwan, northeastern China, reveals distinct stratigraphical patterns in organic carbon, total nitrogen, organic carbon isotope, nitrogen isotope, clastic content and dinocyst concentration, over the past 1600 years. High atomic C/N ratios in the sediment suggest that a large amount of organic matter in the sediments is derived from vascular plants and soil in the catchment. Based on the good agreement between cyclical variations of δ13Corg in the sediments and the spring drought index from historical documents, we interpret that the variation of δ13Corg in the sediments is an indicator of humidity or precipitation in the study area. Several notable drought periods with heavier δ13Corg occurred during AD 490–570, AD 780–990, AD 1360–1450, AD 1590–1670 and the last 150 years. These century-scale drought episodes correspond to solar activity. It suggests that solar forcing plays an important role for the δ13Corg variation in the sediments through driving the changes in humidity/vapor pressure deficit. Dinocyst concentration is high during most of the Medieval Warm Period, and low during the European Dark Age and the Little Ice Age. The increase in dinocyst concentration is generally synchronous with decrease of δ15N value. The δ15N values in the studied lake are most likely influenced by the duration and intensification of lake overturn, which regulates the amount of depleted δ15N nutrients (dissolved organic nitrogen and ammonium) and dinoflagellate blooms.

Vegetation history and climate change recorded by stomata evidence during the late glacial in the Great Khingan Mountain Region, Northeastern China

The research on the evolution of larch forest is significant to nunderstand the vegetation and climate change in mid-high latitude nregion of the Northern Hemisphere. However, the pollen records to nreconstruct the larch forest are problematic due to low pollen representation ncaused by severely poor pollen productivity and dispersal. New proxy nof microfossils is needed to solve this problem. Using coniferous nstomata as a proxy to reconstruct the evolution of conifers has some nadvantages, such as well preserved, locally deposited, continuously nremained in lake sediments and can be accurately identified to the ngenus level. Therefore, a high-resolution stomata record covering n20.3–10.8 cal ka BP from Lake Moon was presented, in order nto reconstruct larch forest history from the Last Glacial Maximum nto early Holocene in the Great Khingan Mountain Region, Northeast nChina. Reference conifer stomata from fresh leaves of the local coniferous nspecies and lake surface samples were prepared for the identification nof the fossil stomata. Larix , Sabina and Picea stomata were identified from the sedimentary nsequence of Lake Moon, and the results of stomata influx from this nstudy and pollen influx from the previous study indicate that the nvegetation evolution has gone through distinct stages. Before 15.0 ncal ka BP, no Larix existed in the vicinity of study nsite. The first arrival of larch is inferred by the continuous presence nof stomata at 15.0 cal ka BP, which manifests that the vegetation nturned into forest steppe. The coverage of forest increases slightly nfrom 15.0 to 12.8 cal ka BP with an interruption between 14.3 and n14.0 cal ka BP. During 12.8–11.8 cal ka BP, the vegetation nwere characterized by the expansion of conifers mainly Larix and the shrinkage of broadleaves and herbs. From 11.8 to 10.8 cal nka BP, the vegetation type remained as forest steppe with the shrinkage nof conifers dominated by Larix , in conjunction with nthe expansion of broadleaves and herbs with high vegetation coverage. nThe establishment of larch forest inferred by the continuous presence nof stomata marks the onset of the late glacial in the Great Khingan nMountain Region at 15.0 cal ka BP. The application of stomata analysis nprovides detailed scenes of coniferous evolution surrounding the Lake nMoon. It is suggested that the analysis of fossil stomata is a valuable ntool to demonstrate unambiguous evidence for the local presence of nthe conifers in study region, even better than pollen records when nthe component of larch is low in vegetation. The evolution of the nforest communities in the late glacial period in the Great Khingan nMountain Region is comparable with the vegetation evolution of other nregions at different latitudes in East Asian monsoon region, which nindicates that the climate change at millennial/centennial scale in nlate glacial is roughly synchronous in East Asian monsoon region. nThe series of climatic periods in this study revealed by the stomata nand pollen records is also similar to that of Europe, like Meiendorf ninterstadial, Oldest Dryas cold event, Bolling-Allerod warm nphases, Younger Dryas cold event, warm and humid early Holocene. The ntemperature change is probably the main factor to impact the vegetation nchange. The study shows that the vegetation succession in the study narea is responsive to the temperature change of the Northern Hemisphere ncontrolled by the global ice volume, and reveals the synchronization nof the late glacial climate change in the mid latitude region of East nAsia and the North Atlantic region.

火山灰全岩与原位分析差异：以四海龙湾记录的1 600年前金龙顶子火山喷发为例

火山灰地层学主要依靠火山玻璃的成分进行源区的识别，然而，当火山玻璃成分不均一时就会对源区识别造成影响.四海龙湾玛珥湖位于东北新生代龙岗火山区内，其湖泊沉积物可以记录周边的火山喷发，电子探针等方法得到的火山玻璃成分可以揭示其喷发来源.同时，玛珥湖的纹层年龄可以限定其喷发年龄.在四海龙湾沉积物(钻孔2008) 的78~79 cm岩芯处出现一层火山灰层，其纹层年龄为AD 308 a，电子探针结果显示火山玻璃具有不均一的主量元素组成，为玄武质粗安岩到碱玄质响岩.FeO、TiO2及Al2O3等与MgO协变图解更清楚地显示了此次火山喷发的火山玻璃成分的不均一性.火山玻璃与火山灰全岩对比分析显示，全岩分析在火山灰地层学应用中容易造成对比偏差.