最新观测发现深海水循环中对流作用的机理

异重水在全球温盐合成环流系统中起重要作用，它的形成与深层对流有关。本文通过混合层低温脉冲与加入边界深洋流的异重水特性比较，提出了深层环流作用机理，并利用机理进行预测，与实测结果相符，证明了所提深层环流作用机理的正确性。     

温室气体浓度增加情景下大西洋温盐环流的演变

温室气体浓度增加(以CO2为主)引起的温盐环流演变在未来气候系统中扮演非常重要的角色.在最新的温室气体排放情景下,利用基于德国马普气象研究所为IPCC第四次评估报告而最新发展的气候模式(ECHAM5/MPIOM),对3种不同的温室气体排放假设(B1,A1B,A2)进行了可靠的数值模拟.在此基础上,就大西洋温盐环流和北大西洋深层水形成的变化,以及北大西洋不同海区的温盐环流对温室气体浓度增加的响应,对模拟结果进行了分析.研究揭示,到21世纪末,在3种CO2排放情景下,温盐环流强度分别减弱了4Sv(1Sv=106m3/s)、5.1Sv、5.2Sv,大体相当于减弱了20%、25%、25.1%.由于全球变暖引起副极地海区表层海水变暖变淡,拉不拉多海(LabradorSea)和丹麦海峡(DenmarkStrait)以南区域的深层对流有所减弱.而在格陵兰-冰岛-挪威海(GINSea)的情况相反,由于北大西洋暖流的增强,通过法鲁海峡(Faro-BankChannel)进入GIN海域的高盐水增加,导致GIN海域上层盐度(密度)增加,进而深层对流加强.在A1B情景下,由于全球变暖北大西洋的深层水生成率从16.2Sv降到了12.9Sv.     

极地地质钻探研究进展与展望

南北极在全球海平面变化和碳循环中扮演着关键角色,并蕴藏着地球如何从新生代初期的温室转向现代冰室演变过程的关键信息,因而成为地球科学研究的热点地区。极地地质钻探计划(如DSDP/ODP/IODP/ICDP)研究所取得的成就令人瞩目,刷新了人类对过去全球变化的认识,成为探究地球气候系统演化的一个窗口。通过这些钻探计划,发现了新生代以来气候变冷,南北极冰盖几乎同时形成;揭示了南极冰盖形成和陆地风化的加剧,导致南极中深层水和底层水的生产加速并向北推进,造成全球大洋环流的重大变化;南大洋对大气CO_2的调控作用、全球大洋深部循环、营养盐的分布和海洋生产力等多方面在不同时间尺度上都发挥着重要作用;检验了南北极冰盖形成和消融与海平面变化的关系,为人类预测未来海平面变化提供了历史依据。未来的南北极国际大洋发现(IODP)计划将继续关注于极地冰盖的演变历史、南大洋古海洋学演变历史,追踪北极海—陆环境的联系及其对全球气候的影响。这些结果将对未来全球气候预测提供重要的参考和边界条件。     

西非裂谷系Termit盆地古近系油气成藏主控因素分析

Termit盆地隶属于西非裂谷系,是发育于前寒武系-侏罗系基底之上的中、新生代裂谷盆地。国外石油公司自1974年开始对该盆地进行勘探,截止2008年在中国石油获得勘探许可前,仅在西部Dinga断阶带发现7个油气藏,区域甩开勘探没有获得商业发现。针对这一国外石油公司勘探近40年后放弃的区块,面临着如何寻找潜力区带、发现规模油气的巨大挑战。本文基于Termit盆地晚白垩世大规模海侵、早白垩世和古近纪两期裂谷叠置的构造演化特点,分析了古近系油气成藏的主控因素。这种后期叠置裂谷(古近纪)的成藏模式有别于其他纯陆相单一旋回的裂谷盆地,烃源岩为上白垩统海相泥页岩,储层为古近系陆相砂岩,盖层为古近系湖相泥岩,表现为跨世代(跨二级层序)油气聚集特征。其油气成藏具有6个主控因素,即大范围海相烃源岩“控源”、叠置裂谷“控砂”、断裂与砂岩输导层“控运”、构造地貌“控势”、断层与砂体配置“控藏”、盖层与侧向封挡“控保”。成藏主控因素分析揭示了Termit盆地古近系的油气富集规律,有效指导了该盆地潜力区带评价与规模油气发现。     

欧亚海盆大西洋水输运过程及热释放研究进展

温暖的大西洋水进入北冰洋后,通过热量释放影响海洋和大气环境。在欧亚海盆,大西洋水深度浅,其热量释放是海冰融化的重要热源,也是海冰减退和北极放大的关键因素。大西洋水输送的环流结构没有变化,而是通过流速的变化改变热量输送的效率。大西洋水在流动过程中通过湍流运动、冬季对流和双扩散三大物理机制向上释放热量而降温。近年来,大西洋水热量增加并将暖信号向北冰洋内部输送,进而影响下游加拿大海盆的海洋过程。增暖的热源来自弗拉姆海峡的异常暖事件,体现为北欧海挪威大西洋流水温长期变化因素与低频振荡因素的共同作用。     

内蒙古查干凹陷的构造格架与演化

查干凹陷发育于华北板块西北缘的古造山带基础之上,属造山期后的伸展垮塌型盆地。位于该凹陷东南部的“毛敦侵入体”和“毛东断层”主要形成于前白垩纪,均为盆地基底的查干础鲁深大断裂带的重要组成部分;前人所划分的“罕塔庙次凹”主体可能为前白垩系残留地层,而并非早白垩世断陷沉积。凹陷的构造格架受不同级次的断层带控制;主要构造样式可分为伸展构造、挤压构造、反转构造和具有走滑分量的构造4大类,并以伸展构造为主体。该区白垩纪-新生代的构造演化经历了伸展断陷发生、发展、弱伸展断-坳转化、稳定坳陷和挤压改造5个阶段。     

柴达木盆地北缘构造控藏特征与油气勘探方向

柴北缘油气成藏特征及油气分布受构造控制明显,但由于构造体系复杂,因此油气成藏主控因素及主要勘探方向不明。研究表明,由于柴北缘缺乏主要滑脱层,在晚新生代强烈挤压与走滑调整的控制下主要发育基底卷入式构造,形成上、下构造层变形相对一致的“破碎型”构造体系。柴北缘油气成藏条件、晚新生代两期成藏及其与构造形成时间的匹配关系决定了古近纪继承性古构造是油气运聚的有利部位,而喜山晚期构造调整使得油气分布复杂化,古构造发育、晚期改造强度与烃源岩演化、充注成藏的匹配关系决定了古近纪继承性古构造向凹陷延伸的侧翼部位是柴北缘油气勘探的有利部位,应坚持“破碎型”构造体系中相对稳定区的油气勘探。     

扬子东南大陆边缘晚前寒武纪古海洋演化的稀土元素记录

本文采用中子活化方法分析了晚震旦～早寒武纪１９件样品的稀土元素组成,发现硅质岩石ＲＥＥ配分形式有着复杂的变化,初步可以划分为五种类型,包括“台地型”、“红海型”、“海水型”及两种特殊的配分形式。剖面上Ｃｅ异常由小到大的演变反映了古海洋底层水由缺氧环境向氧化条件的逐渐转化。正Ｅｕ异常的出现代表了热水沉积事件的存在。     

早新生代温室气候及冰期气候转型的模拟研究

早新生代是地质史上最后一个温室气候期，随后南极冰盖形成，地球进入到晚新生代冰期。温室气候的成因和冰期气候转型的机制一直是国际相关学界关注的问题。评述国际上对此开展的古气候模拟，反映了早新生代温室气候受到了海洋和大陆的地理位置、暖海洋温盐环流和海洋热输送、太阳辐射和大气CO2浓度变化的作用和影响。古气候模拟还反映了早新生代温室气候转向冰期气候，受到了大洋通道改变和高原构造隆起、大气成分变化以及海陆生态系相互的作用和反馈。这些古气候模拟试验锁定在气候变化的关键时段和重要驱动因子，对测试地球内外驱动力和地球各圈层反馈作用提供了重要的科学依据；温室气候以及趋向冰期气候的模拟研究对探讨气候变化内在机制、预测未来气候具有重要意义。      

再论偏岭石与变高岭石的区别--评《天然烧变高岭石中水铝英石的发现》一文

《矿物学报》１９９５年第４期发表了何宏平的“天然烧变高岭石中水铝英石发现”一文。该文用核磁共振谱中－７９.０×１０－６附近的谱峰,认为该信号来自水铝英石,而不是来自Ａｌ－Ｓｉ尖晶石。这种说法较合理,因刘长龄早就阐明偏岭石在成岩阶段由水铝英石变来。但是我们不同意“天然煤烧变高岭石经后期水化作用变成水铝英石”的观点,而主张“水铝英石是沼泽相原生沉积的;在成岩作用中转变为偏岭石不是煤烧的,有一些理化性质与变高岭石的不同”     

Global Cenozoic Paleobathymetry with a focus on the Northern Hemisphere Oceanic Gateways

The evolution of the Northern Hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the Cenozoic time (66 Ma–0 Ma). However, the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions. We have therefore re-evaluated the evolution of the Northern hemisphere oceanic gateways (i.e. the Fram Strait, Greenland–Scotland Ridge, the Central American Seaway, and the Tethys Seaway) and embedded their tectonic histories in a new global paleobathymetry and topography model for the Cenozoic time. Our new paleobathymetry model incorporates Northeast Atlantic paleobathymetric variations due to Iceland mantle plume activity, updated regional plate kinematics, and models for the oceanic lithospheric age, sediment thickness, and reconstructed oceanic plateaus and microcontinents. We also provide a global paleotopography model based on new and previously published regional models. In particular, the new model documents important bathymetric changes in the Northeast Atlantic and in the Tethys Seaway near the Eocene–Oligocene transition (~34 Ma), the time of the first glaciations of Antarctica, believed to be triggered by the opening of the Southern Ocean gateways (i.e. the Drake Passage and the Tasman Gateway) and subsequent Antarctic Circumpolar Current initiation. Our new model can be used to test whether the Northern Hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time. In addition, we provide a set of realistic global bathymetric and topographic reconstructions for the Cenozoic time at one million-year interval for further use in paleo-ocean circulation and climate models.     

Seasonally ice free glacial nordic seas without deep water ventilation

At present the Nordic Seas are a key region of North Atlantic Deep Water (NADW) formation. Two alternative scenarios have been suggested by some authors for the Last Glacial Maximum: (i) the Nordic Seas were permanently covered by sea ice, preventing the formation of NADW, or (ii) that they were seasonally free of ice and that deep water formation did occur. A modified scenario is presented here based on parallel ocean circulation modelling results from the GFDL primitive equation model and a planetary geostrophic model. It is suggested that the glacial Nordic Seas were at least seasonally ice free, but it is observed that there was never deep water formation from the surface; rather it occurred only in the North Atlantic south of 40°–50°N. North of 40°N, the weaker LGM northward flowing thermohaline conveyor is subducted below a reverse conveyor which occurred to a depth of over 1000 m. Various modelling experiments presented here indicate that the reversed conveyor was primarily caused by the colder conditions of the glacial North Atlantic that led to far stronger zonality of glacial analogue of the North Atlantic Current.     

Modeling ocean–atmosphere carbon budgets during the Last Glacial Maximum–Heinrich 1 meltwater event–Bølling transition

Benthic carbon isotope data indicate that the rate of North Atlantic Deep Water (NADW) formation and the mode of oceanic thermohaline circulation (THC) varied considerably across the transition from the Last Glacial Maximum (LGM) to the Heinrich 1 meltwater event (MWE) and, subsequently, to the Bølling warm period. We simulate changes in the Ocean-atmosphere carbon cycle induced by and linked to these oceanic fluctuations by means of a carbon cycle box model which resolves the major oceanic basins. The output from an ocean general circulation model (OGCM), which is forced by observed or reconstructed boundary conditions at its surface, serves to constrain the physical parameters of the carbon cycle model. The OGCM depicts three modes of Atlantic THC: an interglacial mode with vigorous NADW formation; a glacial mode with active, although weaker (-65%) NADW formation; and an MWE mode characterized by the complete lack of NADW formation. The carbon cycle model is forced from the LGM scenario into the MWE and finally into the Bølling interstadial. The glacial circulation mode accounts for approximately half (i.e., 37Dž µatm, depending on parameterization of biological productivity) of the observed glacial reduction in atmospheric CO₂ partial pressure (pCO₂). Approximately 70% of this pCO₂ decline is linked to changes in sea-surface temperature and salinity. The MWE circulation mode has only a small effect on atmospheric pCO₂ (ǃ µatm) but goes along with a massive redistribution of carbon from the Indo-Pacific and Southern oceans to the Atlantic Ocean, which stores 85NJ Gt (gigatons) excess carbon during the MWE. The onset of NADW formation after a meltwater event, has the potential to release 81Lj Gt carbon from the model ocean to the atmosphere, corresponding to an atmospheric pCO₂ increase by 38Dž µatm, equivalent to approximately half of the modern, man-made pCO₂ load.     

Atlantic ocean heat piracy and the bipolar climate see‐saw during Heinrich and Dansgaard–Oeschger events

The millennial‐scale asynchrony of Antarctic and Greenland climate records during the last glacial period implies that the global climate system acts as a bipolar see‐saw driven by either high‐latitudinal and/or near‐equatorial sea‐surface perturbations. Based on the results of recent modelling of generic Heinrich and Dansgaard–Oeschger scenarios, we discuss the possibility that oscillations of the deep‐ocean conveyor may have been sufficient to cause this bipolar see‐saw. The bipolar climate asynchrony in our scenarios is caused by the toggle between North Atlantic heat piracy and South Atlantic counter heat piracy. Ocean circulation has an enhanced sensitivity to the northern deep‐water source as the North Atlantic Deep Water (NADW) cannot enter the Southern Ocean at depths shallower than the bottom of the Drake Passage. Any shoaling of the NADW can, therefore, increase the northward incursion of Antarctic Bottom Water (AABW), and trigger an interhemispheric climate oscillation. As hundreds of years are required to warm the respective high latitudes, the observed climate lead and lags between the two hemispheres can be explained entirely by the variability of the meridional overturning and by the corresponding change in the oceanic heat transport. Accordingly, it is entirely feasible for the global climate to work like a pendulum, which theoretically could be controlled by pushing at either of the deep‐water sources. Our model scenarios suggest that it is entirely feasible for the bipolar climate see‐saw to be controlled solely by variations in NADW formation. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

北欧海深层水的研究进展简

As a connection region between North Atlantic and Arctic Oceans, the Nordic Sea plays a critical role in global climate system. In the Nordic Seas, surface water converts into intermediate water and deep water after cooling and other effects. These waters transport southward, and enter into North Atlantic as a form of overflow, therefore, they are the main source of the North Atlantic Deep Water(NADW), which play a key role in global ocean conveyor. The causes and processes of the deep water formation in the Nordic Seas are still uncertain. Based on a review of current and historical research results of the deep water in the Nordic Seas, the most important process for deep water formation convection is addressed. Factors and physical processes that may have impact on deep water formation are summarized. The transport of deep water in the Nordic Seas is summed up. Multi year variation of the deep water is described with the aim of giving some instructions and research directions to the readers.     

北极海冰与全球气候变化

最近有关北极海冰在全球气候系统中作用的研究发现，北冰洋边缘海域大洋深水的形成与海冰发育有关，海冰冻融过程对盐度层结具有重要影响，海冰变化可引起盐度突变层的灾变和热盐环流的突然停止，热盐环流的变化与北大西洋海冰１０年际变化相联系，北大西洋气候的不稳定性与热盐环流变化密切相关。北极海冰－海洋－大气间耦合作用，使北极海冰构成了北大西洋和全球气候反馈循环中的重要环节。     

A regional 8200 cal. yr BP cooling event in northwest Europe,induced by final stages of the Laurentide ice-sheet deglaciation?

The most notable change in δ¹⁸O in Greenland ice cores during the Holocene occurs at 8200 cal. yr BP. Here we present a new high-resolution marine record from the northern North Sea, along with tree-ring data from Germany, which contain evidence of a pronounced temperature drop (>2°C) contemporaneous with that of the Greenland ice-core records. The synchronous timing of the cooling event in the Greenland ice-cores, marine record and tree-ring data from northwest Europe reflects a regional influence on the North Atlantic ocean–atmospheric system, suggesting a prominent role of the North Atlantic thermohaline circulation. The operation of the North Atlantic ocean circulation is sensitive to variation in the freshwater budget, implying that any change in freshwater flux is capable of altering the North Atlantic circulation system. We hypothesise minor but long-term freshwater fluxes in the final stages of the deglaciation of the Laurentide ice-sheet as a forcing mechanism. © 1998 John Wiley & Sons, Ltd.     

Link of ocean deep water thermohaline anomalies with atmospheric state anomalies in the Northern Atlantic

Anomalies of thermohaline characteristics of the ocean deep waters formed in the subpolar North Atlantic are shown to be controlled by the natural oscillations of the atmospheric state in the region, i.e., the North Atlantic Oscillation (NAO). A general mechanism behind the NAO effect on the deep water temperature and salinity on a decadal time scale is proposed. The main factors determining the close link of the deep water thermohaline anomalies and the NAO are the zonal extension of the subpolar gyre and the wintertime deep convection intensity in the Labrador Sea.     

大洋热盐环流研究的一个焦点：北太平洋是否有深水形成

现代大洋热盐环流的特点之一是北大西洋有深水形成而北太平洋没有，这种不对称性对周边气候产生了重要影响。尽管理论上认为大洋热盐环流可能存在对应不同气候的多平衡态，但北太平洋是否曾有过深水形成已成为目前学术争论的一个热点。简要介绍了最新的热盐环流研究成果，重点分析现代北太平洋无深水形成的原因，其中亚洲季风的水汽输送和低蒸发是两个重要的影响因子。