两万年来的中国多年冻土形成演化

利用大量的古多年冻土遗迹和古冰缘现象,并佐以古冰川、孢粉及动物化石等资料,重建了20ka以来中国多年冻土演化进程.结果表明,在末次冰期最盛期(LGM,或末次多年冻土最大期LPMax),中国多年冻土面积达到了5.3×10^6~5.4×10^6km^2(现今中国多年冻土面积的3倍多),而全新世大暖期(HMP,或末次多年冻土最小期LPMin),中国多年冻土面积曾缩减至0.80×10^6~0.85×10^6km^2(约为现今中国多年冻土面积的50%).按照古冻土遗迹的年代及分布等特征,在确定LGM和HMP两个主要时段的冻土格局基础上,将20ka以来中国多年冻土演化进程划分为7个阶段:晚更新世LGM(20000~10800aBP)多年冻土强烈扩展,达到LPMax;早全新世气候剧变期(10800至8500~7000aBP)多年冻土较稳定但相对缩减阶段;中全新世HMP(8500~7000至4000~3000aBP)多年冻土强烈退化阶段,多年冻土缩减到LPMin;晚全新世新冰期(4000~3000至1000aBP)冻土扩展阶段;晚全新世中世纪暖期(1000~500aBP)多年冻土相对退化阶段;晚全新世小冰期(LIA, 500~100aBP)冻土相对扩展阶段,以及近代升温期(近百年来)多年冻土持续退化阶段.本文重建了各时段内古气候、古地理环境以及多年冻土分布范围和其他特征.     

晚冰期以来青海湖沉积物多指标高分辨率的古气候演化

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.     

葫芦洞石笋记录的19．9-17．1ka BP东亚夏季风增强事件

南京葫芦洞石笋（No．H82）高分辨率δ^18 O序列已表明16．5～10．3ka BP时段东亚季风与极地气候在千年尺度事件上存在耦合关系．现根据7个高精度^230Th年龄和573个δ^18 O数据,将这一石笋的高分辨率δ^18 O时间序列延伸至22．1ka BP,从而提供了末次盛冰期10a分辨率的连续东亚季风气候记录．石笋δ^18 O记录表明H1事件内部的次级季风减弱事件与格陵兰寒冷事件在世纪尺度上具有同步性．该记录显示在19．9～17．1ka BP存在显著的东亚夏季风增强事件,其平均夏季风强度相当于BФlling暖期的1／2,夏季风最强时甚至接近于BФlling暖期．这一季风增强事件在北半球海洋和陆地记录中均有不同程度的体现,可能是热带太平洋Super-ENSO响应于岁差周期太阳辐射的结果．     

冲绳海槽中南部18 ka以来的底栖有孔虫与底层水演化

根据冲绳海槽中部E017孔底栖有孔虫的定量分析, 结合浮游有孔虫氧碳同位素、AMS14C测年和前人在冲绳海槽南部的研究资料, 对18 cal. ka BP以来冲绳海槽中南部的底层水团演化进行了初步研究. 结果表明冲绳海槽中南部底栖有孔虫在9.2 cal. ka BP以前的冰期-冰消期以Bulimina aculeata (d’Orbigny), Uvigerina peregrina (Cushman), Hispid Uvigerina和Uvigerina dirupta (Todd)等为主. 在9.2 cal. ka BP以来的冰后期以Epistominella exigua (Brady), Pullenia bulloides (d’Orbigny), Cibicidoides hyalina (Hofker), Sphaeroidina bulloides (d’Orbigny)和Globocassidulina subglobosa (Brady)等为主. 底栖有孔虫堆积速率(BFAR)与生产力定量估算值及底栖有孔虫群落组成等一致反映冲绳海槽中南部冰期-冰消期表层古生产力和有机质通量高于冰后期, 并且在冰期-冰消期表层古生产力由海槽南部向中部逐渐增加, 可能与陆源营养物质的接收量差异有关. 脉冲式有机质输入的指示种E. exigua在9.2 cal. kaBP以后的大量出现可能反映冰后期河流季节性脉冲式注入较冰期-冰消期明显增强, 而且海槽中部接受河流季节性注入的强度可能大于南部. 底层水含氧量与流通状况的典型标志种分布特征显示冲绳海槽中南部冰期-冰消期的底层水流通状况较冰后期弱, 反映冰期西北太平洋中深层水演化没有对冲绳海槽中南部底层水团性质产生影响. 此外, 胶结壳底栖有孔虫的丰度变化和碳酸盐溶解作用表明18 cal. ka BP以来冲绳海槽的碳酸盐溶解作用逐渐增强, 其中9.2 cal. ka BP至今碳酸盐溶解作用急剧增加, 并于最近3 cal. ka BP左右形成现代的浅溶跃面.     

湖北江汉平原JZ-2010剖面沉积物粒度特征与环境演变

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.     

福州盆地全新世沉积物的磁学性质及其对环境变化的响应

福州盆地位于海陆过渡地带,在海陆变迁过程中,沉积物记录了高分辨率的环境信息,是揭示沉积特征对环境变化响应过程及模式的理想区域.本文选择位于福州盆地的FZ5钻孔进行岩石磁学、环境磁学和古地磁学方面的研究,以期阐明该区域沉积物磁学性质对陆源碎屑输入、海平面变化和成岩作用的响应.岩石磁学结果表明钻孔沉积物以低矫顽力的亚铁磁性矿物为主体,但是在不同的环境变化阶段,磁性矿物的类型有较大变化.在9~3 cal. ka BP的海侵过程中,沉积物中以磁铁矿为主体,存在菱铁矿和铁硫化物等还原性矿物.硫化作用使细粒磁铁矿溶解形成胶黄铁矿和黄铁矿,其峰面随碎屑磁性矿物的浓度变化而迁移.但硫化作用没有完全消除磁铁矿携带的特征剩磁和陆源碎屑输入量以及海平面升降对该阶段沉积物磁性的控制.在~3 cal. ka BP以来随着海平面下降、沉积环境向陆相氧化环境转化,虽然早期还原作用仍然存在,但后期氧化作用使磁性矿物向高矫顽力的赤铁矿等矿物转变,氧化作用基本扰乱了磁铁矿携带的剩磁.沉积及其后期成岩作用过程中,发生在约~8.2、~7.7、~7.5、~2.7、~1.5、~0.5 cal. ka BP六次强烈的古氧化界面反映了福州盆地当时异常干旱或湿热的气候事件.     

中国东部山地泥炭高分辨率腐殖化度记录的晚冰期以来气候变化

对中国东部中纬度季风区内的两处山地泥炭——神农架大九湖泥炭和天目山千亩田泥炭腐殖化度进行了研究,并对两剖面的孢粉记录、有机质含量、TOC和Rb／Sr对比分析,结果表明在东亚季风区山间盆地,气候越干冷时泥炭的分解就越强烈,以吸光度表征的腐殖化度就越高;相反,当气候较温暖潮湿时泥炭主要处于还原状态,分解较慢,腐殖化度较低．大九湖剖面的腐殖化度记录了晚冰期（约16．0～11．4cal ka BP）中的新仙女木（YD）（约11．4～12．6cal ka BP）冷干事件、博令．阿勒罗德暖湿期（B．A暖期,约12．6～15．2cal ka BP）、最老仙女木冷干事件（OD,约15．2～16．0cal ka BP）、早全新世的湿润期（约11．4—9．4cal ka BP）、8．2cal ka BP前后的冷干事件和约7．0～4．2cal ka BP之间的全新世最佳适宜期．神农架大九湖和天目山千亩田近5000a以来的泥炭腐殖化度记录有着很好的一致性,表明相近纬度不同经度的山地泥炭对东亚季风降水变化的响应是同步的．近5000a来的气候变化在两个山地泥剖面中几乎同步记录有3大阶段：4．9～3．5cal ka BP,季风降水整体处于高值,但波动剧烈,其中,在约4．2cal ka BP前后,季风降水急剧下降,在3．7cal ka BP前后达到最干旱的峰值后又快速回升：3．5～0．9cal ka BP,季风降水强度整体较弱,但也存在明显的次级干湿波动;0．9cal ka BP以来,吸光度值逐渐降低,表明季风降水增多．与中国东部季风区其他高分辨率沉积记录对比,文中亚高山泥炭记录的约1．6万年以来的气候变化响应了北半球夏季太阳辐射的统一驱动．     

巴丹吉林沙漠全新世的高湖面与泛湖期

巴丹吉林沙漠腹地及东南部湖泊众多,除分布110个常年积水湖泊外,还存在若干季节性湖泊和干涸湖盆.通过对巴丹吉林沙漠湖泊群的实地考察、湖泊遗迹测量及14C和OSL定年,获得了全新世泛湖期存在的地貌学、沉积学和生物遗迹证据,揭示了巴丹吉林沙漠全新世早、中期湖盆面积扩大、区域气候相对湿润的特点.测年结果表明,巴丹吉林沙漠泛湖期开始于10cal ka BP,此前为泥炭发育期或湖沼期(11~10cal ka BP),大致在8.6~6.6cal ka BP,湖泊群达到全新世最大高湖面,并于晚全新世(约3.5cal ka至今)普遍出现退缩乃至干涸.根据植物钙质根管的形成时代及其所揭示的降水量阈值研究,巴丹吉林沙漠东南部在7.7~5.3cal ka BP期间古降水量可能达到200mm a~(-1).水量平衡计算表明,百年至千年尺度相对暖湿的区域气候条件,特别是南部和东南部深层地下水来水量增多,是巴丹吉林沙漠全新世湖泊群维持和史前文化发展的关键因素.     

晚第四纪对马暖流的演化和变动: 浮游有孔虫和氧碳同位素证据

在对取自对马暖流影响区的CSH1和黑潮主流轴影响下的DGKS9603孔沉积物中的浮游有孔虫种群以及混合层种Globigerinoides ruber和温跃层种Neogloboquadrina dutertrei的δ¹⁸O, d¹³C记录的对比分析基础上, 探讨了晚第四纪对马暖流的演化和变动. 结果表明在40~24 cal ka BP的低海平面时期对马暖流消失, 然而黑潮仍然存在于冲绳海槽内部, 黑潮水体在海槽北部的爬升引起显著的上升流, 同时低海平面也使得陆源冲淡水对于海槽北部的影响加强; 冲淡水的影响在末次冰期最盛期(LGM)期间达到顶峰, 而最低海平面和黑潮的减弱使得LGM期间上升流明显减弱; 现代对马暖流的发育始于16 cal ka BP左右; 冰消期中黑潮对于海槽区影响的加强在中部和北部是同步发生的, 伴随其发育过程, 黑潮水体逐渐成为对马暖流主要的水体来源; 而现代对马暖流的最终形成是在8.5 cal ka BP左右, 此后这种环流格局相对稳定, 从水体组成上而言现代对马暖流水体主要来源于黑潮主干; 距今3.0 cal ka BP左右, 可能是在冬季风强化和黑潮减弱的背景下, 对马暖流流径发生了一次偏转, 导致冷水团影响加强.     

末次盛冰期以来南海南部天然气水合物储库变化及其对环境的影响

末次盛冰期以来南海南部海平面及海洋底水温度均发生了很大的变化. 为了研究南海南部天然气水合物稳定带厚度在这个过程中的变化情况及其对环境的影响,我们利用相关的计算公式,并编制了计算稳定带厚度的程序,在南海南部的南沙海槽、曾母盆地、巴拉望盆地和苏禄海等四个重点海域选取了35个点进行末次盛冰期及目前稳定带厚度的计算. 计算结果表明,南海南部末次盛冰期和目前的天然气水合物稳定带厚度分别为262m和233m;甲烷资源量分别为269×1013m3和239×1013m3;水合物资源量分别为164×1011m3和146×1011m3. 这说明自末次盛冰期以来,南海南部稳定带厚度平均减薄了29m,平均减薄百分比为12%,同时释放了大约30×1012m3的甲烷,这些甲烷对环境产生了较大影响,对末次冰期的结束起了较大作用.     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

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.     

On the gravimetric undulations of the geoid and the deflections of the vertical

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.     

On the maintenance of the axisymmetric part of the flow in the atmosphere

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.     

太平洋中部地磁台11年周期变化的研究

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。     

Comparison Between the Nutations of the Planet Mars and the Nutations of the Earth

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.     

Magnetic stratigraphy of the Ordovician in the lower reach of the Kotuy River: the age of the Bysy-Yuryakh stratum and the rate of geomagnetic reversals on the eve of the superchron

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.     

On the variation in the geomagnetic dipole over the geological history of the Earth

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.     

Structure of the poleward wall of the trough and the inclination of the geomagnetic field above the EISCAT radar

A special high-resolution routine of the EISCAT radar has been used to investigate the structure and development of the poleward wall of a deep trough in electron density. The feature was tracked by the radar during a 7-hour period under very quiet geomagnetic conditions. The field-aligned nature of the structure enabled an estimate to be made of the inclination of the geomagnetic field above EISCAT that was in good agreement with the current model. Observations of narrow field-aligned enhancements in electron temperature demonstrated that the wall of this trough is a dynamic feature, reforming regularly as the electron density responds on a time scale of tens of minutes to energy input from soft-particle precipitation.