Millennial‐scale variability in the oceans: an ocean modelling view

Climate and ocean‐only models have shown that the ocean will respond abruptly to significant perturbations in surface forcing. Centennial‐scale oscillation is a characteristic of circulation in large semi‐enclosed ocean basins such as the Arctic, whereas millennial‐scale adjustment to changes in surface forcing has been found in the global ocean component of climate models. We show that the millennial time‐scale in climate models is likely to be intrinsic to the ocean through its presence in an ocean‐only model. The strength of the thermohaline circulation is shown to be very sensitive to the magnitude of ice albedo and, to a lesser extent, perturbation in the surface freshwater flux. Modelled glacial ocean circulation, in contrast to present‐day simulations, requires an enhanced freshwater flux over the northern Atlantic, even in its non‐Heinrich state, to obtain realistic overturning in the North Atlantic. Copyright © 2001 John Wiley & Sons, Ltd.     

A Late Quaternary Climate Record Based on Multi-Proxies Analysis from the Jiaochang Loess Section in the Eastern Tibetan Plateau, China

We compared the stable carbon isotopic records from a loess transect of the Jiaochang in the eastern Tibetan Plateau, spanning the last ~21,000 years, with multiproxy data for pedogenesis, including magnetic susceptibility, clay fraction, Fed/Fet ratio, carbonate and total organic carbon content, in order to probe the mechanisms of δ13C values of organic matter and Late Quaternary climate variations in the eastern Tibetan Plateau. Our results indicate that there is no simple relationship between δ13C of organic matter and summer monsoon variations. The change in δ13C values of organic matter (in accordance with the ratios of C3 to C4 plants) results from the interaction among temperature, aridity and atmospheric pCO2 level. Drier climate and lower atmospheric pCO2 level contribute to positive carbon isotopic excursion, while negative carbon isotopic excursion is the result of lower temperature and increased atmospheric pCO2 level. Additionally, our results imply that the Tibetan monsoon may play an important role in climate system in the eastern Tibet Plateau, which specifically reflects frequently changing climate in that area. The results provide new insights into the forcing mechanisms on both the δ13C values of organic matter and the local climate system.     

亚洲中部天山—贝加尔陆内变形终止边界

亚洲中部,沿天山的西端、阿尔泰山的西北端到贝加尔地区,是一条显著的NE向边界(天山—贝加尔边界),在它的两侧,地形、构造、地震活动和其他地球物理特征都有显著的差异。沿这条边界不存在同方向的大断层,同时,一系列NW向大型走滑断层与这条边界以大角度相交,这些断层的西北段在边界西北侧附近终止。总体上,这条边界西北侧是稳定的哈萨克斯坦地台和西伯利亚地台,东南侧主要是构造活动的天山、阿尔泰山及蒙古西部,因此,这条NE向构造边界是大陆内部的变形终止边界。中亚地区的陆块拼合过程在古生代末已结束,天山、阿尔泰山等造山带与北边的哈萨克斯坦地台和西伯利亚地台焊接为一体,经历中生代的固化。新生代以来,受印度-欧亚板块碰撞的影响,天山、阿尔泰山等造山带在NS向挤压力作用下发生变形,包括近东西向逆断层和NW向走滑断层的活动以及分散的地震。这些变形向北扩展时,被刚性、结构完整的哈萨克斯坦地台和西伯利亚地台截断终止,因而造成NE向天山—贝加尔边界。亚洲大陆内部块体的地壳强度和变形特征有明显的继承性,新生代以来,原来的地台(克拉通)继续保持结构完整和稳定性,几乎没有内部变形,而天山、阿尔泰山等古老的造山带则再次经历强烈变形。这不仅是由于印度板块继续向北推挤的影响,而且与这些地区自身的地壳和上地幔结构有关,同时NE向天山—贝加尔边界的西北侧哈萨克斯坦地台和西伯利亚地台对变形扩散的阻挡也起了重要作用。     

Progressive glacial retreat in the Southern Altiplano (Uturuncu volcano, 22°S) between 65 and 14 ka constrained by cosmogenic He dating

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic ³He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these ³He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65 ka, with an equilibrium line altitude (ELA) at 5280 m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40 ka, and another one between 35 and 17 ka, followed by a limited recession at 17 ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14 ka, with an ELA standing at 5350 m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450 m after 14 ka, synchronously with the Bolling–Allerod.     

巴丹吉林沙漠东南缘末次冰期沉积物地球化学特征及气候指示意义

沙漠古气候重建对于了解区域古气候演变具有重要意义.通过以巴丹吉林沙漠东南缘巴润宝日陶勒盖(BRBG)剖面为研究对象,进行全样地球化学、分组分分粒级元素地球化学及Sr同位素分析,重建该地区末次冰期期间(66.8～41.0 ka)的气候演化模式.研究表明:66.8～41.0 ka呈现残留组分高Sr/Ca值、酸溶组分及残留组...     

南海东北部末次冰期以来沉积环境演变

利用南海东北部上陆坡处所取的D孔(21°23′02″N,116°47′13″E,水深405m)进行硅藻分析,结合粒度分析与碎屑矿物分析结果,探讨该海域末次冰期以来沉积环境演变过程。结果表明:粒度与硅藻分析结果较为吻合,共同显示D孔可分为上下两层,上层(0-2cm)的砂质沉积层为经冰后期海进过程改造的晚更新世残留沉积层;下层(2-130cm)主要是末次冰期形成的浅海沉积。整个柱样可反映出海洋同位素MIS4期海退至MIS3期海进与MIS2期海退至冰后期海进的沉积韵律。     

南海深水区末次冰期和冰后期沉积物堆积速率的特征

通过统计南海100 m以下深水区的136个沉积柱状样的分析数据,对南海末次冰期以来的堆积速率进行了统计.计算出MIS(marine isotope stage)1期的年均沉积量为152.3 Mt/a,2期的为215.2 Mt/a,主要为陆源物质的贡献.无论在末次冰期还是在冰后期,堆积速率均在南海西南部最高,其次是在东北部,在其他地区较低.由于侧向搬运和顺坡搬运频繁,虽然整体上末次冰期的堆积速率高于冰后期的,但在沉积物高速堆积地区附近有相反的变化趋势.     

Accurate Determination of Sr Isotopic Compositions in Clinopyroxene and Silicate Glasses by LA‐MC‐ICP‐MS

The low‐Sr content (generally < 100 μg g^?1) in clinopyroxene from peridotite makes accurate Sr isotopic determination by LA‐MC‐ICP‐MS a challenge. The effects of adding N₂ to the sample gas and using a guard electrode (GE) on instrumental sensitivity for Sr isotopic determination by LA‐MC‐ICP‐MS were investigated. Results revealed no significant sensitivity enhancement of Sr by adding N₂ to the ICP. Although using a GE led to a two‐fold sensitivity enhancement, it significantly increased the yield of polyatomic ion interferences of Ca‐related ions and TiAr⁺ on Sr isotopes. Applying the method established in this work, ⁸⁷Sr/⁸⁶Sr ratios (Rb/Sr < 0.14) of natural clinopyroxene from mantle and silicate glasses were accurately measured with similar measurement repeatability (0.0009–0.00006, 2SE) to previous studies but using a smaller spot size of 120 μm and low‐to‐moderate Sr content (30–518 μg g^?1). The measurement reproducibility was 0.0004 (2s, n = 33) for a sample with 100 μg g^?1 Sr. Destruction of the crystal structure by sample fusion showed no effect on Sr isotopic determination. Synthesised glasses with major element compositions similar to natural clinopyroxene have the potential to be adopted as reference materials for Sr isotopic determination by LA‐MC‐ICP‐MS.     

漓江流域末次冰期以来气候环境变化研究进展

为更好地认识漓江流域过去气候环境变化,更好服务于漓江流域未来气候环境预测、生态环境建设及资源环境可持续发展,本文对漓江流域末次冰期以来的气候环境研究现状进行了总结和综述。总结了年代学、现代过程研究、古气候环境重建和古人类演化方面的进展及存在的问题,并对下一步的研究方向进行了分析和探讨。希望能促进华南地区过去气候环境变化研究,并对经济社会可持续发展提供借鉴和参考,助力桂林可持续发展创新示范区建设。     

中国干旱、半干旱区末次冰期以来气候变化规律

以临夏塬堡末次冰期中晚期黄土剖面为基础,选用我国干旱、半干旱区末次冰期以来同期异相或同期同相的气候记录与研究剖面进行对比分析后表明：位于西风气流控制的新疆地区全新世气候总体表现为偏干偏冷,晚期较为温暖的特点．其气候波动的幅度和频率较低。而位于季风环流控制的其它地区．全新世气候变化反映了同样的变化规律,即早全新世的升温波动期、中全新世的温暖稳定期和晚全新世的变冷期,其气候波动的幅度和频率较快。而无论是西风气流控制的新疆地区,还是季风环流影响的其它我国干旱、半干旱区,末次冰期气候变化均表现为早晚期的干冷期和中期的温湿期,尽管其干冷和温湿的程度不尽相同。