TESTING LAKE SEDIMENT AND DENDROGEOMORPHIC PROXIES FOR LITTLE ICE AGE ENVIRONMENTAL CHANGE IN THE UPPER FRASER RIVER AREA,BRITISH COLUMBIA,CANADA

This study assesses Little Ice Age (LIA) lake sediment morphological and geochemical records and moraine chronologies in the upper Fraser River watershed, British Columbia, Canada, to resolve differences in paleoenvironmental interpretation and to clarify sediment production and sediment delivery processes within alpine geomorphic systems. Moose Lake (13.9 km²), situated at 1032 m a.s.l., contains a partially varved record indicating variable rates of accumulation during the last millennium that, in general, coincide with previously documented LIA glacial advances in the region and locally. Dendrochronological assessment of forefield surfaces in the headwaters of the catchment (Reef Icefield) shows that periods of moraine construction occurred just prior to ad 1770, ad 1839 and ad 1883, and some time before ad 1570. Taken collectively, increases in varve thickness within eight Moose Lake sediment cores coincide with documented glacier advances over the twelfth through fourteenth centuries, the eighteenth century, and nineteenth through twentieth centuries. Glacial activity during the sixteenth century is also indicated. While varve thickness variations in proximal and distal sediments clearly reflect glacial activity upstream of Moose Lake, the intermediate varve record is relatively insensitive to these decadal and longer‐term catchment processes. Variations in Ca and related elements derived from glaciated carbonate terrain within the Moose River sub‐catchment (including Reef Icefield) indicate gradually increasing delivery from these sources from the twelfth through twentieth centuries even where the varve thickness record is unresponsive. Elevated carbonate concentrations confirm glacial activity c. ad 1200, ad 1500, ad 1750, and ad 1900.     

Signature of long supercycles in the Pleistocene history of Asian limnic systems

The analysis of sediment chemistry and biota in drill cores from Lake Khubsugul in Mongolia (KDP-01) and Lake Baikal in Siberia (BDP-96/1), two great Eurasian freshwater lakes, detected prominent climate and biological events at 460–420 and 670 kyrs BP in addition to the orbital cycles of precession, tilt and eccentricity. The revealed long-term events were associated with notable changes in biodiversity and geography/landscapes, mainly in water budgets and weathering patterns. The span between 460–420 and 670 kyrs BP was the time when the climate and geographic conditions differed from those before and after these events. The corresponding 33–24 m (670–460 kyr) interval of the Khubsugul core lacked the usual signature of the Milankovitch glacial/interglacial cycles. Events of approximately these ages were found in some other continental ecosystems and in oceanic δ¹³C records. The two events may mark the phases of a 300–500-kyr long supercycle (or megastadial) in the evolution of continental ecosystems. Among other causes (e.g., regional tectonic events), this periodicity, being globally correlated, may be associated with the 400-kyr cycle of the Earth’s orbital eccentricity.     

冰芯与其它记录所揭示的中国全新世大暖期变化特征

冰芯,孢粉,黄土,湖泊和海平面变化记录揭示出,在全新世时,我国曾发生过多次气候冷暖波动事件,其中最重在的事件是全新世大暖期,由于青藏高原在存在。造成了中亚地区大气环流的改变。形成了中国大陆复杂的气候条件和独特的季风气候,从而导致全国各地大暖期在起讫时间,变化幅度和持续时间上都存在着较大的差异。中国西部高海拔地区大暖期起讫时间较早,持续时间较短。变化幅度较大;反之,在中国东部,大暖期起讫时间较晚,持续时间较长。变化幅度较小,反映出西部高海拔区域对气候变化的响应度和敏感度都比东部低海拔区域强,此外,不同区域的冰芯记录也有差异。古里雅冰芯记录反映了全球气候变化的趋势,而敦德冰芯记录则与我国季风气候变化的趋势比较接近。     

大别山中生代构造演化:来自盆地充填记录的启示

通过对大别山周缘盆地的对比分析,研究了大别山中生代构造演化格局。盆地充填序列分析表明,尽管中生代大别山南、北盆山耦合关系不同,但构造体制均经历了前白垩纪挠曲向白垩纪伸展的转化;砂岩物源再造反映中生代南大别山源区剥露尚未大规模触及岩浆弧“根”,剥露深度浅于北大别单元。大别山邻区晚中生代巨厚磨拉石是陆内造山强烈阶段的沉积记录,它们的产出及相关的造山带隆升与该区超高压变质岩快速折返没有直接关系。进一步讨论了恢复大别山物源结构、建立盆地类磨拉石精细地层年代学格架等在造山带构造研究中的重要性及其现存的关键问题。     

3D configuration of Mygdonian basin and preliminary estimate of its site response

Euroseistest is currently the longest running test site in the world. It was originally defined as the 2D cross-section of the Mygdonian basin going from Profitis to Stivos villages. In this paper, we present the first results of the effort to extend the idea of test site to a larger portion of the whole sedimentary structure, i.e. the extension of the idea of Euroseistest from a 2D to a 3D structure. To this end we have compiled available geological and geotechnical information. We have analyzed microtremor and earthquake data recorded seven years ago, that had not been thoroughly exploited. We present the results of the analysis of H/V spectral ratios from microtremors recorded at 195 sites, and from earthquake records at 14 stations. The results are validated through comparison with the well studied 2D cross-section. In addition to this, the geometry of the edges of the basin has been deduced from electrical tomographies. The synthesis of all these data allowed us to propose reliable map of dominant frequencies throughout the basin, a good constrain on the geometry of the basin at the edges, and shear-wave velocity profiles at some points. Our results indicate that average shear-wave velocity is not constant throughout, and thus the dominant frequency map is not a faithful image of the geometry of the basin. We have also obtained a reliable estimate of the site response throughout the basin. The results have been used to plan an additional measurement campaign, and are currently used to compute site response using a 3D seismic modelling code. We expect that the usefulness of Euroseistest to understand site effects in 3D geological structures will be as large as it has been in its 2D phase.     

A stratigraphic network across the Subtropical Front in the central South Atlantic: Multi-parameter correlation of magnetic susceptibility, density, X-ray fluorescence and δO records

Computer aided multi-parameter signal correlation is used to develop a common high-precision age model for eight gravity cores from the subtropical and subantarctic South Atlantic. Since correlations between all pairs of multi-parameter sequences are used, and correlation errors between core pairs (A, B) and (B, C) are controlled by comparison with (A, C), the resulting age model is called a stratigraphic network. Precise inter-core correlation is achieved using high-resolution records of magnetic susceptibility κ, wet bulk density ρ and X-ray fluorescence scans of elemental composition. Additional δ¹⁸O records are available for two cores. The data indicate nearly undisturbed sediment series and the absence of significant hiatuses or turbidites. After establishing a high-precision common depth scale by synchronously correlating four densely measured parameters (Fe, Ca, κ, ρ), the final age model is obtained by simultaneously fitting the aligned δ¹⁸O and κ records of the stratigraphic network to orbitally tuned oxygen isotope [J. Imbrie, J. D. Hays, D. G. Martinson, A. McIntyre, A. C. Mix, J. J. Morley, N. G. Pisias, W. L. Prell, N. J. Shackleton, The orbital theory of Pleistocene climate: support from a revised chronology of the marine δ¹⁸O record, in: A. Berger, J. Imbrie, J. Hays, G. Kukla, B. Saltzman (Eds.), Milankovitch and Climate: Understanding the Response to Orbital Forcing, Reidel Publishing, Dordrecht, 1984, pp. 269-305; D. Martinson, N. Pisias, J. Hays, J. Imbrie, T. C. Moore Jr., N. Shackleton, Age dating and the orbital theory of the Ice Ages: development of a high-resolution 0 to 300.000-Year chronostratigraphy, Quat. Res. 27 (1987) 1-29.] or susceptibility stacks [T. von Dobeneck, F.Schmieder, Using rock magnetic proxy records for orbital tuning and extended time series analyses into the super-and sub-Milankovitch Bands, in: G. Fischer, G. Wefer (Eds.), Use of proxies in paleoceanography: Examples from the South Atlantic, Springer-Verlag, Berlin (1999), pp. 601-633.]. Besides the detection and elimination of errors in single records, the stratigraphic network approach allows to check the intrinsic consistency of the final result by comparing it to the outcome of more restricted alignment procedures. The final South Atlantic stratigraphic network covers the last 400 kyr south and the last 1200 kyr north of the Subtropical Front (STF) and provides a highly precise age model across the STF representing extremely different sedimentary regimes. This allows to detect temporal shifts of the STF by mapping δMn / Fe. It turns out that the apparent STF movements by about 200 km are not directly related to marine oxygen isotope stages.     

青藏高原沱沱河至昆仑河地区晚更新世以来孢粉记录的古环境信息

根据对青藏高原沱沱河流域的雅西错湖湖相沉积、西金鸟兰湖岸边的湖相沉积和昆仑河河流相沉积记录的晚更新世以来的孢粉资料的对比分析，该地区2种标志性花粉蒿属（Artemisia）、藜科（Chenopodiaceae）的百分含量表现出明显的负相关性，从南向北、从老到新，孢粉的种类、乔木花粉的数量逐渐减少，禾本科（Gramineae）花粉百分含量逐渐降低，蕨类孢子数量少；在研究区南部晚更新世早期出现了以白刺属（Nitraria）为代表的干旱灌丛草原植被，在研究区3-1万年之间出现了以蒿属、禾本科为代表的干偏湿的草原植被；总体上，根据晚更新世的孢粉恢复的古环境，南部地区比北部地区偏湿。这一特征对恢复青藏高原晚更新世的古环境具有重要的参考意义。     

Nonlinearity in the response of soils in the 1995 Kobe earthquake in vertical components of records

Strong motion records provided by seismic vertical arrays allow estimation of stress–strain relations in soils at depths from the surface to the location of the deepest device. As an example, time-dependent nonlinear soil behavior was estimated in vertical components of records obtained in the epicentral area of the 1995 Kobe earthquake. Degradation of the rigidity of soils in the strong motion was observed. The constructed nonlinear models of the soil behavior were used for estimating the nonlinear parts in the ground response by the nonlinear system identification technique. Nonlinear parts in the ground response were found to be as high as 50% at 2 km from the fault and 10% at 6–15 km from the fault plane. Odd types of nonlinearity, such as cubic, the fifth, seventh, etc. order, were found to be typical for soils, whereas, nonlinearities of even types are usually weak, but increase in liquefied soils.     

青藏高原冰芯定年方法回顾及新技术展望

冰芯高分辨率高保真地记录了过去不同时间尺度气候环境变化历史,而冰芯精确定年是重建过去气候环境演化的先决条件。通过回顾青藏高原冰芯定年的常用方法,提出了目前冰芯定年仍存在的挑战和机遇。通常的冰芯定年方法包括基于冰芯季节变化信号的数年层方法、放射性标志层定年、冰川流动模型、基于其他已知时间序列的对比定年,以及放射性同位素定年。最可靠的方法是数年层的方法,但受到冰川中下部年层逐渐减薄的制约,冰川流动模型主要应用于冰芯中下部定年,但存在不确定性较大而且难以验证的难题。未来冰芯学科发展对冰芯定年提出了更高要求,随着测量技术与手段的突破,新的方法与技术开始在极地冰芯与高山冰芯定年研究中展示了广泛的应用前景。冰芯连续测量技术（如冰芯同位素连续测量技术、激光剥蚀等离子体质谱技术）大幅度提高了冰芯测量结果的时间精度,有可能把数年层的定年方法延推到冰芯底部;基于“原子阱痕量分析”（Atom Trap Trace Analysis,ATTA）的惰性气体（⁸⁵Kr、⁸¹Kr、³⁹Ar）放射性测年技术是一项革命性的技术,由于惰性气体在大气中的稳定性与均匀性使其在不同时间尺度冰川冰的绝对定年中发挥出优势。低浓度的可溶性有机碳的¹⁴C定年也从实验室探索阶段开始转入试用阶段,而且用冰量低,有望解决冰芯中碳含量低,定年困难的窘迫状况。此外,人类活动影响之前处于自然背景下的冰芯³H低本底测量技术结合数据处理方法,有望恢复过去100~200年与太阳活动周期相关的信号,将补充放射性标志层只有近代结果的不足。这些新的技术与方法在冰芯定年中的应用有望进一步推动中低纬度高山冰芯研究。     

2014年9月大气环流和天气分析

2014年9月环流特征如下：北半球高纬地区极涡为单极型,中高纬地区呈6波型分布,西北太平洋副热带高压与常年同期相当,9月全国平均降水量为80.7 mm,比常年同期（65.3 mm）偏多23.6%;全国9月平均气温为17.1℃,较常年同期（16.6℃）偏高0.5℃。 月内共有6次强降水过程,四川盆地东北部、陕西中南部、河南等地共有113站发生极端连续降水日数事件,陕西中南部、山西西南部、河南西部和四川东北部等地共有96站发生极端连续降水量事件。月内,台风海鸥和凤凰先后登陆我国;华西地区、黄淮大部、华北西南部等地出现持续降雨过程;甘肃、陕西及河南等地前期气象干旱得到解除。