Orbital changes and climate

At the 41,000-period of orbital tilt, summer insolation forces a lagged response in northern ice sheets. This delayed ice signal is rapidly transferred to nearby northern oceans and landmasses by atmospheric dynamics. These ice-driven responses lead to late-phased changes in atmospheric CO₂ that provide positive feedback to the ice sheets and also project ‘late’ 41-K forcing across the tropics and the Southern Hemisphere. Responses in austral regions are also influenced by a fast response to summer insolation forcing at high southern latitudes.At the 22,000-year precession period, northern summer insolation again forces a lagged ice-sheet response, but with muted transfers to proximal regions and no subsequent effect on atmospheric CO₂. Most 22,000-year greenhouse-gas responses have the ‘early’ phase of July insolation. July forcing of monsoonal and boreal wetlands explains the early CH₄ response. The slightly later 22-K CO₂ response originates in the southern hemisphere. The early 22-K CH₄ and CO₂ responses add to insolation forcing of the ice sheets.The dominant 100,000-year response of ice sheets is not externally forced, nor does it result from internal resonance. Internal forcing appears to play at most a minor role. The origin of this signal lies mainly in internal feedbacks (CO₂ and ice albedo) that drive the gradual build-up of large ice sheets and then their rapid destruction. Ice melting during terminations is initiated by uniquely coincident forcing from insolation and greenhouse gases at the periods of tilt and precession.     

Earth dynamics and climate changes

The evolution of the Earth's climate over geological time is now relatively well known. Conversely, the causes and feedback mechanisms involved in these climatic changes are still not well determined. At geological timescales, two factors play a prevailing role: plate tectonics and the chemical composition of the atmosphere. Their climatic effects will be examined using palaeoclimatic indicators as well as results of climate models. I focus primarily on the influence of continental drift on warm and cold climatic episodes. The consequences of peculiar land sea distributions (amalgamation/dispersal of continental blocks) are discussed. Plate tectonics also drive sea level changes as well as mountain uplift. Marine transgressions during the Mid-Cretaceous favoured warmth within the interiors of continents, although their effect could be very different according to the season. Mountain uplift is also an important factor, which is able to alter climate at large spatial scales. Experiments relative to climatic sensitivity to the elevation of the Appalachians during the Late Permian are discussed. To affect the whole Earth, the chemical composition of the atmosphere appears to be a more efficient forcing factor. The carbon dioxide driven by the long-term carbon cycle has influenced the global climate. Geochemical modelling simulates more or less accurately the long-term evolution of pCO₂, which corresponds roughly to the icehouse/greenhouse climatic oscillations. However, the uncertainties on pCO₂ are still important because different parameters involved in the long-term carbon cycle (degassing rate, chemical weathering of silicates, burial of organic matter) are not well constrained throughout the past. The chemical composition of the atmosphere is also altered by the emissions of modern volcanic eruptions leading to weak global cooling. The influence of large flood basalt provinces on climate is not yet known well enough; this volcanism may have released huge amounts of SO₂ as well as CO₂. At last, the chemical composition of the atmosphere may have been altered by the release of methane in response to the dissociation of gas hydrates. This scenario has been proposed to explain the abrupt warming during the Late Palaeocene.     

Sea-level changes and their causes

Book reviewed in this article:
Nils-Axel Morner (ed.): Earth Rheology, Isostasy and Eustasy     

渤海湾西侧泥质海岸带全新世岸线的变化与海洋的影响(英文)

以渤海湾泥质海岸带为例,从形态和地层证据2个方面总结了全新世岸线变化与海洋作用对该地区海岸带发育的影响。中全新世以来千年级别的岸线变迁至少以6次停顿(形成贝壳堤和泥质岭地)和岸进的交替为特征。过去130年间10年级别的岸线变化分为4个阶段,显示了"小冰期"结束后随气温上升而发生的岸线自然蚀退是如何逐渐被人类活动(特别是2000年以来的围海造陆)所取代的。全新世海相沉积中发现的9个峰值期和晚全新世的7次风暴驱动事件,表明了研究区泥质海岸带增强的海洋影响。这些结果提供了一条经由地质背景认识现代泥质海岸带过程的途径。     

Sea-level changes,facies changes and the late Precambrian—Early cambrian evolutionary explosion

An explosive increase in the fossil record coincided with a major rise in sea level during latest Precambrian—early Cambrian times. The artefactual and real effects of an onshore—offshore environmental gradient upon taxonomic diversity are considered, with particular reference to 14 fossiliferous sections from around the world. Within-taxon and within-habitat evolution through the early Cambrian are also discussed. The evidence suggests that evolution was a diversity-dependent (i.e. kinetic) growth process, made possible by the colonisation and gradual filling of habitats that were growing both in variety and area. Archaeocyatha diversified rapidly at first but may have suffered later decline and extinction because facies changes in late early Cambrian times reduced their area of habitat.     

Global climatic changes

Book reviewed in this article:
Berger, A. (ed.): Climatic Variations and Variability: Fits and Thfonrs     

Ice-core records of global climate and environment changes

Precipitation accumulating on the Greenland and Antarctic ice sheets records several key parameters (temperature, accumulation, composition of atmospheric gases and aerosols) of primary interest for documenting the past global environment over recent climatic cycles and the chemistry of the preindustrial atmosphere. Several deep ice cores from Antarctica and Greenland have been studied over the last fifteen years. In both hemispheres, temperature records (based on stable isotope measurements in water) show the succession of glacial and interglacial periods. However, detailed features of the climatic stages are not identical in Antarctica and in Greenland. A tight link between global climate and greenhouse gas concentrations was discovered, CO₂ and CH₄ concentrations being lower in glacial conditions by about 80 and 0.3 ppmv, respectively, with respect to their pre-industrial levels of 280 and 0.65 ppmv. Coldest stages are also characterized by higher sea-salt and crustal aerosol concentrations. In Greenland, contrary to Antarctica, ice-age ice is alkaline. Gas-derived aerosol (in particular, sulfate) concentrations are generally higher for glacial periods, but not similar in both the hemispheres. Marine and continental biomass-related species are significant in Antarctica and Greenland ice, respectively. Finally, the growing impact of anthropogenic activities on the atmospheric composition is well recorded in both polar regions for long-lived compounds (in particular greenhouse gases), but mostly in Greenland for short-lived pollutants.     

Chemical reactions and porosity changes during sedimentary diagenesis

It is of interest to simulate the porosity changes associated with fluid flow and water–rock reactions in sedimentary systems. The chemical species taken into account are: {H₂O, H⁺, Ca⁺⁺, HCO₃⁻, Mg⁺⁺, Al(OH)₄⁻, H₄SiO₄, K⁺, Na⁺, Cl⁻}. The solution is assumed to be locally at equilibrium with different mineral assemblages including at least calcite, dolomite and one Mg–Al-silicate. These assemblages buffer the partial pressure of CO₂ (Pco₂ ) which increases with temperature (T) as is commonly observed in natural systems. The nature of the Mg–Al-silicate and the presence or absence of other at-equilibrium minerals (i.e. the feldspars) do not modify the Pco₂–T relationship. Considering complete transfer between the solution and the solid phases, computed relative porosity increases with increasing temperature for all the systems that were investigated. However, the direction and the amount of the clay transfer depend on the presence of feldspars. Furthermore, it is shown that computing mass transfer using a prescribed Pco₂, as is commonly done, leads to very different values of mineral transfers. Hence, it must be concluded that prescribing a Pco₂ value, even if the proper Pco₂–T relationship is used, leads to erroneous results.     

浅析新生代气候变化与大气温室气体浓度的关系

摘要：根据国内外相关研究结果,对新生代气候变化与温室气体(特别是CO2)浓度在不同时间尺度上的可能关系进行初步归纳和探讨。在构造、轨道和千年时间尺度上,气候变化和温室气体浓度均有显著的相关性,表明温室气体无疑是影响地球气候系统的重要因素。同时,两者亦具有显著的“非耦合”特征,包括新近纪构造尺度上CO2相对稳定水平下的全球变冷和冰量扩张、轨道和千年尺度上CO2浓度变化滞后于气候变化、两半球气候的不对称演化等;两者变化的幅度、趋势和变率也常有不同。这些特征中的多数并不能用地球轨道参数的变化来直接解释,表明除太阳辐射和温室气体外,气候系统内部的其他一些因素或过程有时对过去的气候变化起到了决定性的作用。气候变化与温室气体浓度之间可能存在一种自调节功能,构成一个自调节系统而相互调控,而目前我们对这类过程与机理所知尚少。CO2、CH4等作为温室气体,在上述不同时间尺度的气候变化过程中,无疑对气温具正反馈效应。地质尺度上气候变化与温室气体浓度的关系与机理有助于理解当前全球增温的机制,但把过去与现在类比的同时,也要考虑其他边界条件的不同。加强气候模拟与记录对比的研究,对理解上述问题有望发挥重要作用。 关键词：新生代气候;温室气体;碳循环;人类活动     

Ben Nevis and geologically driven changes in elevation

With a great deal of fanfare in March 2016 an Ordnance Survey press release announced 1345 m as the newly rounded height for Ben Nevis, the highest mountain in Scotland. After a series of complex calculations and surveying, new measurements underpinned by geophysical data revealed that the highest point in the United Kingdom had gone up to by only a few cm since 1949, when it was last measured. This time they were able to use GPS readings from satellites maintained by the US military to pin this down to millimetre precision. The height rose to 1344.527 metres (or 4411 feet and 1½ inches), but Britain's national mapping agency does not reveal exactly what the old height was. Oddly the seventh series 1: 63 360 map (Sheet 47‐Glencoe) published in 1960 was still using 4406 feet, 1343 m. This antiquated height was transferred from the 4406.3 ft inscribed on the six‐inch 1 : 10 560 (Inverness‐shire—Mainland sheet CLI) map published in 1902, relative to the Liverpool datum originally used by the Ordnance Survey. This was probably the base of the cairn upon which the triangulation pillar is built, and not even the nearby summit of Ben Nevis itself. Indeed the OS explains in a video on its website why modern 1 : 50 000 editions show two heights, with brackets around that for the natural high point, to make this distinction clear.     

沉积记录与白垩纪地球表层系统变化

地球表层系统是由岩石圈、大气圈、水圈和生物圈相互耦合和变化组成的复杂巨系统。白垩纪是地球表层系统研究的典范,在地球表层各圈层发生了众多重大地质事件。晚白垩世巨大的地幔热异常引起海底扩张速度变快,导致大量海底高原和海山的形成;同时,冈瓦纳大陆裂解,南北大西洋贯通,新的大洋水道形成,可能造成大洋环流格局的大变化。洋壳体积的增加可能使白垩纪海平面比现在高出200~300 m,大规模海侵也在晚白垩世中期达到最大范围。在这个过程中,火山作用释放出来的营养物质和火山气体的反馈作用造成的大量陆地营养物质的流入共同促使大洋水体富营养化和普遍缺氧,造成“大洋缺氧事件”。CO2浓度的升高（为现今的4~10倍）是火山排气作用的直接结果,其“温室效应”也被认为可能是促成白垩纪大气和海水高温的重要原因（高于现在10 ℃）。大洋红层（CORB）是最新提出并被广泛接受的白垩纪重要地质事件,被定义为一套分布在从外陆棚到CCD面之下深水盆地的,在富氧、低生产力和贫营养条件下较低速沉积形成的品红-红色-棕色的细粒远洋沉积物。这些发生于地球表层各圈层的重大地质事件以能量循环的方式（具体表现为C、S、P、H、O等元素循环）相互耦合和变化共同支撑着地球表层系统的运转。但是科学界对这些重大地质事件的成因机制及其所引起的全球变化性质还没有形成一致意见,原因之一就是缺乏对陆相沉积记录的研究。陆相白垩系的广泛发育和“松辽盆地白垩系科学钻探”工程的顺利实施共同构成了中国在白垩纪地球表层系统研究上的地域和材料优势,结合中国在白垩纪地球表层系统重大地质事件研究中已经形成的学术优势,从地球系统科学的角度出发,通过多学科交叉研究将是解决以上问题的关键。     

1973—2020年阿尔金山冰川面积变化及其对气温变化的响应

研究冰川面积变化对气温变化的响应模式,对于冰川资源的保护和利用具有重要意义。利用Landsat MSS、TM和OLI影像,采用比值阈值法结合目视修正,提取了阿尔金山地区1973—2020年8个时期的冰川边界信息,分析了冰川的时空变化特征,并结合距离阿尔金山较近的且末、若羌、茫崖和冷湖等四个气象站点的气象数据,分析了冰川变化对气温变化的响应规律。主要结论如下：1973—2020年阿尔金山地区冰川整体处于退缩状态,面积减少了（64.89±12.36） km²（19.21%±2.90%）;1973—1990年冰川退缩较快,年均退缩率为（0.49±0.07）%·a^-1;1990—1995年和1995—2000年这两个时期冰川退缩最快,年均退缩率分别为（1.07±0.08）%·a^-1和（1.08±0.08）%·a^-1;2000年后,冰川退缩速率较慢,比较稳定,年均退缩率均低于0.2%·a^-1。气温是影响阿尔金山地区1973—2020年冰川变化的主要气候因子。阿尔金山地区冰川对不同气温变化阶段的响应模式为：气温升高阶段,冰川消融,冰川面积减少;气温稳定阶段,冰川逐渐进入新的动态均衡状态,冰川面积也相对稳定;气温降低阶段,因冰川运动的滞后性,冰川面积在短时间内无明显变化。     

Climatic changes in Bahrain

Local and regional studies of climatic patterns confirm that temperatures are rising in the Arabian Gulf area. Further warming of the region, which is already unbearably hot is an environmental catastrophe on a new scale. It has potential to violently disrupt virtually every natural ecosystem and many of the structures and institutions that people depend on. It seems that the Arabian Gulf region is also a part of global warming or the green house effect. This paper analyzes temperatures, rainfall, humidity, sunshine, evaporation and wind speeds. The effect of the Gulf War or Desert Storm has also been included. The study confirms that temperature is rising at a rate of 1.4°C in 100 years. In the beginning a brief discussion of geography, culture, water resources and modern development in Bahrain is given to introduce the country.     

Flandrian sea-level changes in the Fenland. I: The geographical setting and evidence of relative sea-level changes

The Flandrian sediments of the Fenland record the infilling of the Wash embayment on the east coast of England, UK. Since at least 6500 BP changes in sea level have been a major control on the rate and pattern of sediment accumulation. New data are presented from the area which together with published information allow the reconstruction of palaeoenvironments from 6500 to 2500 BP. The major environmental changes involved alternations between freshwater fen and intertidal marine sedimentation. Each episode was characterised by transitional changes as vegetation and sediment zones shifted over large areas. Marine/brackish sediments are found up to 45 km inland of the present coast. Radiocarbon dated sea-level index points, with relevant stratigraphic and micropalaeontological data, ranging from 6415 BP at ?8.17m OD to 2595 BP at +1.45m OD, are described.