A Possible Impact of Cooling over the Tibetan Plateau on the Mid-Holocene East Asian Monsoon Climate

By using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP9L-AGCM) under the Chinese Academy of Sciences, the authors investigated the response of the East Asian monsoon climate to changes both in orbital forcing and the snow and glaciers over the Tibetan Plateau at the mid-Holocene, about 6000 calendar years before the present (6 kyr BP). With the Earth’s orbital parameters appropriate for the mid-Holocene, the IAP9L-AGCM computed warmer and wetter conditions in boreal summer than for the present day. Under the precondition of continental snow and glacier cover existing over part of the Tibetan Plateau at the mid-Holocene, the authors examined the regional climate response to the Tibetan Plateau cooling. The simulations indicated that climate changes in South Asia and parts of central Asia as well as in East Asia are sensitive to the Tibetan Plateau cooling at the mid-Holocene, showing a significant decrease in precipitation in northern India, northern China and southern Mongolia and an increase in Southeast Asia during boreal summer. The latter seems to correspond to the weakening, southeastward shift of the Asian summer monsoon system resulting from reduced heat contrast between the Eurasian continent and the Pacific and Indian Oceans when a cooling over the Tibetan Plateau was imposed. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for mid-Holocene climate change in the areas highly influenced by the Asian monsoon.     

无定河流域全新世中期人类聚落选址的空间分析及地貌环境意义

以无定河流域的数字高程模型为主要研究对象,利用地理信息系统软件进行空间分析,与陕西北部无定河流域龙山时期遗址的分布位置叠置和聚类分析,讨论聚落选址与地貌类型、距河流水平距离、河网等级等6个地形地貌因子之间的关系。结果发现,全新世中期无定河流域人类在聚落选址时,对水文条件、地貌和地面坡度条件有较强的倾向性,而对地面朝向无明显倾向性。选址时选择地形地貌影响因子的优先顺序为:地貌类型、遗址距河流距离、遗址处地面坡度、遗址处河流等级、遗址处地面朝向。     

全新世中期7 ka前后降温事件对中国北方植被生态的影响

大量研究表明,随着气候变暖,全球生态环境发生了巨大变化。然而,在相对温暖的气候条件下,假若发生重大降温事件,生态环境尤其是植被生态会如何响应,值得深入探讨。利用近年来发表的全新世高分辨率古气候记录以及孢粉记录的植被变化,对全新世中期7 ka(1 ka=1000 cal.a B.P.)前后的降温事件及其对植被生态的影响进行了综合分析。结果表明,7 ka前后降温事件在北半球很大范围都有记录,在季风边缘区伴随着气候的干旱,而在西风主导的区域总体表现为气候湿润。中国北方季风区山地以及高纬度地区表现为建群种的变化,如阔叶树种的减少以及针叶树种的增加;在季风边缘区总体表现为干旱气候下植被盖度的降低;而在西北内陆山地高山区域表现为林线的降低或树种的变化,低山地区森林下限表现为森林成分的增加以及耐旱树种的减少;在山前草原和盆地荒漠草原区域,植被的响应表现为植被盖度的增加和喜湿成分的增加。降温直接影响湿度较大的高山地区的森林成分和林线高度,而在低山干旱半干旱地区,降温则通过抑制蒸发、增加有效湿度影响植被盖度和组成。由于不同钻孔年代的不确定性、不同植被类型对气候变化的敏感性不同等,不同区域发生植被转型的时间不尽一致。全新世中期7 ka降温事件的触发机制有待深入研究,可能与大型火山喷发以及太阳活动变化有关,夏季太阳辐射的持续降低以及地球系统内部反馈也是共同的原因。     

The PMIP3 Simulated Climate Changes over Arid Central Asia during the Mid‐Holocene and Last Glacial Maximum

In this study, the climate changes over Arid Central Asia(ACA) during the mid-Holocene(approximately 6,000 calendar years ago, MH) and the Last Glacial Maximum(approximately 21,000 calendar years ago, LGM) were investigated using multimodel simulations derived from the Paleoclimate Modelling Intercomparison Project Phase 3(PMIP3). During the MH, the multimodel median(MMM) shows that in the core region of ACA, the regionally averaged annual surface air temperature(SAT) decreases by 0.13°C and annual precipitation decreases by 3.45%, compared with the preindustrial(PI) climate. The MMM of the SAT increases by 1.67/0.13°C in summer/autumn, whereas it decreases by 1.23/1.11°C in spring/winter. The amplitude of the seasonal cycles of the SAT increases over ACA due to different MH orbital parameters. For precipitation, the regionally averaged MMM decreases by 5.77%/5.69%/0.39%/5.24% in spring/summer/autumn/winter, respectively. Based on the analysis of the aridity index(AI), compared with the PI, a drier climate appears in southern Central Asia and western Xinjiang due to decreasing precipitation. During the LGM, the MMM shows that the regionally averaged SAT decreases by 5.04/4.36/4.70/5.12/5.88°C and precipitation decreases by 27.78%/28.16%/31.56%/27.74%/23.29% annually and in the spring, summer, autumn, and winter, respectively. Robust drying occurs throughout almost the whole core area. Decreasing precipitation plays a dominant role in shaping the drier conditions, whereas strong cooling plays a secondary but opposite role. In response to the LGM external forcings, over Central Asia and Xinjiang, the seasonal cycle of precipitation has a smaller amplitude compared with that under the PI climate. In the model-data comparison, the simulated MH moisture changes over ACA are to some extent consistent with the reconstructions, further confirming that drier conditions occurred during that period than during the PI.     

全新世中期中国气候和东亚季风:PMIP4模式结果

利用国际古气候模拟比较计划(PMIP)最新第四阶段(PMIP4)中14个气候模式的试验数据,集中研究了距今约6 000年的全新世中期中国气候和东亚季风。与早期PMIP第三阶段(PMIP3)多模式结果类似,全新世中期中国年、冬季和春季地表气温较工业革命前期偏冷,而夏季和秋季偏暖,其中年和冬季模拟偏冷与大部分地质记录显示的偏暖不符;所有14个PMIP4模式集合的中国区域平均年和季节温度变化绝对值为0.08~1.69 ℃,较PMIP3多模式平均结果额外偏小0.01~0.45 ℃,这部分源于大气二氧化碳浓度的减少。在用于分析的11个PMIP4模式平均结果中,全新世中期中国年平均降水、蒸发和有效降水(即降水量减蒸发量)相对于工业革命前期分别增加2%、减少1%和增加7%,所有3个物理量在季节上均表现为冬春季减少,夏秋季增加。对比PMIP4模式和PMIP3多模式平均结果,上述3个物理量的中国区域平均值和区域变化差异均在夏、秋季大于年和冬、春季;相比于PMIP3模式,PMIP4模式模拟的年有效降水变化与地质记录更为接近。全新世中期东亚冬、夏季风在14个PMIP4模式中均模拟加强,所有模式平均较工业革命前期分别增强11%和32%;在区域尺度上,与早期PMIP3模式相比,当前PMIP4模式模拟的季风环流增强幅度在东亚北部更强,南部偏弱。     

中全新世黄河流域耕地格局重建及对原生植被的影响(英文)

Yangshao culture is the most important mid-Holocene Neolithic culture in the Yellow River catchment,and thus,a study on the impact of human activities on the environment is important.In the current study,the distribution pattern of the cultivated land in late Yangshao culture is reconstructed using GIS tool and site domain analysis(SDA).The results show that the cultivated land during 5.5-5.0 ka BP was mainly distributed in the Weihe River valley,Luohe River valley,northwestern Henan Plain,Fenhe River valley and eastern Gansu region,especially concentrated in the Xi’an-Baoji line of the Weihe River valley.At that time,at least 37,000 km 2 of lands were reclaimed in the middle and lower reaches of the Yellow River,and 132,000 km 2 of lands were affected by agricultural activities.Human activities had become the driving force of land use/land coverage.Charcoal records indicate that the ancestors of Yangshao culture burnt forests for reclamation,leading to the decrease of arbor pollen at 5 ka BP in core areas of the Yangshao culture.The areas that were significantly affected by human activities accounted for 3.2% of the Yangshao culture influenced area,while the moderately affected areas accounted for 20.1% of Yangshao culture influenced area.Meanwhile,92% of the land areas on the edge and outside of the Yangshao culture influenced area were not affected by human activities.The arbor pollen in these areas did not decrease until 4.0 ka BP.     

古气候模拟与气候模式

本文概要地介绍了国内外近年来古气候模拟研究的若干进展.内容包括国际古气候模拟比较计划的研究工作和中国科学院大气物理研究所开展的古气候模拟研究.作为气候模拟研究的重要手段,气候模式是非常关键的,因此,文中也对古气候模拟中使用的各种气候模式作了扼要的介绍.     

A diatom-inferred water depth reconstruction for an Upper Peninsula, Michigan, lake

Transects of surface sediment samples were taken in 4 lakes from the Sylvania Wilderness Area, Upper Peninsula of Michigan. These surface samples were compared with diatom samples from a core taken in the Northwest basin of Crooked Lake, also from the Sylvania Wilderness Area. Weighted Averaging calibration was used to reconstruct lake depths in Crooked Lake using the diatom microfossils from the core and the surface samples to infer past lake depth. During the early Holocene the lake was dominated by planktonic species and diatom-inferred water depth was large – approx. 13 m. At about 6700 BP inferred water depth was 2 m and samples were dominated by Fragilaria construens var. venter – a species characteristic of shallow parts of the surface sample transects. From 6700 to 5000 BP reconstructed water level was at its shallowest. From 5000 to 3000 BP it increased. This rise in water level was marked by increasing abundances of Aulacoseira ambigua and occurred at the same time increasing percentages of hemlock pollen indicate increasing available moisture. Modern water depth was reached about 3000 BP. The water level changes at Crooked Lake are consistent with regional climate changes in the Upper Midwest during the Holocene. The lake was shallowest during the mid-Holocene warm period documented by other investigators. It deepened as the Midwestern climate became cooler and wetter during the late Holocene.     

一个耦合气候系统模式模拟的中全新世时期亚洲季风系统变化

本文分析了一个耦合模式FGOALS_g1.0对工业革命前气候(0ka)和中全新世时期(6ka)亚洲夏季风的模拟结果。在该研究中我们主要分析季风降水变率较大的区域,即东亚夏季风区(20°～45°N,110°～120°E)和印度夏季风区(10°～30°N,70°～80°E)。尽管耦合模式的普遍偏差依然存在,该模式反映出亚洲季风系统是海陆热力性质差异的结果,并较好地模拟出了0ka亚洲夏季风大尺度环流的特点和季节变化的特征。6ka和0ka比较分析的结果表明,6ka时期欧亚大陆增暖,海陆温度梯度加强; 印度夏季风降水从南亚大陆北移到 30°N 附近,位于青藏高原南侧的降水大值中心降水加强; 东亚季风区降水则表现为华北地区减少,长江流域和华南地区降水增加的特点。但合理地模拟季风爆发仍然是耦合气候系统模式的难点之一。
6ka时期亚洲夏季风变化是和大尺度季风环流的变化联系在一起的,而其根本原因是中全新世时期地球轨道参数变化所引起的太阳辐射变化,北半球季节循环的振幅加强。海陆热力性质的差异所导致海陆温差加大使得北半球的季风环流加强,印度夏季风高空东风在 20°～30°N 加强,低层赤道东风加强,跨赤道后的西南气流向北推移,从而使得印度夏季风降水雨带北移到 30°N 附近。东亚季风区的高低空温度场的配置使得副热带高空急流减弱,位置偏南,从而有利于华北地区的高空出现异常的辐合,中层为异常的辐散,抑制了季风降水的发展; 长江流域和华南地区则相反,季风降水降水加强。     

塔里木盆地南缘和田绿洲中全新世以来气候环境变化与人类活动

塔里木盆地南缘和田绿洲约特干遗址剖面多指标综合地记录到了近6.7 ka BP以来的环境变化。考虑到此地区人类活动的历史,各指标的变化记录了自6.7—4.0 ka BP期间环境变化的自然过程,揭示出6.5—6.7 ka BP期间的显著湿润期以及出现于4.0 ka BP之后的转干和3.0 ka BP前后的相对冷湿期。自2.0 ka BP开始,人类活动的影响渐趋于显著。