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1.
在国际古气候模拟比较计划设置的标准试验方案下,首先利用中国科学院大气物理研究所的全球大气环流模式（IAP-AGCM）模拟了末次盛冰期东亚气候状况,然后通过4组数值敏感性试验逐一模拟了大气CO2浓度、海洋表面温度（SST）和海冰、陆地冰盖和地形、东亚植被变化4项强迫因子的单独气候效应,进而对末次盛冰期东亚气候的成因进行了检测。结果表明,末次盛冰期除华南局部略有升温外,中国年均地表气温显著降低,降温幅度总体上向北增大,青藏高原处存在一个降温中心。其中,SST和海冰变化是华南局部略偏暖的主因,它同时导致了东亚其他区域地表气温的显著降低,特别是在东北亚地区;陆地冰盖和地形变化对于东亚地表气温的显著冷却作用主要体现在东亚的西北部;大气CO2浓度降低会引起东亚地区0.2～0.9℃的普遍降温;相对而言,东亚植被的降温作用（0.5～1.0℃）主要显现在中国40°N以南的区域。与此同时,SST和海冰变化能引起中国东部年均降水一定程度的减少,而大气CO2浓度、陆地冰盖和地形、东亚植被单独变化均不会显著影响东亚年均降水的分布状况,然而,上述四项因子的共同变化会通过协同作用引起中国东部年均降水的显著减少,西部地区降水则与现在差别不大。此外,末次盛冰期东亚夏季风的显著减弱源于SST和海冰变化,冬季风变化则可归因于SST和海冰、陆地冰盖和地形的变化。 相似文献
2.
The role of megatides and relative sea level in controlling the deglaciation of the British–Irish and Fennoscandian ice sheets 
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下载免费PDF全文 Key external forcing factors have been proposed to explain the collapse of ice sheets, including atmospheric and ocean temperatures, subglacial topography, relative sea level and tidal amplitudes. For past ice sheets it has not hitherto been possible to separate relative sea level and tidal amplitudes from the other controls to analyse their influence on deglaciation style and rate. Here we isolate the relative sea level and tidal amplitude controls on key ice stream sectors of the last British–Irish and Fennoscandian ice sheets using published glacial isostatic adjustment models, combined with a new and previously published palaeotidal models for the NE Atlantic since the Last Glacial Maximum (22 ka BP). Relative sea level and tidal amplitude data are combined into a sea surface elevation index for each ice stream sector demonstrating that these controls were potentially important drivers of deglaciation in the western British Irish Ice Sheet ice stream sectors. In contrast, the Norwegian Channel Ice Stream was characterized by falling relative sea level and small tidal amplitudes during most of the deglaciation. As these simulations provide a basis for observational field testing we propose a means of identifying the significance of sea level and tidal amplitudes in ice sheet collapse. 相似文献
3.
大洋环流型式转换在冰期旋回中的作用及经典第四纪冰期理论质疑(续)汉景泰Ｗ．Ｓ．Ｆｙｆｅ(加拿大西安大略大学地质系)４问题及讨论大洋环流－气候学说认为从冰期到间冰期海洋－大气系统全球性巨型再组合导致了末次冰期的终止。 相似文献
4.
The Late Quaternary sediment sequence of the continental margin in the eastern Weddell Sea is well suited for palaeoenvironmental reconstructions. Two cores from the upper slope, which contain the sedimentary record of the last 300 ky, have been sedimentologically investigated. Age models are based on lithostratigraphy and are correlated with the stable isotope record. As a result of a detailed analysis of the clay mineral composition, grain size distributions and structures, this sedimentary record provides the first marine evidence that the Antarctic ice sheet extended to the shelf edge during the last glacial.The variations in volume and size of the ice sheet were also simulated in numerical models. Changes in accumulation rate and ice temperature are of some importance, but the model revealed that fluctuations are primarily driven by changes in eustatic sea-level and that the ice edge extended to the shelf edge during the last glacial maximum. This causal relationship implies that the maximum ice extension strongly depends on the magnitude and duration of the sea-level depression during a glacial period. The results of the sedimentological investigations and of the numerical models show that the Antarctic ice sheet follows glacial events in the northern hemisphere by teleconnections of sea level.
Correspondence to: H. Grobe 相似文献
5.
The GISP2, central Greealand, glaciochemical series (sodium, potassium, ammonium,calcium, magnesium, sulfate, nitrate and chloride) provides a unique view of the chemistry of the atmosphere and the history of atmospheric circulation over much of the Northern Hemisphere. Interpretation of this record reveals the controls on both high and low frequency climate events of the last 110 000 years.Changes in insolation on the order of the major orbital cycles control the long-term behavior of atmospheric circulation patterns through changes in ice volume (sea level) and related positive feedbacks.Events such as the Heinrich events (massive discharges of icebergs first identified in the marine record)are found to operate on a 6 100 year cycle due largely to the lagged response of ice sheets to changes in insolation and consequent glacier dynamics Rapid climate change events (massive reorganizations of atmospheric circulation) are demonstrated to operate on 1 450 year cycle possibly in response to internal oscillations in the ocean-atmosphere system or due to changes in solar output. Changes in insolation and associated positive feedbacks related to ice sheets assist in explaining favorable time periods and controls on the amplitude of these massive rapid climate change events.Comparison of the GISP2 glaciochemical series with an ice record from Taylor Dome in Antarctica indicates considerable similarity suggesting that both polar regions experience marked changes in climate. While preliminary evidence points to similar phasing of several major climate events in the two polar regions exact phasing cannot as yet be determined, because dating of Antarctic ice core records is not as well-established as the dating for Greenland ice cores. 相似文献
6.
Heinrich事件和末次冰期气候的不稳定性 总被引：10，自引：0，他引：10
对北大西洋深海沉积物的研究表明：末次冰期北大西洋沉积物记录中有多次洋面温度降低、有孔虫含量减少、盐度降低和粗颗粒的碳酸盐碎屑快速堆积的现象，这些时间跨度上千年或几百年的气候快速波动被称为Heinrich事件［１－４］，很难用古气候的米兰科维奇理论来解释。最近对末次冰期中国马兰黄土堆积的调查发现，在末次冰期之中东亚冬季风也有多次加强，它与北大西洋沉积物中的Heinrich事件对应很好，暗示着东亚季风的变迁更直接受控于北半球冰量的变化，而不是过去人们认为的东亚古季风气候变化与地球轨道变化引起太阳辐射变化直接相关。 相似文献
7.
《Quaternary Science Reviews》1995,14(1):1-16
Direct evidence for Late Weichselian grounded glacier ice over extensive areas of the Barents Sea is based largely on indirect observations, including elevations of old shorelines on Svalbard and arguments of isostatic rebound. Such isostatic models are discussed here for two cases representing maximum and minimum ice-sheet reconstructions. In the former model the ice extends over the Kara Sea, whereas in the latter the ice is limited to the Barents Sea and island archipelagos. Comparisons of predictions with observations from a number of areas, including Spitsbergen, Nordaustlandet, Edgeøya, Kong Karls Land, Franz Josef Land, Novaya Zemlya and Finnmark, support arguments for the existence of a large ice sheet over the region at the time of the last glacial maximum. This ice sheet is likely to have had the following characteristics, conclusions that are independent of assumptions made about the Earth's rheological parameters. (i) The maximum thickness of this ice was about 1500–2000 m with the centre of the load occurring to the south and east of Kong Karls Land. (ii) The ice sheet extended out to the western edge of the continental shelf and its maximum thickness over western Spitsbergen was about 800 m. (iii) To the north of Svalberg and Frans Josef Land the ice sheet extended out to the northern shelf edge. (iv) Retreat of the grounded ice across the southern Barents Sea occurred relatively early such that this region was largely ice free by about 15,000 BP. (v) By 12,000 BP the grounded ice had retreated to the northern archipelagos and was largely gone by 10,000 BP. (vi) The ice sheet may have extended to the Kara Sea but ice thicknesses were only a fraction of those proposed in those reconstructions where the maximum ice thickness is centered on Novaya Zemlya. Models for the palaeobathymetry for the Barents Sea at the time of the last glacial maximum indicate that large parts of the Barents Sea were either very shallow or above sea level, providing the opportunity for ice growth on the emerged plateaux, as well as on the islands, but only towards the end of the period of Fennoscandian ice sheet build-up. 相似文献
8.
This paper reviews the evidence presently available (as at December 2003) for the compilation of the Glacial Map of Britain (see [Clark C.D., Evans D.J.A., Khatwa A., Bradwell T., Jordan C.J., Marsh S.H., Mitchell W.A., Bateman, M.D. , 2004. Map and GIS database of glacial landforms and features related to the last British Ice Sheet. Boreas 33, 359–375] and http://www.shef.ac.uk/geography/staff/clark_chris/britice.html) in an effort to stimulate further research on the last British Ice Sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology. The wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions. Landforms interpreted as being of unequivocal ice-marginal origin (moraines, ice-contact glacifluvial landforms and lateral meltwater channels) and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice-sheet margins throughout the last glacial cycle. Subglacial landforms (drumlins, flutings and eskers) have been used to demarcate former flow patterns within the ice sheet. The compilation of evidence in a regional map is crucial to any future reconstructions of palaeo-ice sheet dynamics and will provide a clearer understanding of ice sheet configuration, ice divide migration and ice thickness and coverage for the British Ice Sheet as it evolved through the last glacial cycle. 相似文献
9.
Dorthe Klitgaard Kristensen Tine L. Rasmussen Nalan Koç 《Boreas: An International Journal of Quaternary Research》2013,42(3):798-813
The sediment core NP05‐71GC, retrieved from 360 m water depth south of Kvitøya, northwestern Barents Sea, was investigated for the distribution of benthic and planktic foraminifera, stable isotopes and sedimentological parameters to reconstruct palaeoceanographic changes and the growth and retreat of the Svalbard–Barents Sea Ice Sheet during the last ～16 000 years. The purpose is to gain better insight into the timing and variability of ocean circulation, climatic changes and ice‐sheet behaviour during the deglaciation and the Holocene. The results show that glaciomarine sedimentation commenced c. 16 000 a BP, indicating that the ice sheet had retreated from its maximum position at the shelf edge around Svalbard before that time. A strong subsurface influx of Atlantic‐derived bottom water occurred from 14 600 a BP during the Bølling and Allerød interstadials and lasted until the onset of the Younger Dryas cooling. In the Younger Dryas cold interval, the sea surface was covered by near‐permanent sea ice. The early Holocene, 11 700–11 000 a BP, was influenced by meltwater, followed by a strong inflow of highly saline and chilled Atlantic Water until c. 8600 a BP. From 8600 to 7600 a BP, faunal and isotopic evidence indicates cooling and a weaker flow of the Atlantic Water followed by a stronger influence of Atlantic Water until c. 6000 a BP. Thereafter, the environment generally deteriorated. Our results imply that (i) the deglaciation occurred earlier in this area than previously thought, and (ii) the Younger Dryas ice sheet was smaller than indicated by previous reconstructions. 相似文献
10.
EILIV LARSEN SVEND FUNDER JÖRN THIEDE 《Boreas: An International Journal of Quaternary Research》1999,28(1):6-11
This synopsis highlights some of the main results presented in this issue of Boreas. The collection of papers deals with ice sheet reconstruction in space and time, isostatic and eustatic response to deglaciation, land to shelf sediment interaction, and Eemian and Holocene environmental variations. The most significant new results are that the last glacial maximum of the Kara Sea and Barents Sea ice sheets were both much smaller and much older than in most previous hypotheses. This puts new constraints on, for example, climate and ice sheet linkages, ice sheet interactions (Scandinavian-Barents Sea-Kara Sea), and land-ocean riverine input through time. 相似文献
11.
利用美国NCAR CAM3大气环流模式,分析了末次盛冰期（LGM）两个不同的热带海表温度重建方案中,北半球冬季热带中、西太平洋对流活动及大气环流对暖池外（赤道东太平洋和热带大西洋）热带SST异常的敏感性。结果表明： 1）SST异常首先引起大气环流的改变。 赤道东太平洋对流层下沉增强,而作为经向补偿,副热带东太平洋上升运动增强,其中南半球尤为明显,同时南半球热带中、西太平洋上升运动增强,加剧了该区纬向逆时针环流,说明冰期热带海气耦合过程受气候背景场（如SST）影响很大; 2）大气环流格局改变引起热带中西太平洋的大气加热、对流活动、表层风场及降雨的巨大变化。 140°E以西的婆罗洲和菲律宾区域,总的大气加热减少是由于对流与辐射加热减少所致,对应于该区风场辐散和降雨减少; 而140°E以东的南半球热带中、西太平洋,大气吸收热量增加,对流与辐射加热均增强,总降雨量也随之增加,反映该区赤道辐合带南移并增强。该项研究为探索热带太平洋在冰期/间冰期旋回中的古海洋学变化提供了新的数据支撑。此外,不同重建SST对赤道辐合带的影响比较大,因此利用重建SST进行数值模拟或者利用耦合模式研究LGM热带海气相互作用时,应该十分重视全球热带SST分布特征。 相似文献
12.
J. Oerlemans 《Quaternary Research》1980,14(3):349-359
The interaction between continential ice sheets and the planetary radiation budget is potentially important in climate-sensitivity studies. A simple ice-sheet model incorporated in an energybalance climate model provides a tool for studying this interaction in a quantitative way. Experiments in which the ice-sheet model is coupled step by step to the climate model show that ice sheets hardly affect the zonal mean radiation balance because the albedo feedback due to sea ice and snow cover is dominating. The model requires a 5% drop in the solar constant to create ice sheets of ice-age size.If the feedback between surface elevation and ice-mass balance is included (in a very crude way), the ice-sheet size (L, measured southward from 70°N) becomes much more sensitive to in insolation. For a range of normalized solar constants, roughly from 0.98 to 1.02, two stable solutions exist: L 0 and L 2000 km. This result demonstrates that the response of ice sheets to insolation variations is far from linear. It also stresses the need for explicit modeling of the ice-mass balance of ice sheets, particularly its dependence on surface elevation. 相似文献
13.
14.
We use the radiocarbon ages of marine shells and terrestrial vegetation to reconstruct relative sea level (RSL) history in northern Southeast Alaska. RSL fell below its present level around 13,900 cal yr BP, suggesting regional deglaciation was complete by then. RSL stayed at least several meters below modern levels until the mid-Holocene, when it began a fluctuating rise that probably tracked isostatic depression and rebound caused by varying ice loads in nearby Glacier Bay. This fluctuating RSL rise likely reflects the episodic but progressive advance of ice in Glacier Bay that started around 6000 cal yr BP. After that time, RSL low stands probably signaled minor episodes of glacier retreat/thinning that triggered isostatic rebound and land uplift. Progressive, down-fjord advance of the Glacier Bay glacier during the late Holocene is consistent with the main driver of this glacial system being the dynamics of its terminus rather than climate change directly. Only after the glacier reached an exposed position protruding into Icy Strait ca. AD 1750, did its terminus succumb - a century before the climate changes that marked the end of the Little Ice Age - to the catastrophic retreat that triggered the rapid isostatic rebound and RSL fall occurring today in Icy Strait. 相似文献
15.
The glacial history of the Tagliamento morainic amphitheater (southeastern Alpine foreland, Italy) during the last glacial maximum (LGM) has been reconstructed by means of a geological survey and drillings, radiocarbon dating and pollen analysis in the amphitheater and in the sandur. Two phases of glacial culmination, separated by a distinct recession, are responsible for glacial landforms and related sediments in the outer part of the amphitheater. The age of the younger advance fits the chronology of the culmination of the last glaciation in the Alps, well established between 24 and 21 cal ka BP (20 to 17.5 14C ka BP), whereas the first pulse between 26.5 and 23 cal ka BP (22 to 21 14C ka BP), previously undated, was usually related to older (pre-LGM) glaciations by previous authors. Here, the first pulse is the most extensive LGM culmination, but is often buried by the subsequent pulse. The onset and final recession of the late Würm Alpine glaciation in the Tagliamento amphitheater are synchronous with the established global glacial maximum between 30 and 19 cal ka BP. The two-fold LGM glacial oscillation is interpreted as a millennial-scale modulation within the late Würm glaciation, caused by oscillations in inputs of southerly atmospheric airflows related to Dansgaard-Oeschger cycles. Phases of enhanced southerly circulation promoted increased rainfall and ice accumulation in the southern Alps. 相似文献
16.
全球大洋深海有孔虫碳同位素(δ13C)记录中广泛发现40万年周期,这一周期可能与偏心率长周期的轨道驱动有关.1.6 Ma以来,δ13C的这一长周期拉长到50万年,且重值期不再与偏心率低值对应.目前对δ13C 40万年周期的成因及其周期拉长的机制还不明确.这里使用了包含9个箱体的箱式模型,用于研究热带过程与冰盖相互作用及其对大洋碳循环的影响.模拟结果显示当北半球高纬海区海冰迅速增大时冰盖迅速融化,进入冰消期,而当海冰快速消失后,冰盖则重新缓慢增长.冰盖变化具有冰期长,间冰期短的非对称形态.在季节性太阳辐射量的驱动下冰盖变化具有10万年冰期-间冰期旋回.当冰盖融化速率受北半球高纬夏季太阳辐射量控制时,冰盖变化的岁差周期明显加强,相位与地质记录一致,说明轨道驱动可以通过非线性相位锁定机制使冰盖变化与其在相位上保持一致.海冰的阻隔效应使大气中CO2在冰消期时增多.冰期时大洋环流减弱使大气中CO2逐渐减少.当模型只有ETP驱动的风化作用而不考虑冰盖变化时,模拟的δ13C记录显示极强的40万年周期,体现了大洋碳储库对热带风化过程的响应.当同时考虑冰盖变化和风化作用时,模拟的δ13C结果中40万年周期减弱而10万年周期加强,并且40万年周期上碳储库与偏心率的相位与不考虑冰盖变化时的相位也存在差异,反映了冰盖变化引起的洋流改组压制了大洋碳循环对热带过程的响应. 相似文献
17.
天文古气候理论及其进展—从米兰柯维奇到贝尔杰 总被引：3，自引：0，他引：3
扼要介绍了天文古气候学的创立和发展简史。太阳是地球大气运动的第一驱动力，地球气候的长期演变在很大程度上受到入射太阳辐射变化的影响。入射太阳辐的变化主要和三个地球轨道参数有关，即地球绕太阳运行的椭圆轨道偏心率，地球自转轴倾角及岁差。太阳辐射的长期振荡主要集中在与这三个参数有关的频率上，这些频率通常被称为米兰柯维奇频率，数值模拟和地学记录都证实地质时间尺度的古气候的演化大多位于米兰柯维奇频率带上。 相似文献
18.
海平面的变化往往对区域生态环境、社会经济造成严重影响.通过对全球相对海平面变化(relative sea level,简称RSL)记录的再分析结果,合成了近2 Ma BP以来的全球RSL变化记录,分析了合成RSL记录对原始RSL记录数理特征的继承性,并基于频谱、滤波等数理分析验证了合成RSL记录的合理性.在此基础上,讨论了合成RSL与大气CO2浓度、中高纬度海域表层海水温度(sea surface temperature,简称SST)、全球大洋底栖氧同位素(δ18OB)等参数指标间的相关性,结果显示:(1) 合成RSL不仅与原始RSL记录的变化趋势基本一致,继承了原始RSL记录对全球气候变化的响应特征,而且显示出合成RSL记录对地球轨道参数周期变化响应明显;(2) 近2 Ma BP以来,在冰期-间冰期旋回中,合成RSL与δ18OB变化呈良好的负相关,相关系数r平均值可以达到约0.81,高于合成RSL与大气CO2浓度及中高纬度海域SST变化的相关系数;(3) 在地球轨道参数周期上,合成RSL与极地冰盖体积(δ18OB)的变化几乎同时,在偏心率周期上,合成RSL落后于SST和大气CO2浓度变化;在斜率周期上,合成RSL落后于SST变化而领先于大气CO2浓度变化.推测这些变化的诱导因素可能是在太阳辐射量改变的前提下,大气CO2浓度及大洋SST变化对极地冰盖体积产生了差异影响,进而引起海平面发生变化. 相似文献
19.
David H. Roberts Antony J. Long Bethan J. Davies Matthew J. R. Simpson Christoph Schnabel 《第四纪科学杂志》2010,25(6):850-864
This paper investigates the processes governing bedrock bedform evolution in ice sheet and ice stream areas in central West Greenland, and explores the evidence for a cross‐shelf ice stream at the Last Glacial Maximum (LGM). To the east of Sisimiut the formation of streamlined bedforms with high elongation ratios and high bedform density has been controlled by geological structure and topography in slow‐flowing ice sheet areas. At the coast, the effects of regional flow convergence, caused by coastal fjord orientation, routed ice into the Sisimiut/Itilleq area where it formed an ice stream onset zone. This funnelled ice into an offshore trough (Holsteinsborg Dyb), resulting in a southwesterly regional ice flow direction and the formation of a topographically routed ice stream (Holsteinsborg Isbrae). To the south of this, striae and bedform evidence show that local valley glaciers initially flowed east to west across the coast, but were later redirected by the Itilleq Fjord ice which turned southwestward due to diffluent flow and deflection by Holsteinsborg Isbrae. Roches moutonnées in this area have low elongation ratios and high bedform density, but do not provide unequivocal support for ice streaming, as they are a product of both bedrock structure and changes in ice flow direction, rather than enhanced flow velocities. Cosmogenic surface exposure ages limit maximum ice sheet surface elevation to ca. 755–810 m above sea level in this region. Such ice thickness enabled Holsteinsborg Isbrae to reach the mid/outer continental shelf during the LGM, and to contribute to the formation of a trough mouth fan and the Outer Hellefisk moraines. Initial deglaciation across this region was driven by rising sea level and increasing air temperatures prior to the Bølling Interstadial at ca. 14.5 cal. ka BP. Between 12 and 10 cal. ka BP both increased air and ocean temperatures post the Younger Dryas, and peak sea‐level rise up to the marine limit, caused accelerated thinning and marginal retreat through calving, although dating evidence suggests ice streams remained along the inner shelf/coast boundary until at least ca. 10 cal. ka BP, their longevity maintained by increased ice thickness and ice discharge. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
20.
南极地区晚第四纪环境及其与全球变化的关系 总被引：4，自引：1，他引：4
南极无冰区和冰芯的记录均表明,晚更新世以来南极地区的环境和气候变化是与全球变化一致的。在最近几十年,大气CO2含量增加已引起南极地区气温升高,冰盖前缘缓慢消退。温室效应将促使南极冰盖（首先是陆缘冰）部分融化,但不可能崩溃。在今后50年内,南极冰盖部分消融引起的海面上升幅度将不超过2m。 相似文献