过去200 ka北半球δ18O海温谱及其数值模拟

冰期和间冰期交替循环是第四纪古气候变化的基本特征,大洋底部沉积物中的有孔虫δ＾１８Ｏ记录表明了这种循环具有约１００ｋａ,４１ｋａ和２３ｋａ等几个主主要周期成分,它们均位于Ｍｉｌａｎｋｏｖｉｔｈｃ频率带上,用δ＾１８Ｏ记录恢复的海温谱不仅随纬度变化,而且冷季与暖之间存在着明显的差别,用一个由海、冰、气耦合的二维气候模式出了δ＾１８Ｏ海温谱的主要特征,在一定程度上检验了Ｍｉｌａｎｋｏｖｉｔｃｈ的天文古     

The glacial–interglacial paradox: the relation between the global means of sea level and sea surface temperature

Sea level variability during the Quarternary is simulated using a stochastic climate model, and a sensitivity relation for the change in net oceanic evaporation due to a change in sea surface temperature. In the application of this relation, it is assumed that the greater part of the change in net oceanic evaporation causes changes in the land ice storage, rather than being directly returned to the ocean by rivers. The analysis suggests that the observed sea level changes can be interpreted as due to the transfer of heat to the deep ocean from the surface mixed layer, arising from random radiation perturbations of the same variance as would give rise to the interannual variability of the global temperature series. The paradox is that glacial conditions (increase in ice storage) are favoured by positive (temperate) sea surface temperature anomalies, and interglacial conditions (decrease in ice storage) by negative (temperate) sea surface temperature anomalies. The evolution of both these regimes, which are inherently unstable, appears to be controlled by the deep water formation process, while albedo feedback is of minor importance. Fluvial feedback, (in which as the ice storage increases the fluvial inflow decreases), however, is found to be an important process, and a small sensitivity of river inflow to storage is consistent with forcing by random variability or by astronomical forcing. A simple analytical model incorporating the key processes of oceanic evaporation and fluvial feedback is presented. The analysis points to the importance of an accurate river model for climate system modelling.     

高分辨率地层学与Milankovitch旋回和ENSO事件沉积

围绕地质时间坐标的建立和优化,地层学经历了三次重要革命,形成了三种有代表性的地层学形态：斯坦诺地层学（１６６９年）、史密斯地层学（１８１７年）和高分辨率地层学（１９６９年）。高分辨率地层学的显著特色是划分、对比出的主体地层单元的持续时间必须小于百万年有。十万年级至千年级高分辨率地层划分对比和高分辨率地质时间坐标的建立可望通过对地层记录中Ｍｉｌａｎｋｏｖｉｔｃｈ旋回和ＥＮＳＯ事件沉积的高分辨率地层学     

Amplitude,frequency and drivers of Caspian Sea lake-level variations during the Early Pleistocene and their impact on a protected wave-dominated coastline

The Caspian Sea, the largest isolated lake in the world, witnessed drastic lake-level variations during the Quaternary. This restricted basin appears very sensitive to lake-level variations, due to important variations in regional evaporation, precipitation and runoff. The amplitude, frequency and drivers of these lake-level changes are still poorly documented and understood. Studying geological records of the Caspian Sea might be the key to better comprehend the complexity of these oscillations. The Hajigabul section documents sediment deposited on the northern margin of the Kura Basin, a former embayment of the Caspian Sea. The 2035 m thick, well-exposed section was previously dated by magneto-biostratigraphic techniques and provides an excellent record of Early Pleistocene environmental, lake-level and climate changes. Within this succession, the 1050 m thick Apsheronian regional stage, between ca 2·1 Ma and 0·85 Ma, represents a particular time interval with 20 regressive sequences documented by sedimentary and palaeontological changes. Sequences are regressing from offshore to coastal, lagoonal or terrestrial settings and are bounded by abrupt flooding events. Sediment reveals a low energy, wave-dominated, reflective beach system. Wave baselines delimiting each facies association appear to be located at shallower bathymetries compared to the open ocean. Water depth estimations of the wave baselines allow reconstruction of a lake-level curve, recording oscillations of ca 40 m amplitude. Cyclostratigraphic analyses display lake-level frequency close to 41 kyr, pointing to allogenic forcing, dominated by obliquity cycles and suggesting a direct or indirect link with high-latitude climates and environments. This study provides a detailed lake-level curve for the Early Pleistocene Caspian Sea and constitutes a first step towards a better comprehension of the magnitude, occurrence and forcing mechanisms of Caspian Sea lake-level changes. Facies models developed in this study regarding sedimentary architectures of palaeocoastlines affected by repeated lake-level fluctuations may form good analogues for other (semi-)isolated basins worldwide.     

柴达木盆地东部三湖地区四系米兰柯维奇旋回分析

自然伽马曲线包含丰富的地质信息,能够很好地反映由气候变化引起的地层旋回.本文采用频谱分析对柴达木盆地三湖地区第四系自然伽马测井曲线进行了系统分析.作为频谱分析方法之一的快速傅里叶变换能够将自然伽马曲线从时间（深度）域转换为频率域,然后分析每一个峰值频率的波长及其相互之间的比率关系,寻找那些波长比率与米兰柯维奇周期比率相同或相似的频率,从而捕获高频旋回信息.研究结果表明第四系地层中很好地保存了高频的米兰柯维奇旋回,这样的沉积旋回主要由地球轨道的周期性变化而导致的古气候变化引起的.偏心率周期引起的地层旋回厚度变化范围在92.00~115.00 m之间,黄赤交角引起的地层旋回厚度变化范围在24.55~63.43 m之间,岁差引起的地层旋回厚度变化范围在16.8~26.35 m之间.黄赤交角和岁差是影响该区米兰柯维奇旋回的主要因素,其中岁差的影响最大,而偏心率的影响最小.     

地球气候变化的米兰科维奇理论研究进展

米兰科维奇理论是从全球尺度上研究日射量与地球气候之间关系的天文理论（以下简称为“米氏理论”）。该理论认为,地球轨道偏心率、黄赤交角及岁差等三要素变化引起的到达北半球中高纬度夏季日射量变化是造成冰期—间冰期旋回的根本原因。详细回顾了米氏理论的发展历程,并以南极东方站过去42万年大气和气候变化的历史资料为例,讨论了经典米氏理论中有待研究的若干问题。     

Milankovitch-scale environmental variation in the Banda Sea over the past 820 ka: Fluctuation of the Indonesian Throughflow intensity

We describe the environmental variation in the Banda Sea over the past 820 ka by using the magnetic parameters and oxygen isotope data from the core MD012380. Overall, characteristics of the magnetic parameters show simultaneous variation with marine isotope stage (MIS), especially in the last 420 ka. There are fewer, coarser and more oxidative magnetic minerals in glacial periods, and turn to opposite conditions in interglacial periods. Spectral results clearly present the Milankovitch periods over the last 820 ka, especially the eccentricity period (400-ka and 100-ka). However, the magnetic data shows different pattern before and after 420 ka. Thus, we segmented the time-series data into two periods: MIS 20 to MIS 12 and MIS 11 to MIS 1. During MIS 20 to MIS 12, the spectra of magnetic data show clear periods related to the obliquity (41-ka) and precession (23-ka and 19-ka), while they present only the eccentricity period (100-ka) during MIS 11 to MIS 1. This feature, which splits the late Pleistocene at around 420 ka, could be attributed to the mid-Brunhes event (MBE). In the Banda Sea, main factor controlling the variation of the magnetic minerals is considered as the fluctuation of the Indonesian Throughflow (ITF) intensity due to sea-level change. Thus, the magnetic data show clear 400-ka and 100-ka periods (main MIS cycle). Besides, the eccentricity signals are relatively dominant in the last ～420 ka, implying that the ITF might become more important after the MBE in the Banda Sea.     

Orbitally forced sedimentary rhythms in the stratigraphic record: is there room for tidal forcing?

The imprint of orbital cycles, which result from the varying eccentricity of the Earth’s orbit and changes in the orientation of its axis, have been recognised throughout the Phanerozoic rock record. Variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions. Common oceanographic principles, however, show that the ocean tide also responds to variations in the orbital parameters. The ocean tide has not yet been considered to be a valid, additional transfer mechanism for the orbital variations. In geological studies of Milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations, and the role of long‐term variations of the ocean tide has not yet been appreciated. Variations in the ocean tide, related to changing eccentricity (at present 0·0165, theoretical maximum 0·0728), affect a variety of oceanographic and sedimentary processes. In addition to the widely accepted paradigm of orbitally forced insolation changes, the tidal transfer of orbital signals may explain certain less well‐understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing, organic productivity, and tidal processes in shallow seas and deep water. Variations of the ocean tide in relation to the 18·6 year lunar nodal cycle, which has no insolation counterpart by which they may be obscured, indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide. In analogy with the 18·6 year lunar nodal cycle, orbital variations of the tide on Milankovitch time scales are likely to have affected sedimentary systems in the past.     

藏北雁石坪夏里组高频岩相旋回的驱动机制研究

Walsh频谱分析引用不连续的方波代替傅里叶频谱分析中连续的正弦波和余弦波,由于Walsh函数的不连续性,它广泛应用于地层旋回周期的检测。藏北雁石坪地区中侏罗统夏里组发育一套以砂岩、泥岩为主的高频岩相旋回,在地层颜色上也表现出较好的旋回性。对该组地层岩性和颜色进行Walsh频谱分析对比发现,岩性频谱曲线及颜色频谱曲线的主频周期与米兰科维奇旋回周期之间均具有极好的对应关系,认为海平面的周期性变化是夏里组高频岩相旋回的驱动机制。同时根据岩性旋回频谱和颜色旋回频谱计算得出夏里组的沉积速率约为0．111m／ka,沉积持续时间约为3．689Ma。     

Investigating the preservation of orbital forcing in peritidal carbonates

Metre‐scale cycles in ancient peritidal carbonate facies have long been thought to represent the product of shallow water carbonate accumulation under orbitally controlled sea‐level oscillations. The theory remains somewhat controversial, however, and a contrasting view is that these cycles are the product of intrinsic, and perhaps random, processes. Owing to this debate, it is important to understand the conditions that do, or do not, favour the preservation of orbital forcing, and the precise stratigraphic expression of that forcing. In this work, a one‐dimensional forward model of carbonate accumulation is used to test the ability of orbitally paced sea‐level changes to reconstruct cyclicities and cycle stacking patterns observed in greenhouse peritidal carbonate successions. Importantly, the modelling specifically tests insolation‐based sea‐level curves that probably best reflect the pattern and amplitude of sea‐level change in the absence of large‐scale glacioeustasy. This study found that such sea‐level histories can generate precession and eccentricity water depth/facies cycles in models, as well as eccentricity‐modulated cycles in precession cycle thicknesses (bundles). Nevertheless, preservation of orbital forcing is highly sensitive to carbonate production rates and amplitudes of sea‐level change, and the conditions best suited to preserving orbital cycles in facies/water depth are different to those best suited to preserving eccentricity‐scale bundling. In addition, it can be demonstrated that the preservation of orbital forcing is commonly associated with both stratigraphic incompleteness (missing cycles) and complex cycle thickness distributions (for example, exponential), with corresponding implications for the use of peritidal carbonate successions to build accurate astronomical timescales.