Combined obliquity and precession pacing of late Pleistocene deglaciations

Milankovitch proposed that Earth resides in an interglacial state when its spin axis both tilts to a high obliquity and precesses to align the Northern Hemisphere summer with Earth's nearest approach to the Sun. This general concept has been elaborated into hypotheses that precession, obliquity or combinations of both could pace deglaciations during the late Pleistocene. Earlier tests have shown that obliquity paces the late Pleistocene glacial cycles but have been inconclusive with regard to precession, whose shorter period of about 20,000 years makes phasing more sensitive to timing errors. No quantitative test has provided firm evidence for a dual effect. Here I show that both obliquity and precession pace late Pleistocene glacial cycles. Deficiencies in time control that have long stymied efforts to establish orbital effects on deglaciation are overcome using a new statistical test that focuses on maxima in orbital forcing. The results are fully consistent with Milankovitch's proposal but also admit the possibility that long Southern Hemisphere summers contribute to deglaciation.     

Intensified deep Pacific inflow and ventilation in Pleistocene glacial times

The production of cold, deep waters in the Southern Ocean is an important factor in the Earth's heat budget. The supply of deep water to the Pacific Ocean is presently dominated by a single source, the deep western boundary current east of New Zealand. Here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep-water properties and speed changes during the Pleistocene epoch. In physical and isotope proxies we find evidence for intensified deep Pacific Ocean inflow and ventilation during the glacial periods of the past 1.2 million years. The changes in throughflow may be directly related to an increased production of Antarctic Bottom Water during glacial times. Possible causes for such an increased bottom-water production include increasing wind strengths in the Southern Ocean or an increase in annual sea-ice formation, leaving dense water after brine rejection and thereby enhancing deep convection. We infer also that the global thermohaline circulation was perturbed significantly during the mid-Pleistocene climate transition between 0.86 and 0.45 million years ago.     

Early onset and tropical forcing of 100,000-year Pleistocene glacial cycles

Between 1.5 and 0.6 Myr ago, the period of the Earth's glacial cycles changed from 41 kyr, the period of the Earth's obliquity cycles, to 100 kyr, the period of the Earth's orbital eccentricity, which has a much smaller effect on global insolation. The timing of this transition and its causes pose one of the most perplexing problems in palaeoclimate research. Here we use complex demodulation to examine the phase evolution of precession and semiprecession cycles--the latter of which are phase-coupled to both precession and eccentricity--in the tropical and extratropical Atlantic Ocean. We find that about 1.5 Myr ago, tropical semiprecession cycles (with periods of about 11.5 kyr) started to propagate to higher latitudes, coincident with a growing amplitude envelope of the 100-kyr cycles. Evidence from numerical models suggests that cycles of about 10 kyr in length may be required to explain the high amplitude of the 100-kyr cycles. Combining our results with consideration of a modern analogue, we conclude that increased heat flow across the equator or from the tropics to higher latitudes around 1.5 Myr ago strengthened the semiprecession cycle in the Northern Hemisphere, and triggered the transition to sustained 100-kyr glacial cycles.     

A late Eemian aridity pulse in central Europe during the last glacial inception

Investigating the processes that led to the end of the last interglacial period is relevant for understanding how our ongoing interglacial will end, which has been a matter of much debate (see, for example, refs 1, 2). A recent ice core from Greenland demonstrates climate cooling from 122,000 years ago driven by orbitally controlled insolation, with glacial inception at 118,000 years ago. Here we present an annually resolved, layer-counted record of varve thickness, quartz grain size and pollen assemblages from a maar lake in the Eifel (Germany), which documents a late Eemian aridity pulse lasting 468 years with dust storms, aridity, bushfire and a decline of thermophilous trees at the time of glacial inception. We interpret the decrease in both precipitation and temperature as an indication of a close link of this extreme climate event to a sudden southward shift of the position of the North Atlantic drift, the ocean current that brings warm surface waters to the northern European region. The late Eemian aridity pulse occurred at a 65 degrees N July insolation of 416 W m(-2), close to today's value of 428 W m(-2) (ref. 9), and may therefore be relevant for the interpretation of present-day climate variability.     

Climatic instability recorded by the mollusk assemblages from the late glacial loess deposits in China

The loess-paleosol sequence in China records abundant and valuable information on the global and regional climate changes. Biological record from the loess sequence is the most direct evidence on variation in pattern of paleo-atmospheric circulation and changes in winter and summer monsoon. A new record of climatic instability, which occurred in the Loess Plateau during the late glacial period, is presented. Through the study of terrestrial mollusks from three loess sequences, the authors intend to characterize the biological response process to rapid climate change and to learn the mechanisms driving the instable climate changes and the possible linkage in different regions. The result shows the striking consistent variability in the ratio records of three mollusk sequences of the late glacial, indicating apparent rapid climate fluctuations. Correlation of our three mollusk records with the oxygen isotopic records from Greenland ice cores and foraminifera1 records from the Northeast Pacific Ocean reveals similar instability climate during the late glacial period, which provides us a new thought probing the climate instability observed in the North Atlantic, the North Pacific and the Loess Plateau. The low-level atmospheric circulation in the Northern Hemisphere may be one possible way to link the unstable climate patterns observed in the above three regions.     

Astronomical pacing of late Palaeocene to early Eocene global warming events

At the boundary between the Palaeocene and Eocene epochs, about 55 million years ago, the Earth experienced a strong global warming event, the Palaeocene-Eocene thermal maximum. The leading hypothesis to explain the extreme greenhouse conditions prevalent during this period is the dissociation of 1,400 to 2,800 gigatonnes of methane from ocean clathrates, resulting in a large negative carbon isotope excursion and severe carbonate dissolution in marine sediments. Possible triggering mechanisms for this event include crossing a threshold temperature as the Earth warmed gradually, comet impact, explosive volcanism or ocean current reorganization and erosion at continental slopes, whereas orbital forcing has been excluded. Here we report a distinct carbonate-poor red clay layer in deep-sea cores from Walvis ridge, which we term the Elmo horizon. Using orbital tuning, we estimate deposition of the Elmo horizon at about 2 million years after the Palaeocene-Eocene thermal maximum. The Elmo horizon has similar geochemical and biotic characteristics as the Palaeocene-Eocene thermal maximum, but of smaller magnitude. It is coincident with carbon isotope depletion events in other ocean basins, suggesting that it represents a second global thermal maximum. We show that both events correspond to maxima in the approximately 405-kyr and approximately 100-kyr eccentricity cycles that post-date prolonged minima in the 2.25-Myr eccentricity cycle, implying that they are indeed astronomically paced.     

山西太原田庄断裂晚更新世活动的证据

田庄断裂为北东东向的斜穿太原盆地北部的隐伏活动断裂,通过在马练营路附近实施横跨田庄断裂的联合钻孔勘探,发现地层呈现出3段明显的河-湖-沼泽相沉积旋回特征:80～60 m段,沉积环境逐步趋于频繁,沉积相为湖泊→沼泽; 60～30 m段,沉积环境两次经由频繁趋于稳定再到频繁,沉积相为河流→沼泽→河流→湖泊→沼泽→河流; 30～0 m段,沉积环境逐步趋于稳定,沉积相为沼泽→湖泊→沼泽.地层岩性表现出:青灰色粉质黏土在从南至北方向上呈现出深度变深,终止深度变浅,在钻孔ZK3←→ZK4←→ZK7间均出现量级的转折变化;黄褐、褐黄色粉砂、细砂在从南至北方向上整体出现深度在20～30 m,浮动不大,终止深度变深.田庄断裂断错地层主要有3套,均为晚更新世地层,未穿透上更新统,由此判定目标断裂为晚更新世活动断层,从上到下,断错地层错距逐渐加大,依次为0.4 m、3.5 m、7.2 m,错距在钻孔所揭露深度内有两次3 m左右的同震位移,可以判断在该识别层内发生两次主错动事件,这为分析田庄断裂的地震危险性提供了可靠的地质证据.     

湿式气柜倾斜度的定位测量

简述了低压气柜过度倾斜对其运行的影响，介绍了低压气柜倾斜度的测量原理、检测方法，根据检测结果对气柜运行的安全性进行了评价。     

Evidence of two temperate episodes in late Pleistocene deposits at Marsworth, UK

In the British Quaternary, two post-Cromerian interglacials, the Hoxnian and the Ipswichian, are recognized. Evidence of additional interglacials in this interval is widely accepted in the oceanic record of Quaternary events, and the possibility that at least one additional interglacial of this age is represented in Britain has been discussed. However, in the absence of datable interglacial deposits which are seen to overlie one another, the issue has remained controversial. We describe here deposits at Marsworth, UK (Fig. 1) where there is evidence of two temperate episodes, and of intervening periglacial conditions. Stratigraphical superposition is established beyond any reasonable doubt. The later deposit relates to the temperate woodland stage of the Ipswichian Interglacial. Dating of the earlier temperate material by the 230Th/234U disequilibrium method indicates an interglacial episode not previously established in the British Quaternary.     

天津蓟县晚更新世象化石分布与地貌特征

描述和对比了天津蓟县晚更新世地层发现的纳玛象、诺氏象第二门齿及第三臼齿化石,由于4处化石发现地均在天津蓟县，相互之间距离很近，且都在山前丘陵和平原区内，故具有一定的地域特点，小范围内发现古菱齿象属的2个种，在北方具有一定代表性，说明在晚更新世温暖期中，蓟县由于特殊地貌所形成的森林茂盛、淡水充沛、气候温和的特点，更适合象及其他如鹿、牛、羊等大型哺乳动物的生长和繁殖．     

Structural deformation and fault activity of the Tan-Lu Fault zone in the Bohai Sea since the late Pleistocene

The Tan-Lu Fault zone (TLFZ) is a significant fractural zone in eastern China and also a seismicity belt in North China. Based on total 4000-km-long shallow penetrated single seismic data with high-resolution, structural deformation and fault activity of the TLFZ in the Bohai Sea since the late Pleistocene are discussed in detail. The results show that the TLFZ with a discontinuous distribution and a general NNE-trending consists of 14 active subfaults with an NNE or NE strike in the Bohai Sea. Seismic data reveal that de-formation zones along the subfaults in the central Bohai Sea and the Laizhou Bay are wider and more complex than those in the Liaodong Gulf. Related folds and lots of secondary normal faults which are characterized by nearly vertical fault planes and a same or reverse dip construct the fractural zone in the Laizhou Bay and the central Bohai Sea. Usually, micro symmetrical grabens develop on the top of anticlines. In the Liaodong Gulf, subfault fractural zones usually consist of secondary normal faults with the same inclination or opposite inclination. Ages of seismic sequences and cutting relation between subfaults and seismic sequences suggest that the latest faulting age of the TLFZ is the end of the late Pleistocene in the Liaodong Gulf and the early Holocene in the Laizhou Bay and the central Bohai Sea. There is a good match between distribution of earthquakes and that of the subfaults in the Laizhou Bay and the central Bohai. Statistical result shows that total vertical offset of the TLFZ since the late Pleistocene ranges from 6 to 11 m. On the basis of offsets of the subfaults, the vertical slip rate is calculated and results show that average vertical slip rates in the central Bohai Sea are larger than those in the Liaodong Gulf and the Laizhou Bay. Slip rates more than 0.06 mm/a during 23–10 ka B.P. and 85–65 ka B.P. are larger than those in other stages. The TLFZ was mainly dominated by tensional normal component since the late Pleistocene. Synthesizing shallow deformation, activity and distribution of earthquakes, the TLFZ in the Bohai Sea can be divided into three segments: the Laizhou-Bay segment, the Bozhong segment, and the Liaodong-Gulf segment.     

Evidence of fire use of late Pleistocene humans from the Huanglong Cave, Hubei Province, China

Since 2004, three excavations have been carried out at a late Pleistocene human fossil site of Huanglong Cave in Yunxi County, Hubei Province of China, which unearthed seven human teeth, dozens of stone tools, mammal fossils and other evidence indicating human activities. During the third excavation in 2006, in the same layer as the human teeth, we found some patches of black materials embedded in the deposit. We doubted that this black deposit layer is the remains of burning or even human use of fire at the cave. To further explore the possibility of human fire use at the Huanglong Cave, we examined samples directly taken from the black deposit layer and compared them with samples taken from several places in the cave using three methods: micromorphology, element content determination and deposit temperature analysis. Our results indicate that the contents of carbon element in the black deposit reach 64.59%―73.29%. In contrast, contents of carbon element of the comparative samples from other parts in the cave are only 5.82%―9.49%. The micromorphology analysis of the black deposit samples reveals a plant structure like axial parenchyma, fibrocyte, uniseriate ray and vessel. High-temperature magnetic susceptibility measurements suggest that the stratum possibly underwent a high temperature in the nature. Based on these lab analyses, we are sure that the black layer in the Huanglong Cave is the remains of fire and combustion did occur in the cave 100000 years ago. Taking other evidence of human activities found in the Huanglong Cave into consideration, we believe that the evidence of fire from the Huanglong Cave was caused by the human activities of controlled use of fire.     

临河凹陷QK3钻孔220 ka以来的沉积环境演变记录

临河凹陷是河套盆地的一部分,黄河由西向东流经,其内发育了巨厚的沉积地层,是第四纪环境演变的理想场所。通过分析临河凹陷中QK3钻孔地层的粒度特征,结合年代地层重建了研究区中更新世晚期以来的沉积环境演变过程:189.9 ka.BP～220.26 ka.BP表现为滨湖相沉积;117.47 ka.BP～189.9 ka.BP表现为河流边滩沉积;117.47 ka.BP～189.9 ka.BP表现为河流边滩沉积;38.5 ka.BP～117.47 ka.BP表现为河流边滩和河漫湖泊的交替沉积环境;13.49 ka.BP～38.5 ka.BP表现为河流边滩相沉积环境;13.49 ka.BP以来表现为河漫湖泊相沉积环境。     

柔性透水促淤浮帘倾斜角度实验研究

通过室内定床水槽实验研究一种新型的岸滩促淤装置--柔性透水浮帘的水力性能.在系统的观测数据基础上重点分析了浮帘在水流作用下的倾斜角度的影响因素和变化规律.实验分析表明,浮帘倾角由来流的弗劳德数、浮帘密度、浮帘相对高度、浮帘过沙窗口的相对大小和相对位置高度5个因素决定,并随这些因素呈现明显的规律性变化.根据实验结果拟合出浮帘倾角和这些因素之间的关系式,并在数学和理论上证明了该式具有合理性和普遍适用性.     

关中东部渭河右岸晚更新世以来黄土的粒度特征与物源分析

为了探究关中东部渭河右岸晚更新世以来黄土在粒度、厚度、湿陷性等方面与渭北及关中其它地区存在显著差异的原因,在研究区从东向西选择2条近南北向断面共6个黄土剖面,对黄土地层进行野外实际观察,并采集样品380件进行室内粒度分析。研究结果显示从东向西、由北向南,黄土地层厚度逐渐变小,黄土粒度组成上砂粒含量减少,粘粒含量增加。说明区域黄土是由近源粉砂（东偏北风搬运）与远源粉尘（西北风搬运）共同堆积的产物。     

Climatic changes from the late Pliocene to middle Pleistocene in and around central Japan reconstructed from plant macrofossil assemblages

We used composition of plant macrofossil assemblages obtained mainly from the Osaka Group in central Japan to reconstruct the palaeoclimate between the late Pliocene (about 3.3 m.y. B.P.) and the middle Pleistocene (about 0.4 m.y. B.P.). The warmest climate of the period was before 3.0 m.y. B.P. Cool-temperate elements increased and subtropical elements decreased between 3 m.y. B.P. and 2.7 m.y. B.P., indicating the first climatic deterioration. The first occurrence of subarctic elements characterizes the Plio-Pleistocene boundary as a severe cold stage. After 1.1 m.y. B.P., climatic fluctuation occurred at less than 100,000 year intervals. A severe cold stage occurred just after the Jaramillo event (about 0.8 m.y. B.P.). The warmest stage in the middle Pleistocene occurred at about 0.5 m.y. B.P. With it evergreen broad-leaved forest expanded into central Japan. The climatic curves reconstructed from plant macrofossils parallel the climatic changes reconstructed from loess - paleosol stratigraphy in Central China, radiolarian faunal stratigraphy in the north Pacific deep sea drilling core, oxygen-isotope data in the North Pacific, and pollen spectra in western Europe.     

机载悬挂发射倾角控制系统的建模与仿真

该文以采用高压氮气作为工作能源的多级活塞式机载悬挂弹射装置为研究对象,针对悬挂物质心偏离两弹射筒对称轴线时,在弹射过程中出现倾斜的问题,提出了弹射倾角控制系统的设计方案,建立了该控制系统的数学模型和线性化模型,引入PID控制和模糊自适应整定PID控制算法,并运用MATLAB中的Simulink模块对该系统进行了仿真分析,验证了方案的可行性.文中建立的控制系统理论模型、控制算法及仿真结果对该系统的实际开发具有重要的参考意义.