共查询到20条相似文献，搜索用时 562 毫秒
1.
为揭示自末次盛冰期以来中国南方植被的变化规律,文章在前人工作的基础上,通过在一些研究薄弱区布钻取芯,建立钻孔剖面高分辨率的时间标尺和胞粉序列,以恢复研究区过去约2万年以来的植被变化过程.文中分别给出中国南方18、9和6ka BP前后的植被分带图和各区域植物的分布特征.研究表明:18ka BP前的植被带分布与现在存在着明显的差异,其中西部由西北向东南依次为寒温性针叶林与高寒草甸草原带、温带针阔叶混交林带/暖温带落叶阔叶林带,中东部由北向南依次分布温带针阔叶混交林带、暖温带落叶阔叶林带,以及北亚热带常绿、落叶阔叶混交林带;9ka BP前后的植被面貌发生了明显的变化,除西北部局部地处山地温性针阔叶混交林带外,其他地区由北向南依次分布北亚热带常绿、落叶阔叶混交林亚带,中亚热带典型常绿阔叶林亚带,南亚热带季风常绿阔叶林亚带/热带季雨林和雨林带;6ka BP前后的植被面貌与9ka BP前后的变化不大,但各个植被带的北缘略有北移,反映当时总体气候变得更加温暖.中国南方2万年以来的植被变化,很大程度上受到环境变迁的驱使,其中气候变化为主要影响因素,人类活动的影响在后期变得越来越明显,而在长江下游和三角洲地区,海平面变化对植物的分布同样构成一定的影响. 相似文献
2.
华北平原末次冰盛期以来典型时段古环境格局 总被引：1，自引：0，他引：1
重建典型时段区域气候和植被空间格局变化,是评估未来增温背景下生态环境变化和响应过程的重要基础.文章基于AMS 14C定年技术和孢粉分析,获得了华北平原白洋淀等6个剖面末次冰盛期以来的气候-植被变化历史.结合区内已有孢粉记录,重建了华北平原末次冰盛期和全新世暖期的古环境格局.结果显示,华北平原区域植被变化受气候条件、地貌景观和人类活动等因素共同影响:末次冰盛期,华北平原气候寒冷干旱,南部山地发育针阔混交林和落叶-常绿阔叶林,北部山地生长耐寒针叶林-针阔混交林,森林面积相对较小;平原南部生长中生或湿生草甸,北部发育温带草原-荒漠草原;滨海区陆架大面积出露,生长藜科为主的盐生植物.全新世暖期,华北平原气候温暖湿润,南部山地发育落叶阔叶林或落叶-常绿阔叶混交林,伴生有喜暖亚热带属种,北部山地生长落叶阔叶林,部分喜暖湿植物常有出现,森林面积相对增加;平原腹地草本植物仍占优势,森林面积较小且难以形成地带性森林景观;受海平面上升影响,滨海区原有盐生植被向内陆收缩;此外,这一时期华北平原人类活动范围扩大、农业生产频繁,对区内自然植被产生了一定影响.文章为中国北方古气候数值模拟、区域碳循环评估和未来增温背景下区域生态环境变化预测等提供了基础数据和科学依据. 相似文献
3.
北大兴安岭地区全新世植被演替及气候响应 总被引：1，自引：0，他引：1
《中国科学:地球科学》2016,(6)
通过对大兴安岭北部地区霍拉盆地泥炭剖面和表土样品的花粉分析,重建9100cal a BP以来植被演化历史及其对气候变化的响应过程.结果显示研究区植被经历了从早-中全新世暖温、寒温混合型植被向晚全新世寒温型植被的演变过程.全新世温暖期(9100~6000cal a BP),北大兴安岭寒温带针叶林区气候较现在更为温暖湿润,发育鹅耳枥属、榛属、松属和云杉属为主的暖温型针阔叶混交林,与寒温型落叶松和桦共同组成了特有的混交林地,其植被多样性增加.约6000~5000和3500~2500cal a BP的两次显著的降温事件,导致鹅耳枥属、榛属等喜暖植物类型减少,落叶松属和桦属为主的耐寒植被扩张.2500cal a BP之后,形成落叶松和桦为主的寒温型针阔叶混交林植被景观.全新世温暖期温度增加可能导致东亚夏季风对中国北大兴安岭地区的影响增强,有利于暖温型森林植被发育并增加植物载荷. 相似文献
4.
末次盛冰期以来江西大湖孢粉植被与环境演变 总被引：7，自引：0，他引：7
根据江西定南大湖深346 cm泥炭剖面, 16个14C年龄和76个孢粉样, 重建中国华南南岭山地末次盛冰期以来的植被与气候历史: 大约18330~15630 cal a BP, 景观是落叶阔叶林, 气候温凉偏湿; 15630~11600 cal a BP, 孢粉植被是有常绿阔叶树的落叶阔叶林, 气候温和湿润; 11600~6000 cal a BP, 孢粉植被演替为栲/石栎为建群种的常绿阔叶林, 气候温暖湿润; 而6000 cal a BP以来植被中森林面积减少, 气候温暖偏干, 蕨类植物和草本植物增加, 可能有人类活动的影响. 从孢粉序列中识别到的系列凉干事件, 大致可与北大西洋H1及全新世千年尺度事件对应, 说明低纬地区与高纬地区气候变化密切相关. 与中国高纬地区的季风气候事件对比, 大湖地区气候事件温度、湿度的变幅远低于中国北方内陆地区. 季风气候地域差异性较大. 相似文献
5.
花粉记录的青藏高原中部中全新世以来植被与环境 总被引：2，自引：0，他引：2
唐领余 沈才明 李春海 彭金兰 刘惠 Kam-Biu Liu Carrie Morrill Jonathan T.Overpeck Jonathan E.Cole 杨保 《中国科学D辑》2009,39(5):615-625
青藏高原中部的草甸/草原混合生态群落, 对气候变化非常敏感. 孢粉记录显示草原发育时期, 莎草减少, 区域气候是相对干旱的, 在时间上对应季风相对弱的时期. 依据唐古拉山垭口湖、阿洪错和错那3个淡水湖泊钻孔孢粉分析, 定量重建的温度和降水指标, 探讨该地区8200 cal a BP以来的植被与气候变化. 8200~6500 cal a BP, 尤其是8200~7200 cal a BP, 植被以草甸/草原混合生态群落为主, 显示强季风控制着青藏高原中部; 6000~4900, 4400~3900以及2800~2400 cal a BP时期区域植被以草原植被为主, 应是3次百年尺度的干旱事件; 4900~4400 cal a BP期间植被类型由草原向草甸转变; 6500~5400和 3000~1600 cal a BP出现两次大的变干事件; 数值摸拟估计, 高原中部接近于现今的环境, 最早可能出现在6500 cal a BP, 自3000 cal a BP以后高原中部季风性降水和湿度逐渐减少至现今水平, 可能在700~300 cal a BP出现一次小冰期变冷事件. 相似文献
6.
二万年来长江中下游自然环境变迁及其发展趋向探讨 总被引：1，自引：0，他引：1
20000－15000a.B.P.间气个性候最冷，生长喜冷的针叶林和干旱草原植被。在14780±700a.B.P.出现了最低海面（－154m）；15000－13500a.B.P.,气倏较暖温，涨面上升，生长阔叶混交林；13500－10500a.B.P.，气候有2次温暖和3次较次，在暖期生长针阔叶混交林，较冷期则出现林林草原和草原。最低的温度比现在低5－7℃；一万多年来的冰后期，气候变化分为5个新冰期（包括小冰期）和5个新高温期（包括小气候最宜期0。最高气温比现在主同2－3℃，出现在5000－4000a.B.P.之间；最低温度比现在低3－5℃最高海面在6500－6300a.B.P.，高出现在海面4－5m。在温暖期中生长常绿－落叶阔叶林中亚热带针阔混交林；在较冷期间，生长落叶阔叶林，针叶林或草原草地。在人类影响或自然发展这这结果，未来环境变化有可能向干暖气候和高海面演变，或向干冷气候和海面下降转变，这些变化将对长江中下游带来意外的灾难。 相似文献
7.
云南鹤庆盆地中更新世以来的孢粉记录及其植被与气候变化 总被引：5，自引：0，他引：5
通过对“中国大陆环境钻探计划”首钻——云南鹤庆深钻前155 m约800 ka以来的岩芯进行孢粉研究,探讨了云南鹤庆盆地中更新世以来的植被演替与古气候变迁．研究表明鹤庆盆地周围山地的植被在约800 kaBP至6．98 kaBP之间经历了以松为主的针叶林、山地针阔叶混交林、寒温性针叶林的多次相互演替;从6．98 kaBP开始,植被发生了转折性变化,森林植被迅速退化,以草本为主,此时开始受到人类活动的影响,人类活动表现在砍伐森林和种植农作物等方面.与植被演替相应的古气候可划分为五个大的阶段,包含多次冷暖、干湿旋回． 相似文献
8.
晚冰期以来青海湖沉积物多指标高分辨率的古气候演化 总被引：41，自引：3，他引：41
通过青海湖沉积物孢粉、碳酸盐、有机C, N和有机δ13C等多项指标的综合分析, 建立了青海湖晚冰期以来的高分辨率古气候演化序列. 结果表明, 18.2 cal. ka BP左右为末次冰期盛冰阶进入晚冰期的界限, 自15.4 cal. ka BP起气候开始向暖湿化发展, 7.4 cal. ka BP时达到了暖湿组合的鼎盛期, 4.5 cal. ka BP以后气候又逐步转入冷干. 晚冰期向全新世转换期间气候的冷暖干湿波动十分频繁, 其特征与北大西洋深海沉积、格陵兰冰芯、欧洲地区湖泊沉积以及中国黄土、古里雅冰芯等记录的古气候具有一定的可对比性. 青海湖地区晚冰期以来的古气候演化特征揭示了万年尺度上东亚季风的源驱动力同太阳辐射有关. 相似文献
9.
通过对江汉平原JZ-2010湖相沉积剖面AMS14C年代的精确测定与校正,以及代用指标粒度、磁化率的分析和研究,重建了研究区12.76 cal ka BP以来的环境演变过程:1)12.76-6.70 cal ka BP,区域环境处于偏干的晚冰期向湿润的早全新世发展阶段.2)6.70-4.47 cal ka BP,区域环境湿润,为湿度配置最佳的全新世适宜期,这是大溪文化向屈家岭文化转变时期自然背景.3)4.47-3.67 cal ka BP,区域气候环境偏干,其中经历了明显的4.2 cal ka BP干旱事件.4)3.67-1.22 cal ka BP时期,环境向湿润发展;在2.5 cal ka BP左右水动力条件明显变强,此时正对应于古云梦泽扩张时期.5)1.22 cal ka BP后,研究区处于湖泊面积减小的干旱时期;人类活动带来的影响达到高峰,围湖造田等农业活动也是江汉平原湖群趋于衰退的重要原因之一. 相似文献
10.
赛里木湖孢粉记录的亚洲内陆西风区全新世植被与气候变化 总被引：1，自引：0，他引：1
通过对西风区新疆赛里木湖沉积岩芯的精确定年和孢粉、炭屑分析,重建了该地区全新世以来的植被和气候环境演化历史.结果表明,~9.6cal.kaBP前的早全新世,研究区以荒漠植被为主,A/C比值和第一主成分样品得分所指示的有效湿度明显偏低,第二主成分样品得分所指示的气温回升,气候干旱.9.6~5.5cal.kaBP的中全新世湖区为典型的荒漠草原/草原植被,区域有效湿度明显增加,气温较高,为温暖时期.其中6.5~5.5cal.kaBP期间,研究区植被由荒漠草原/草原迅速转变为荒漠,有效湿度明显降低,同时温度升至最高,可能是一次千年尺度的高温干旱事件.5.5cal.kaBP以来的中-晚全新世,研究区呈现出典型的草原/草甸景观,有效湿度相对较高,温度大幅降低,气候温凉湿润,相对较为适宜.赛里木湖孢粉、炭屑记录的温度和湿度变化与区域其他湖泊记录对比的一致性表明,太阳辐射是造成区域温度变化的主要驱动因素,同时温度变化影响了区域的有效湿度变化.该地区早全新世气候干旱,中-晚全新世气候相对湿润的气候环境演化特征与季风影响区有着明显的差异.早全新世干旱是中纬度西风减弱和上风向蒸发减少的环流背景下局地温度高蒸发强烈的结果. 相似文献
11.
D. M. Pechersky A. A. Lyubushin Z. V. Sharonova 《Izvestiya Physics of the Solid Earth》2010,46(7):613-623
The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The
times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized
by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and
the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between
the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic
world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by
the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle
of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes
in the organic world. 相似文献
12.
Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan. 相似文献
13.
Prof. Dr. W. A. Heiskanen 《Pure and Applied Geophysics》1958,41(1):1-18
Summary The author mentions the aims of the World-wide gravity project he established in the Ohio State University in Columbus, in 1950. He outlines the practical procedure of the gravimetric computations of the undulationsN and the vertical deflection components and and emphasizes that only by the global international cooperation and additional gravity observations at sea carried out during the last decade it has been possible to gather to Columbus the needed gravity material. Since there exist still large gravimetrically unsurveyed areas it is of vital significance to study what gravity anomalies are best to be used for these regions. The given figures concerning the accuracy of theN, and , estimated theoretically and obtained in practice, indicate that in the gravimetrically well surveyed parts of the world like in Europe and the United States we can get gravimetrically on basis of existing gravity material theN-values with accuracy of about 5–10 meters, and and with the accuracy of about 1. The geoid undulationsN are already computed in Columbus for more than 6000 points of the northern hemisphere. The sample maps show the interesting geoid of Europe and vicinity between the latitudes 60° and 30° and longitude 5° W and 30° E, drafted on basis of more than 1000N-values computed at the corners of 1°×1° squares. It is interesting to realize that the geoid undulations in all this area are positive, the extreme values being between 40 and 50 meters. The geophysical significance of the geoid maps of this kind is pointed out. 相似文献
14.
15.
综合APIA、HONOLULU、PAMATAI 3个地磁台三分量的11年周期变化的形态后,可定性地提出该变化源于内场。如内源为核幔边界的电涡流,则其中心点应位于3台之间。 相似文献
16.
V. E. Pavlov T. Yu. Tolmacheva R. V. Veselovskiy A. V. Latyshev A. M. Fetisova I. V. Bigun 《Izvestiya Physics of the Solid Earth》2017,53(5):702-713
Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary. 相似文献
17.
18.
The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data. 相似文献
19.
The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth. 相似文献
20.
Geomagnetism and Aeronomy - The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the... 相似文献