末次冰盛期和全新世中期东亚地区水汽输送的模拟研究

利用国际古气候模拟比较计划最新第3阶段中9个气候模式针对末次冰盛期、13个气候模式针对全新世中期的数值试验数据,集中研究了这两个时期东亚地区的水汽输送变化。结果表明,相对于工业革命前期,末次冰盛期东亚地区冬季异常水汽输送主要来自跨赤道气流和西北太平洋,东亚大陆沿岸及其临近海域为主要的水汽异常辐合区,对应冬季净降水量增加,异常辐散区主要位于热带海洋和西北太平洋,净降水量减少;夏季,东亚地区异常水汽输送通量以辐散为主,大部分地区净降水量减少,对应东亚夏季风减弱。全新世中期东亚地区冬季水汽输送变化较弱,东南部及临近海域和赤道中太平洋为异常辐散区,不利于冬季净降水;夏季异常水汽输送分别来自热带中西太平洋广阔洋面和西北太平洋异常反气旋式环流西南侧,东亚大陆大部分地区为水汽异常辐合区,夏季净降水量增加,对应东亚夏季风增强。两个时期外强迫驱动下的经向温度梯度、海陆热力对比和大气含水量变化是上述冬、夏季东亚水汽输送异常的主因。

     

末次冰盛期与全新世青藏高原松属植被分布及其演变

史前人类与其生存环境,特别是与植被之间的相互作用一直是人们关注的焦点。气候变化与人类活动对植被覆盖格局的塑造均有重要影响,厘清植被分布及其植被变化背后的气候或人为因素,有助于更好地认识人类活动对植被环境的影响程度与范围。本研究对青藏高原松属（Pinus spp.）植被适生区分布动态历史进行了物种分布模型模拟,并结合环境考古学、古生态学等多学科方法,探究青藏高原松属植被分布变化历史及其驱动因素。结果表明,基于最大熵（MaxEnt）算法并结合R语言包ENMeval来优化参数设置的模型性能表现良好且稳健,较为准确模拟松属在青藏高原地区不同时期的适生区分布动态。高原上松属适生区在末次冰盛期（LGM）分布最小,仅在东缘的河谷局地;在全新世早、中期分布达到最大值,到全新世晚期部分区域分布缩小,高原东北部高度适生区向2500 m a. s. l.上下的低海拔谷地收缩,整体上与高原气候变化趋势大体一致。结合化石花粉、木炭等证据表明,全新世中晚期以前,人类对高原松属植被影响总体尚不显著;进入全新世晚期,农业技术的进步促使高原东北部人口快速增加,高原上现已发现的古遗址也高度集中在此。结合多项考古证据表明,人类对松属为代表的林木资源规模化开发行为开始显著干扰了当地植被,人类对松属等针叶林木材资源的利用可能是该地区树种向阔叶林树种演替的重要驱动因素之一。

     

NAO在末次冰盛期和全新世对AMOC影响的对比研究

大西洋经向翻转环流(AMOC)的年代际变率对气候变化起着重要的调制作用。在现代气候背景下, 北大西洋涛动(NAO)加强能使AMOC增强, 但这种关系在更长时间尺度上是否成立尚不清楚。本研究利用TraCE-21ka模拟资料, 对比分析末次冰盛期(LGM)和全新世时期NAO对AMOC影响的异同。结果表明, LGM时期较全新世时期经向温度梯度偏强, NAO位置偏南, 这导致NAO与AMOC关系的不同: NAO的增强在LGM时期可以使AMOC增强, 而在全新世使AMOC减弱。具体地, 在LGM时期NAO的加强使北大西洋副极地气旋性环流增强, 其南支导致向北的高盐海水输送增加, 从而使北大西洋副极地区域密度升高, AMOC增强。与此同时, NAO正位相还能在中纬度激发异常的Ekman下沉流使AMOC加强。相反, 在全新世时期, NAO正位相导致北大西洋副极地地区气旋性环流减弱, 这导致中纬度向高纬度输送的高盐度海水减少, AMOC减弱。本研究表明NAO与AMOC的关系在很大程度上取决于不同气候背景下NAO的位置。

     

从末次冰盛期冰川规模探讨当时的气候环境

根据乌鲁木齐河源区末次冰盛期形成的保存完好的古冰川遗迹和现代气候条件下冰川特平衡与气候的关系。用冰川动力学方法估算出冰川达到末次冰盛期规模时的气候条件。依据末次冰盛期冰川面积，结合冰川平衡线高度和冰川体积综合分析，乌鲁木齐河源区末次冰盛期的夏季气温应比现代低４．８℃左右，降水约只有现代的３０％，但目前其它古气候方法的研究结果表明，末次冰盛期的夏季气温比现代低５．６℃左右，两者相差０．８℃，其原因可     

从末次冰盛期冰川规模探讨当时的气候环境——以乌鲁木齐河源区末次冰盛期冰川为例

根据乌鲁木齐河源区末次冰盛期形成的保存完好的古冰川遗迹和现代气候条件下冰川物质平衡与气候的关系，用冰川动力学方法估算出冰川达到末次冰盛期规模时的气候条件。依据末次冰盛期冰川面积，结合冰川平衡线高度和冰川体积综合分析，乌鲁木齐河源区末次冰盛期的夏季气温应比现代低４．８℃左右，降水约只有现代的３０％。但目前其它古气候方法的研究结果表明，末次冰盛期的夏季气温比现代低５．６℃左右，两者相差０．８℃，其原因可能主要是冰川动力学方法未考虑构造抬升对气温的影响，据此推测，乌鲁木齐河源区末次冰盛期至今的构造上升量约为１３０ｍ。     

末次冰盛期气候反馈特征研究

末次冰盛期（Last Glacial Maximum,简称LGM）被认为是较适合用来估算气候系统响应对辐射强迫变化的古气候区间之一。理解LGM时期气候反馈过程有助于进一步限定气候敏感度的范围。本研究利用辐射核方法和参加第三次古气候模式比较计划（Paleoclimate Modelling Intercomparison Project Phase Ⅲ,简称PMIP3）的8个耦合模式资料,对比研究了LGM时期与abrupt4xCO₂（4CO₂）情景下的气候反馈特征。结果表明：全球平均而言,不同情景下温度反馈、水汽反馈和反照率反馈的强度存在显著差异,然而这一关系并不存在于云反馈过程中,这可能与情景间/模式间云反馈的不确定性相联系;在不同情景下,不同反馈过程强度也存在明显空间差异。温度反馈过程的差异主要来源于LGM时期大陆冰盖强迫引起的温度变化的高度空间不均一性和海陆分布改变引起的热带对流活动的变化;水汽反馈变化可能与海陆分布变化引起的沃克环流变化以及全球降温相联系;大陆冰盖和海冰存在是导致LGM时期地表反照率反馈增加的主要原因;而云反馈的差异可能与低云云量和模式间不确定性有关。LGM时期单独强迫数值试验将有助于进一步厘清不同气候状态下气候反馈过程差异的原因。

     

末次冰盛期黑潮变化的数值模拟

黑潮是北太平洋西部边界流, 能够携带西太平洋暖池热量向北输送, 影响中国海的水文循环及全球气候。本研究利用高分辨率区域海洋模式(ROMS), 模拟了现代及末次冰盛期(LGM)黑潮流量和流轴的三维结构。气候态分析再现了现代黑潮的流量, 在PCM-1阵列、PN测线和吐噶喇海峡的流量分别是23.8 Sv、28.0 Sv和28.2 Sv, 与观测结果接近。LGM模拟中以上3个断面流量分别为34.5 Sv、34.4 Sv和34.9 Sv, 流量明显增加。垂直结构显示末次冰盛期(LGM)时期黑潮主轴仍位于冲绳海槽内, 深度范围也比现代大。LGM时期黑潮进入冲绳海槽前受到海槛阻挡, 部分黑潮流向发生偏转, 使得琉球海流加强。LGM时期黑潮加强主要受副热带环流圈信风加强和风应力旋度减小造成的Sverdrup输送加强控制。黑潮上游北赤道流加强, 导致向北输送流量增加。研究结果可以帮助认识黑潮在全球水循环的重要作用。

     

末次冰盛期以来冲绳海槽古海洋环境研究进展

冲绳海槽处于东海与西太平洋边缘的交界处,不仅对全球气候变化响应敏感,其环境变化也影响着东亚边缘海,乃至东亚大陆的环境,是研究古海洋环境的理想区域。该区域的古海洋环境研究多集中于末次冰盛期以来,因此本文以冲绳海槽为主体,总结了该区域末次冰盛期以来古海洋环境变化的相关研究,主要包括3个方面：古海平面、温度和盐度等;沉积物来源及其演化;黑潮及其对海洋环境的影响。该区域末次冰盛期以来的环境变化可大致分为,主要由海平面控制为主的末次冰盛期-早全新世和由黑潮、季风等因素控制的早全新世-现代两个主要的阶段。沉积物主要来自古黄河、长江、日本、台湾岛以及火山喷发物质等,但不同区域、不同时间的物质来源存在差异。另外,黑潮是该区域最主要的海流,其路径和强度末次冰盛期以来经历多次变化,并对其他海洋环境要素产生重大的影响。综合上述研究,提出未来应该系统建立冲绳海槽海洋环境演化历史、加强黑潮对周边流系的影响和陆源物质源-汇过程的系统研究。

     

中国末次冰盛期以来泥炭发育与气候变化

泥炭是陆地生态系统碳库的重要组成部分,其发育演化对全球碳循环具有重要的影响。然而,目前轨道时间尺度上中低纬泥炭发育与季风演化关系及其对全球CH₄浓度变化的影响,还存在很大的争议。本研究基于末次冰盛期以来我国泥炭发育的起始¹⁴C年龄数据,通过年龄概率密度方法,系统重建了东亚季风区泥炭发育的时空演变历史。结果表明：末次冰盛期我国南方泥炭开始发育,冰消期以来泥炭发育逐步扩展至华北、东北、西北和青藏高原地区,并发育增强;全新世时段,不同区域泥炭发育存在明显的空间差异,东北和西北泥炭发育呈现持续增加,而南方、华北和青藏高原地区在早-中全新世增加,之后呈现下降趋势。结合全国孢粉记录的古气候定量化重建结果,发现我国末次冰盛期以来不同区域泥炭发育主要受降水变化的影响,揭示出泥炭发育主要受控于东亚季风降水的演化。研究表明在轨道时间尺度上,东亚季风演化及其导致的泥炭发育变化对全球CH₄浓度变化具有重要的贡献。

     

黄河上游末次冰盛期古洪水事件的初步研究

洪水的发生规律是洪灾预报的前提，已有的人类洪水记录时间尺度，不足以认识和把握洪水的出现规律。因此，利用地质记录延长洪水序列，探讨地球特征气候期的洪水特点，就显得非常重要的必要。黄河上游兰州－银川段的洪水地质记录表明，在末次冰盛期的20－18ka，该区共发生了106次大洪水漫滩事件，其中有18次为多次洪峰叠加的复合型大洪水，洪水的发生频率达53次/ka。发生于末次冰盛期的大洪水可能属冰凌洪水，与末次冰盛期强烈的气候波动和不稳定有关。这些大洪水的频发与中国西部的末次冰盛期出现的高湖面相对应，既不符合一般的季风气候理论，也不同于我国东部广大地区末次冰盛期以冷干为主的气候特点，表明中国西部气候的独特性和复杂性。     

青藏高原东部末次冰期最盛期气候的花粉证据

青藏高原许多湖泊钻孔、泥炭剖面等所揭示的花粉记录为重建当时的古气候提供了可靠的证据．应用这些资料探讨青藏高原东部末次最大盛冰期植被和气候．大约２５～１５ｋａＢＰ前后西藏东南部、川西若尔盖及青海柴达木和可可西里地区,气候寒冷干燥,年均气温比现今低６℃左右,植被以荒漠草原为主;在青海湖地区森林退缩演变为草原植被;甘肃临夏气候冷湿,年均温比现在低５～６℃,发育山地暗针叶林     

印度尼西亚多岛海末次冰期最盛期以来的穿越流活动

印度尼西亚穿越流是西太平洋和印度洋之间热量传输的重要载体,穿越流的活动由潜在地影响El Nino和季风现象进而影响到全球气候变化。通过对爪哇海SHI9006岩心LGM以来氧同位素、有孔虫与CaCO3沉积量、浮游有孔虫浅层水种与深层水种比值反映的古温跃层变化等的研究,得出结论：研究区末次冰期氧同位素2期穿越流活动微弱,冰后期穿越流活动增强;特别是冰消期终止期IA,穿越流活动由弱迅速增强,是冰川消融、海平面上升,印度尼西亚岛弧古海水通道开放的结果。     

Last Glacial Maximum and Hypsithermal in the Southern Hemisphere

A synthesis of the two contrasting climates of the upper Quaternary in the Southern Hemisphere, based on continental geological indicators, suggests that the Antarctic Anticyclone is the most important climatic system in the hemisphere. According to glaciological and oceanographic studies, the Antarctic Anticyclone covered an area in the LGM that was double of that during the Hypsithermal. This phenomenon produced a consequent shifting of the climatic belts by approximately 10° of latitude to the north in the LGM and a migration to the south during the Hypsithermal. Oceanic and continental anticyclones were active systems in shaping climates in South America, Australasia, and Southern Africa. These structures were enhanced throughout the LGM (provoking generalized droughts), and weakened at the Hypsithermal (permitting more rains in tropical latitudes). The results presented here were obtained by integrating our own results with regional and continental syntheses of other authors. The paleoclimatic proposals are amply validated by more than 1500 dates in the four continents. Geological and geomorphological features, such as dunefields, paleosols, fluvial terraces and lake levels were the main tools employed in the work.     

末次盛冰期以来青藏高原东北部共和盆地气候与环境变化研究进展

青藏高原东北部共和盆地气候与环境变化文献分析认为:末次盛冰期(14 C年龄14ka BP或16cal ka BP之前)地层沉积主要为风成砂和黄土,冰缘地貌发育,气候寒冷干燥,植被可能为干旱荒漠或荒漠草原;末次冰消期(14 C年龄14ka BP或16 cal ka BP-Younger Dryas,缩写YD事件)地层发育古土壤,湖泊水位明显上升,并显著的捕捉到冷暖事件(Blling-Allerd,缩写B/A、YD)的信息,气候趋于温暖湿润,对应植被为荒漠草原;全新世8.5ka BP(14 C年龄)之前区域温度和湿度不同程度增加,湖泊水位较高,地层发育古土壤,植被为荒漠草原或干草原;8.5～7.0ka BP(14 C年龄)风成砂出现,古土壤发育中断,气候寒冷干燥,为全新世新冰期第一期;7.0～3.0ka BP(14 C年龄)古土壤显著发育,高水位湖面出现,水热组合达到全新世最佳,植被向干草原方向演化,但期间也存在千–百年尺度的冷事件(全新世新冰期第二期);3.0ka BP(14 C年龄)以来气候向温凉(寒冷)干燥方向发展.太阳辐射等外部因素变化并触发地球系统内部各个圈层之间相互作用是区域气候、环境变化的主要驱动力.同时,对研究现状进一步剖析,阐明其存在的问题,并提出气候、环境变化研究的发展方向.     

Climate variability during the Last Glacial Maximum in eastern Australia: evidence of two stadials?

A high‐resolution, multiproxy record encompassing the last glacial–interglacial transition is presented for Native Companion Lagoon, a coastal site in subtropical eastern Australia. Rates of aeolian sedimentation in the lake were established by trace element analyses of lacustrine sediments and used as a proxy for aridity. In conjunction with sediment moisture content, charcoal and pollen these provide a multi‐decadal record of palaeoenvironmental variability for the period 33–18 k cal. yr BP. Results indicate that the Last Glacial Maximum in eastern Australia spanned almost 10 k cal. yr, and was characterised by two distinct cold dry events at approximately 30.8 k cal. yr BP and 21.7 k cal. yr BP. Provenance of selected sediment samples by trace element geochemical fingerprinting shows that continental sourced aeolian sediments originated primarily from South Australia during these cold events and from sites in central Australia during the intervening time. Used in combination with a pollen record, the provenance of long‐travelled dust to mainland sites shows that the two cold events were characterised by frequent meridional dry southwesterly winds rather than zonal westerly airflow as previously believed. The intervening period was cool and humid, which we infer as being associated with more frequent southeasterly winds of maritime origin. These results lend support to previous research that indicates the Southern Hemisphere experienced a period of widespread climatic amelioration at the height of the last glacial known as the Antarctic Isotopic Maximum. Copyright © 2008 John Wiley & Sons, Ltd.     

Climatic Instability Study of Lanzhou since Last Glacial Maximum

INTRODUCTIONA great number of records from ice cores andocean sediments ( Bond et al., 1993; Dansgaard etal., 1993; Grootes, et al., 1993 ) reveal that theearth has experienced an integrated cool warm cli matic cycle since the LGM, in the course of which aseries of rapid and high amplitude oscillations oc curred (Chondrogianni et al., 2004). These impor tant oscillations, known as Heinrich events, Youn ger Dryas event and last deglaciation, initia…     

Fast-flowing outlet glaciers of the Last Glacial Maximum Patagonian Icefield

Glacial geomorphology around the Northern Patagonian Icefield indicates that a number of fast-flowing outlet glaciers (the continuation of ice streams further upglacier) drained the icefield during the Last Glacial Maximum. These topographically controlled fast-flowing glaciers may have dictated the overall pattern of Last Glacial Maximum ice discharge, lowered the ice-surface profile, and forced the ice-divide westward. The influence of the fast-flowing outlet glaciers on icefield behavior also helps to explain why the configuration of the Patagonian Icefield at the Last Glacial Maximum is not accurately represented in existing numerical ice-sheet models. Fast-flowing outlet glaciers would have strongly influenced ice discharge patterns and therefore partially decoupled the icefield from climatically induced changes in thickness and extent.     

Coastal Ocean Last Glacial Maximum to 2100 CO2-Carbonic Acid-Carbonate System: A Modeling Approach

Using coupled terrestrial and coastal zone models, we investigated the impacts of deglaciation and anthropogenic inputs on the CO₂–H₂O–CaCO₃ system in global coastal ocean waters from the Last Glacial Maximum (LGM: 18,000 year BP) to the year 2100. With rising sea level and atmospheric CO₂, the carbonate system of coastal ocean water changed significantly. We find that 6 × 10¹² metric tons of carbon were emitted from the coastal ocean, growing due to the sea level rise, from the LGM to late preindustrial time (1700 AD) because of net heterotrophy and calcification processes. This carbon came to reside in the atmosphere and in the growing vegetation on land and in uptake of atmospheric CO₂ through the weathering of rocks on land. It appears that carbonate accumulation, mainly, but not exclusively, in coral reefs from the LGM to late preindustrial time could account for about 24 ppmv of the 100 ppmv rise in atmospheric CO₂, lending some support to the “coral reef hypothesis”. In addition, the global coastal ocean is now, or soon will be, a sink of atmospheric CO₂. The temperature rise of 4–5°C since the LGM led to increased weathering rates of inorganic and organic materials on land and enhanced riverine fluxes of total C, N, and P to the coastal ocean of 68%, 108%, and 97%, respectively, from the LGM to late preindustrial time. During the Anthropocene, these trends have been exacerbated owing to rising atmospheric CO₂, due to fossil fuel combustion and land-use practices, other human activities, and rising global temperatures. River fluxes of total reactive C, N, and P are projected to increase from late preindustrial time to the year 2100 by 150%, 380%, and 257%, respectively, modifying significantly the behavior of these element cycles in the coastal ocean, particularly in proximal environments. Despite the fact that the global shoal water carbonate mass has grown extensively since the LGM, the pH_T (pH values on the total proton scale) of global coastal waters has decreased from ~8.35 to ~8.18 and the carbonate ion concentration declined by ~19% from the LGM to late preindustrial time. The latter represents a rate of decline of about 0.028 μmol CO₃ ^2? per decade. In comparison, the decrease in coastal water pH_T from the year 1900 to 2000 was about 8.18–8.08 and is projected to decrease further from about 8.08 to 7.85 between 2000 and 2100, according to the IS92a business-as-usual scenario of CO₂ emissions. Over these 200 years, the carbonate ion concentration will fall by ~120 μmol kg^?1 or 6 μmol kg^?1 per decade. This decadal rate of decline of the carbonate ion concentration in the Anthropocene is 214 times the average rate of decline for the entire Holocene. Hence, when viewed against the millennial to several millennial timescale of geologic change in the coastal ocean marine carbon system, one can easily appreciate why ocean acidification is the “other CO₂ problem”.