季节性海冰驱动的冰期北大西洋“电容器”效应     

张旭  张炜晨  王振乾  郑凯  邓凤飞 《地学前缘》2022,29(5):334-341

第四纪冰期的千年尺度气候突变事件——Dansgaard-Oeschger Event (D-O事件),一直是古气候学领域关注的重点。近年来,数值模拟的研究发现,北大西洋副极地地区年际-年代际气候变率的振幅在D-O事件中的冰阶冷期远大于间冰阶暖期,这一现象为理解该区域海温代理指标的气候学意义提供了重要参考价值,但其动力机制尚不清晰。本文利用海气耦合气候模型(COSMOS),通过模拟氧同位素(MIS)3阶段的一个典型D-O事件过程,探讨了冰阶冷期北大西洋气候变率的放大机制。结果显示,北大西洋副极地海域的季节性海冰通过调控海气间热量交换,影响当地气候变率的幅度。冰阶期,热带暖水向北输送导致海洋次表层逐渐升温,削弱了表层-次表层海水的密度层结,有利于次表层暖水上涌,促进海冰融化及海表温度升高。这将激发出海平面气压的负异常,引起气旋式风切变,并通过Ekman抽吸作用加速表层-次表层海水的垂直混合,进一步促进次表层暖水的上涌。这一正反馈机制造成海洋次表层热量的迅速释放,海表温度快速升高。当次表层热量释放结束后,海表将无暖水补充,导致海表温度下降,海冰增多。该过程激发的海表气压正异常(即反气旋式风切变)将抑制垂直混合发生,促进次表层热量积累,为下一次放热过程提供条件。在间冰阶暖期,随着北大西洋季节性海冰消失,海气间热交换不再受海冰变化影响,海洋次表层与大气间的热交换始终处于准平衡态,气候变率的振幅显著下降。本研究结果显示,北大西洋季节性海冰的存在可以调控海洋次表层热量积累-释放的过程,产生“电容器”效应,这对理解冰期年际-年代际气候变率放大现象有重要启示意义。  相似文献   

Chronostratigraphic framework and depositional environments in the organic‐rich,mudstone‐dominated Eagle Ford Group,Texas, USA     

《Sedimentology》2018,65(5):1520-1557

Since the beginning of the century, several authors have hypothesized and documented the presence of bottom currents during the deposition of mudstones, including mudstones rich in organic matter, challenging the assumption that persistent low‐energy conditions are necessary prerequisites for deposition of such sediments. More processes responsible for transport and deposition of mudstones mean also more processes acting contemporaneously in different parts of a basin. Without a precise and robust chronostratigraphic framework, however, it is not possible to characterize these differences. The new data reported here provide a profoundly different understanding of the controls on sedimentation in distal continental shelf platforms. To enhance the understanding of the different coeval environments of deposition coexisting in a muddy system, the Upper Cretaceous Eagle Ford Group, deposited on the Comanche carbonate platform, has been investigated by integrating sedimentology, mineralogy, geochemistry and palaeoecology, and creating age models in different physiographic sectors using biostratigraphy and geochronology. Data from two cores and 41 outcrops were analysed with a telescopic approach, from grain scale to basin scale. Nine temporal stages over a ca 8 Myr interval (ca 98 to 90 Ma) were defined in an area that spans 75 000 km². Finally, the different environments of deposition recorded within each of the nine stages were interpreted. The construction of the chronostratigraphic framework also allowed: measuring the duration of a basin‐wide gradational increase in energy in the water column (ca 1 Myr) and a hiatus confined into the shallower water sector (ca 2 Myr); determining the mean eruption frequency of volcanoes (ca 9 kyr); and the time of inundation of the Western Interior Seaway (97·5 to 97·1 Ma). The context, the outcrops–cores–logs correlations, the large data set (Appendix  S1 ), the high‐precision and well‐calibrated constraints represent an unprecedented contribution for future regional facies models of organic‐rich units and for improvements of key aspects in the industry of unconventional resources.  相似文献   

内蒙古地区极端降水事件分布特征   总被引：3，自引：1，他引：2  

刘宏伟  刘秀荣  陈凌云 《内蒙古气象》2009,(6):7-9

基于内蒙古地区94个气象站1961—2007年逐日降水量资料,利用累积频率法,分析了极端降水事件变化特征。结果表明:(1)近50年内蒙古地区极端降水事件和极端强降水事件发生的强度和出现的频次均呈现出增多趋势,尤其在1977年降水发生突变之后,增加趋势更为明显。(2)近50年内蒙古地区最长连续无降水日数和最长连续降水日数持续时间缩短,表明连续性干旱和降水的持续性减弱,尤其是进入本世纪后,最长连续无降水日数陡升和最长连续降水日数陡降,气候湿润程度下降,加之全球气候变暖,使内蒙古地区进入本世纪后暖而干的气候特征更为明显,这对农牧业生产和生态环境保护极为不利。(3)内蒙古地区近50年小雨和暴雨日数的减少,降水强度的加大,使全区降水不稳定性增加,降水有极端化发展趋势,尤其是在1987年气温发生突变之后,降水强度变化更大。  相似文献   

Event chronostratigraphy: A high-resolution tool for dating the recent past   总被引：2，自引：1，他引：1  

S.J. Gale   《Quaternary Geochronology》2009,4(5):391-399

The most recent part of the geological timescale presents us with some of the greatest challenges for dating. With the exception of ²³⁰Th/²³⁴U methods, whose use is restricted to rather specific depositional environments, there is no established geochronometric tool capable of dating more than a fraction of the recent past at a resolution adequate to tackle the environmental issues of this period. Event stratigraphy, the investigation of comparatively rare and abrupt occurrences that leave some trace in the stratigraphic record, has been widely employed as a means of correlation and dating of older geological strata. Yet this approach has frequently been overlooked in efforts to establish chronologies of the recent past. It is ironic, therefore, that because of the acceleration of human activity, stratigraphic events have almost certainly occurred with greater frequency over the last few centuries than at any preceding time in Earth history. Because the history of human-induced events is usually well-established, the markers of such events have immense chronostratigraphic value. They may be employed in circumstances in which radiometric techniques may not be suitable, and may offer higher-resolution dates than those associated with conventional dating methods. Dated event horizons may also provide the essential means by which to validate geochronometric analyses of the recent past.Event markers may be divided into those that produce discontinuities in the rock record and those (of much greater value in the terrestrial deposits that are the focus of most investigations of the recent past) that leave some tangible signal in the rocks. These signals may be the result of either natural factors or human-induced processes, and may occur in a range of temporal contexts. They may mark the instant of occurrence of a short-lived phenomenon, or they may represent the abrupt disappearance or sudden appearance of some feature. This paper reviews each of these markers, focussing specifically on their application to the chronology of the recent past and the global environmental transformation that has taken place during this time.  相似文献   

Dating the recent past   总被引：2，自引：1，他引：1  

S.J. Gale   《Quaternary Geochronology》2009,4(5):374-377

The dramatic environmental changes of the last 500 years are likely to continue into the future and to have an increasing impact on both the Earth and human society. Any understanding of future environmental change is thus critically dependent on our capacity to reconstruct the environmental changes of the past. Fundamental to this is an ability to place the environmental responses of the last half millennium within a reliable chronological framework. Unfortunately, this most recent part of the geological timescale presents us with some of the greatest challenges for dating. With the exception of ²³⁰Th/²³⁴U methods, whose use is restricted to the rather specific depositional environments of shallow marine and terrestrial carbonates, there is no established geochronometric tool capable of dating more than a fraction of the recent past at a resolution adequate to tackle the environmental issues of this period. This challenge has been met by refining existing procedures (including ¹⁴C, ⁴⁰Ar/³⁹Ar, event chronostratigraphy and optically stimulated luminescence) and developing new ones (such as ³²Si). These offer a means of calibrating the high-resolution environmental records of the last 500 years and answering the critical environmental questions presented by this period.  相似文献   

国家测震台网中心强震动数据处理系统的设计与实现     

刘艳琼  邹立晔  房立华  梁姗姗  任枭  张琪  李旭茂  沈玉松  苏柱金 《中国地震》2024,40(1):110-120

为满足国家测震台网海量强震动观测数据的处理时效性、格式标准化、产品丰富度等需求,开发了兼容多类强震动观测站点且具备数据快速汇集、处理及归档等功能的强震动数据处理系统。该系统提供地震波形人机交互数据预处理界面,对加速度记录进行预处理,进一步分析预处理后的加速度事件波形数据,计算得到地震动各项参数,包括峰值加速度(PGA)、峰值速度(PGV)、峰值位移(PGD)、仪器烈度、持时、傅氏谱、反应谱和三联谱等,可以导出地震元数据、地震记录波形,对各类数据进行归档存储。该系统具有平台统一性、功能集成性、数据完备性等特点,有效提升了日常数据处理和管理能力,能在地震应急、震害评估和科学研究中发挥实效。  相似文献   

近百年来亚洲中部内陆湖泊演变及其原因分析   总被引：7，自引：1，他引：6  

秦伯强 《湖泊科学》1999,11(1):11-19

南疆博斯腾湖湖相沉积物碳酸盐稳定同位素,孢粉及地化元素含量的波动揭示了于１１．０￣１０．０ｋａＢＰ期间的相对冷湿的环境特征,这次变冷事件在年代上可与末次冰消期的新仙女木气候突然变冷事件相对应,虽然目前还无法圆满解释此事件的成因机制,但此事件在极端干昌的南疆博斯腾湖湖相沉积中的发现,无疑对深入认识此事件发生的全球性以及探讨其成因机制具有重要意义。  相似文献   

华北陆块2.56～2.52 Ga增氧事件对成矿和生命演化的影响     

沈保丰  毕君辉  张阔 《地质学报》2021,95(2):336-351

地球表层大气氧浓度的显著增高是地球史上最重大的地质事件之一,它不仅改变了地球表层环境,促进了生命演化,而且加速了表生地质过程,形成一系列适应环境突变的岩石和重要矿床.地球在前寒武纪时期曾发生过两次大气快速增氧事件,分别为大氧化事件(GOE)和新元古代氧化事件(NOE).本文主要论述华北陆块新太古代晚期增氧事件的时限及其...  相似文献   

爆破、塌陷识别研究进展综述     

周少辉  蒋海昆  曲均浩  李健  郭宗斌  郑旭 《中国地震》2021,37(2):508-522

简要介绍当前国内外关于天然地震与爆破、塌陷等非天然地震特征研究及事件类型识别的进展.对各类事件的定义及主要波形特征进行简要综述,重点介绍了事件类型判定的各类识别方法.与自然界天然地震不同,非天然地震由人工干预或人类活动间接引发.爆破是炸药在爆炸瞬间能量迅速释放,部分能量以地震波形式向外传播,引起地表振动而产生破坏效应的...  相似文献   

Security and the future: Anticipating the event of terror   总被引：1，自引：0，他引：1  

Ben Anderson 《Geoforum》2010,41(2):227-235

This paper explores the relation between processes of security and futurity in the context of efforts to govern the complexity and contingency of events of terror. It argues that processes of securing function by generating a dangerous or promissory supplement to the present that thereafter propels the extension of forms of security. The paper develops this argument through an example of how an event of terror was anticipated: a RAND exercise into the aftermath of a ‘ground burst’ nuclear explosion in Long Beach, California on March 14th 2005. It argues that exercises (in)secure through three quasi-causal operations, each of which render events of terror actionable and result in specific relations between the present and future. First, ‘hypothetically possible’ generic events are named. The future takes place as a threatening horizon. Second, the defined phases of an event’s happening are staged (an advent, its multiplication into a crisis in the context of a milieu, and a response/recovery phase). The here and now is suspended between an ‘as if’ future and the present. Third, the consequences of the event are played. The future is both an intensified ‘practical’ presence embodied by exercise participants and an outside that exceeds attempts to definitively know it. The conclusion summarises the implications of the paper for work on futurity, security and the event.  相似文献