The early Holocene optimum inferred from a high-resolution pollen record of Huguangyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that (i) pollen percentage of trees and shrubs reached 56% during the early Holocene (11600―7800 cal a BP), of which the pollen percentage of tropical trees reached a maximum at 9500―8000 cal a BP, reflecting a hot and wet envi- ronment; (ii) during the mid-Holocene (7800―4200 cal a BP), the pollen percentage of montane conif- erous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indi- cating lower temperature and humidity; (iii) in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500―8000 cal a BP in south- ern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer mon- soon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

The early Holocene optimum inferred from a hish-resolution pollen record of Husuansyan Maar Lake in southern China

A high-resolution pollen record of the past 13000 a from Huguangyan Maar Lake reveals the vegetation and environment changes in southern China during the Holocene. It shows that （i） pollen percentage of trees and shrubs reached 56% during the early Holocene （11600-7800 cal a BP）, of which the pollen percentage of tropical trees reached a maximum at 9500-8000 cal a BP, reflecting a hot and wet environment; （ii） during the mid-Holocene （7800-4200 cal a BP）, the pollen percentage of montane coniferous trees and herbs increased, while the percentage of tropical-subtropical trees decreased, indicating lower temperature and humidity; （iii） in the late Holocene spanning from 4200 to 350 cal a BP, the pollen percentage of herbs and montane conifer increased significantly, indicating a marked decrease of temperature and humidity. Our pollen data reveal that the time period 9500-8000 cal a BP in southern China represents a climatic optimum for the Holocene characterized by hot and wet conditions. This is consistent with the Holocene optimum found in lower latitude regions globally. We speculate that strong insolation might cause the northward migration of the ITCZ and subtropical summer monsoon front, which resulted in an early Holocene optimum in the Huguangyan area. The dry tendency and climate fluctuations of the middle and late Holocene could be associated with a decrease in solar insolation and frequent ENSO event.     

High—resolution records of Holocene from the Shuangchi Maar Lake in Hainan Island

The results of sedimentary characteristics,grain-size,clay mineral,C/N and pollen analysis reveal the evolution history of the Shuangchi Maar Lake of Hainan Island as well as the short-term climate variations in tropical areas.It is testified that the Maar sediment system was sensitive in recording the rapid climate changes in the Holocene.These multidisciplinary results demonstrate that the thermal maximum in the Holocene climate lasted from 7200 to 2700 aBP,with serveral abrupt ephemeral vibrations occurring between 7250-6120aBP and at around 4460,3850 and 2700 aBP.In the late Holocent,particularly at -2700 aBP,a distinct environmental change indicating an important climate transition in the tropical eastern Asia was recorded,probably responding to the enhancement of ENSO phenomena in the Pacific Ocean.In addition,the high-resolution algae record clearly indicates periodical climate fluctuations at 500 a cyclicity during the last 2500 years.     

High-resolution climate evolution derived from the sediment records of Erlongwan Maar Lake since 14 ka BP

Varve counts with AMS 14 C,137 Cs and 210 Pb dating of sediments(0-900 cm) from Erlongwan Maar Lake,NE China were used to establish a high-resolution chronology series for the late Quaternary.Dry density,total organic carbon(TOC) content,total nitrogen(TN) content,TOC/TN ratios and stable organic carbon isotope(13 C org) ratios were continuously analyzed on this sediment profile.On the basis of lithological characters,sporo-pollen assemblages and geochemical analyses,we identified 6 climate stages within the last 14 ka BP.The time before the Holocene(14-11.4 ka BP) represents a higher-order oscillation climatic transitional period(I).The entire Holocene climate development(from 11.4 ka BP to present) exhibited an increasing temperature trend,although there were cold and warm alternations(II-VI).The periods included were:II(11.4-9.05 ka BP) warm-wet stage,III(9.05-7.4 ka BP) cold and warm fluctuation stage,IV(7.4-4.2 ka BP) smoothly warming climate stage,V(4.2-1.67 ka BP) climate optimum stage,and VI(from 1.67 ka BP to present) cool and drier stage.Each climate stage began with a warming event and ended with an abrupt cooling event.This climate change cycle had unequal time spaces that were progressively shorter over time.Several abrupt climate shifts occurred at about 9.4-9.05,8.5-8.2,7.8-7.4,4.6-4.2,3.7-3.25,2-1.67 and 0.3-0.03 ka BP.Thus,it can be seen that the climate has been warming since 1920 AD,which indicates a new climate stage.     

青藏高原全新世气候变化研究进展

青藏高原是世界上最高、最年轻的高原，它对北半球的气候变化有重大影响。全新世是与人类进化、人类文明形成最密切的时期。分析、总结了青藏高原全新世的气候环境变化的研究成果，并对这些成果进行讨论。高原的全新世大暖期来临于10kaBP，鼎盛期为7—6kaBP，大暖期时，高原植被、森林扩大，泥炭发育，湖面上升，夏季风增强。大约在5kaBP，高原气候由暖湿向冷干转变。     

广东的气候变化：气温,降水和日照

根据广东４７个测站１９５４～１９９０年逐年１月和７月气温、降水和日照时数的标准化资料作ＥＯＦ、周期和线性回归分析，得到：①各要素最重要的空间分布型式（ＥＯＦ１）是表示全省各地变化位相相同的分布，其中气温ＥＯＦ１的分布最为均匀，而且各要素的ＥＯＦ１在１月的分布也较７月的分布规则．②近４０年来全省性气候变化有一定的周期性特点，其中尤以二月份气温的７ａ周期变化最为显著．线性回归分析表明广东气候变化基本上是稳定的，没有明显的线性增、减趋势．③广东各要素的极端异常变化可能与Ｅｌｎｉｎｏ有密切关系．     

关中盆地LGT全新世剖面N含量及其环境意义探讨

通过对关中盆地LGT全新世剖面的土壤全氮(TN)含量分析研究发现,全氮在黄土、古土壤中的含量明显不同,黄土中均值0.294 0 g/kg,古土壤中均值0.385 6 g/kg,在剖面上呈现出明显的高值和低值交替变化的特征,这种变化与磁化率曲线可进行良好的对比,且与土壤-黄土序列对应也良好.认为全氮可作为一个气候替代指标.全氮含量高指示暖湿的生物活动强的气候条件,反之,含量低则指示冷干的生物活动弱的气候条件.     

安固里淖全新世湖面变化及其环境意义

地貌证据和钻孔沉积特征分析表明,安固里淖全新世湖面变化分为４个时期：湖面快速上升时期（１００００～７３００ａＢＰ）,高湖面时期（７３００～６２３０ａＢＰ）,湖面快速下降时期（６２３０～５３００ａＢＰ）,湖面波支动性下降时期（５３００ａＢＰ以来）,其中高湖面达到现代湖面以上２８ｍ的位置,代表全新世气候最暖湿的时期。安固里淖全新世湖面变化及其反映的气候变化,与邻近地区具有良好的对应关系,其高湖面与中国     

渭北旱塬黄土记录的晚冰期以来短尺度气候变化

通过对长武下孟村黄土剖面的野外考察和磁化率，粒度，吸湿水含量分析，探讨了该地区晚冰期以来气候变化规律，研究结果表明，该剖面较好地记录了新仙女木期（YD）和博令－阿勒罗德事件（BL＋AL）短尺度较小幅度气候变化事件，对应全新世气候最适宜期（8500－3100a.BP)，该地为黑垆土成壤期，从3100a.BP开始，季风气候格局快速转变，气候干旱化，土壤和土地资源退化，所以3100年来该地区形成了弱成壤的土壤层和黄土层。     

Palaeoclimatic evolution recorded by multidicipline in sediments in gahai lake, qaidam basin since late last deglacial

Based on the analyses of Loss-on-Ignition (LOI), carbonate content and sediment characteristics, this paper reconstructs the climatic and environmental evolution of the Gahai Lake area since the late Last Deglacial Period.The results cover the late Last Deglacial Period and the Holocene.The climate was very unstable and rather arid during the late Last Deglacial Period.The Holocene can be divided into three pe-riods:the early Holocene (11360-8240 cal aB.P.), which was dry but unstable and featured rising tem-peratttres, the mid-Holocene (8240-3200 cal aB.P.), which was warm and wet and the late Holocene (since 3200 cal aBP), which was cold and dry.Results also show a warm-wet event around 1500 cal aB.P.     

巴尔喀什湖流域气候变化特征分析

根据巴尔喀什湖流域5个气象站20世纪的逐月气温和降水资料,利用滑动平均法和差积曲线法,分析流域20世纪的气候变化特征及其与巴尔喀什湖自身水文特征的联系,并从能量转换角度进行解释.结果表明:空间上,年均气温从南向北、从东向西逐渐降低,年际变化从南向北变大;年降水量从四周向中心腹地逐渐减小,年际变化从北向南变大.时间上,年均气温总体上升且大致具有10~23 a的周期性;年降水量整体上表现为增长,20世纪90年代初期略有减少.年内月均气温的最低和最高值分别出现在1月和7月,且低温月份气温上升趋势较高温月份明显;降水量的年内分布呈双峰型.20世纪50年代中期至70年代中期,整个流域的气候要素变化较大.     

Holocene volcanic rocks in Jingbo Lake region ? Diversity of magmatism

During the time from 5500 a to 5200 a BP more than 10 Holocene volcanoes in Jingbo Lake region erupted and the volcanic rocks covered an area of about 500 km2. Holocene volcanic rocks in Jingbo Lake region belong to the potassium?rich rocks and contain three rock types: trachybasalts, basanites and phonotephrites. Various types of magmatism formed in a small area and in a short period of time came from partial melting of potassically?metasomatised lithospheric mantle. The diversity of magmatism can be explained by that Jingbo Lake is situated in the back?arc extensional region of East Asian continent subducted by the Pacific Ocean, and potassic fluid derived from mantle wedge or dehydration of subducted slab can result in a high heterogeneity of the mantle beneath this region. Based on the pressure estimation of clinopyroxene megacrysts, we estimate that phonotephrite magma fractionally crystallize at ca. 52?54 km down the earth.