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1.
It is generally considered that four-times ice age happened during the Quaternary epoch on the Tibetan Plateau. However, the research on the chronology of the four-times ice age is far from enough. The Shaluli Mountain on the Southeastern Tibetan Plateau is an ideal place for plaeo-glacier study, because there are abundant Quaternary glacial remains there. This paper discusses the ages of the Quaternary glaciations, based on the exposure dating of roche moutonnée, moraines and glacial erosion surfaces using in situ cosmogenic isotopes 10Be. It is found that the exposure age of the roche moutonnée at Tuershan is 15 ka, corresponding to Stage 2 of the deep-sea oxygen isotope, suggesting that the roche moutonnée at Tuershan is formed in the last glacial maximum. The exposure age of glacial erosion surface at Laolinkou is 130–160 ka, corresponding to Stage 6 of the deep-sea oxygen isotope. The oldest end moraine at Kuzhaori may form at 421–766 kaBP, corresponding to Stages 12–18 of the deep-sea oxygen isotope. In accordance with the climate characteristic of stages 12, 14, 16 and 18 reflected by the deep-sea oxygen isotope, polar ice cores and loess sequence, the oldest end moraine at Kuzhaori may form at stage 12 or stage 16, the latter is more possible.  相似文献   

2.
Knowledge of the spatial and temporal variations in Alpine glaciations is essential for reconstructing the regional and global timing of ice ages. This study investigates glacial deposits at the mouth of the Muksu catchment in the northern Pamir using 10Be surface-exposure age dating. We sampled boulders from the furthest downstream recessional moraine (20 samples) and five lateral moraines (41 samples) near the former terminus of the Fedchenko Glacier, the longest (∼72 km) present-day Alpine glacier of the Pamir. After the identification of outliers, the boulder population of the recessional moraine yielded a mean exposure age of 17.5 ± 1.9 ka. The maximum exposure age of the lateral moraines, collected ∼5 km up-valley of the recessional moraine, is 18.2 ± 1.7 ka. The boulder ages reflect glacial deposition during the Last Glacial Maximum (Marine Isotope Stage 2) in the region; they are in accordance with published glacial deposition ages in the western Tian Shan.  相似文献   

3.
Chronologies of glacial advances during the last glacial period in the Nyainqentanglha mountain range may provide constraints on the past climate in a transition zone of the Asian monsoon.We present 15 new10Be exposure ages from two moraines in the Payuwang valley,on the north slope of the range.The inner moraine has exposure ages ranging from 18.0±1.7 to 30.6±2.8 ka(n=10),with a mean age of 23.8±4.0 ka,corresponding to the global Last Glacial Maximum(LGM).The outer moraine yields exposure ages ranging from 18.0±1.6 to 39.9±3.7 ka(n=5).Evidence for weathering leads us to view the oldest age as a minimum age,placing moraine formation during MIS3.Chronologies from the last glacial period from south slope of the Nyainqentanglha support this interpretation.Thus,there appears to have been a local LGM(LLGM)during MIS3 and a more limited glacial advance during the global LGM.Glacial advances during MIS3 in the Nyainqentanglha may correlate with millennial-scale climate change(Heinrich events).  相似文献   

4.
Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ 10Be and 26Al analysis of bedrock, boulder, and river sand samples, geomorphological mapping, and field investigations, we examine glacial erosion patterns of former ice caps in the Shaluli Shan of the southeastern Tibetan Plateau. The general landform pattern shows a zonal pattern of landscape modification produced by ice caps of up to 4000 km2 during pre-LGM (Last Glacial Maximum) glaciations, while the dating results and landforms on the plateau surface imply that the LGM ice cap further modified the scoured terrain into different zones. Modeled glacial erosion depth of 0–0.38 m per 100 ka bedrock sample located close to the western margin of the LGM ice cap, indicates limited erosion prior to LGM and Late Glacial moraine deposition. A strong erosion zone exists proximal to the LGM ice cap marginal zone, indicated by modeled glacial erosion depth >2.23 m per 100 ka from bedrock samples. Modeled glacial erosion depths of 0–1.77 m per 100 ka from samples collected along the edge of a central upland, confirm the presence of a zone of intermediate erosion in-between the central upland and the strong erosion zone. Significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate restricted glacial erosion during the last glaciation. Our study, for the first time, shows clear evidence for preservation of glacial landforms formed during previous glaciations under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the Haizishan ice cap during the LGM. © 2018 John Wiley & Sons, Ltd.  相似文献   

5.
Optically stimulated luminescence (OSL) dating was applied to glacial and loess deposits in the north flank of the Terskey-Alatoo Range, Kyrgyz Republic, to elucidate the glacier chronology of the central Asian mountains during the Last Glacial. Moraines in five parts of study area were classified into four stages (Terskey Stages I–IV) based on their geographical position and elevation, and their moraine rock weathering. According to this classification, the oldest moraines (Terskey Stage I) were at 2100–2250 m a.s.l. and the second-oldest moraines (Terskey Stage II) were at 2400–2700 m a.s.l. Quartz samples from moraines of these two stages were used for OSL dating. The OSL ages of the quartz samples indicate that glacier expansion in the Terskey Stage II occurred between 21 and 29 ka BP.  相似文献   

6.
Quaternary strata in China mainly comprise continental deposits in a variety of depositional settings. The continental Quaternary in temperate northern China consists mainly of eolian and fluvio-lacustrine deposits; that in subtropical southern China, mainly of vermiculated red soils, cave/fissure deposits, and fluvio-lacustrine deposits; and that in the alpine Tibetan Plateau, mainly of fluvio-lacustrine and piedmont deposits. The marine Quaternary in China consists of detrital deposits and biogenic reef deposits. The integration of biostratigraphy, magnetostratigraphy, climatostratigraphy and an astronomically calibrated chronology has led to the establishment of high-precision climatochronostratigraphic timescales for the detrital marine Quaternary in the South China Sea and the loess-paleosol sequence in the Chinese Loess Plateau. Extremely high-precision230 Th dating has provided a high-precision absolute age model for cave stalagmites over the past 640000 years as well as highresolution oxygen isotope records representing orbital-to suborbital-scale climate changes. By combining magnetic stratigraphy and biostratigraphy, robust chronostratigraphic frameworks for non-eolian continental Quaternary deposits on the scale of Quaternary geomagnetic polarities have been established. The continental Pleistocene Series consists, from oldest to youngest,of the Nihewanian Stage of the Lower Pleistocene, the Zhoukoudianian Stage of the Middle Pleistocene, and the Salawusuan Stage of the Upper Pleistocene. Stages of the continental Holocene Series have not yet been established. This review summarizes recent developments in the Quaternary chronostratigraphy of representative Quaternary strata and associated faunas, and then proposes an integrative chronostratigraphic framework and a stratigraphic correlation scheme for Quaternary continental strata in China. In the near-future, it is hoped to establish not only a Chinese continental Quaternary climatochronostratigraphic chart on the scale of glacial-interglacial cycles but also a Quaternary integrative chronostratigraphic chart including both continental and marine strata in China.  相似文献   

7.
High-resolution oxygen isotope records over the last 2249 ka (MIS 1–86) have been obtained from cores of the upper section (105.08 m) at ODP Site 1143 (water depth of 2772 m) drilled in the Nansha area, southern South China Sea. The sampling resolution is at about 2 ka intervals, resulting in one of the best oxygen isotope records over the global ocean. The oxygen isotope curves, displaying details in the Pleistocene glacial cycles, have revealed a nearly 300 ka long stage of transition from a predominant 40 ka to 100 ka periodicity. Therefore, the “Mid-Pleistocene Revolution” should be considered as a process of transition rather than an abrupt change. Within the 100 ka glacial cycles, the changes in tropical sea surface water were found to lead those in high-latitude ice sheet. Our comparisons show that the ice sheet expansion and the glacial stage extension in the Northern Hemisphere with the 100 ka cycles must have been driven not by ice sheet itself, but by processes outside the high latitudes of the Northern Hemisphere.  相似文献   

8.
Many lakes in the Tibetan Plateau (TP) experienced dramatic lake level changes in the late Quaternary, as suggested by well-preserved paleo-shorelines up to ∼200 m above present lake levels. These relic shorelines provide direct geomorphic record to reconstruct past lake level fluctuation history and water volume changes, linked closely to variations in paleo-climatic controls including Asian monsoon, westerlies and glacial meltwater. In this study, 27 near-shore sediment samples from three of eight paleo-shorelines at north of Nam Co were dated by Optically Stimulated Luminescence (OSL) technique, using coarse grains of quartz and potassium feldspar.Our results indicate that: 1) S1 is the highest/most developed shoreline (+26 m). Sediment from upper part of S1 has a consistent age of ∼25 ka (nine samples from 3 gullies), suggesting a high lake level of Nam Co occurred around 25 ka. An overflow point west of Nam Co has a close elevation to that of S1 and thus limits the presence of higher lake levels; 2) sediment profile from the slightly lower S2 (+22 m) contains two parts, silty sand (6.9–8.9 ka) at the bottom and shoreline deposits atop (∼2.3 ka), suggesting Nam Co maintained a relative high lake level in the early Holocene and such lake level occurred again at about 3.0–2.0 ka; 3) In contrast to the swift variations of monsoon precipitation and glacial meltwater in the late Quaternary, water level of Nam Co remained relatively stable during the period from ∼25 ka to about early Holocene (from +26 m to +22 m), implying a continuous outflowing stage and lake infill constantly exceeds evaporation; 4) S5 (+11 m) has an age of 0.7–1.4 ka. Nam Co showed a much accelerated pace of shrinkage since about 2.0 ka in the late Holocene in roughly two steps: it dropped from +22 m to +11 m from ∼2.0 ka to 1.4 ka, and subsequently dropped another 11 m after 0.7 ka.  相似文献   

9.
The climatic and environmental variations since the Last Interglaciation are reconstructed based on the study of the upper 268 m of the 309-m-long Guliya ice core. Five stages can be distinguished since the Last Interglaciation from the δ18O record in the Guliya ice core: Stage 1 (Deglaciation), Stage2 (the Last Glacial Maximum), Stage 3 (interstadial), Stage 4 (interstadial in the early glacial maximum) and Stage 5 (the Last Interglaciation). Stage 5 can be divided further into 5 substages; a, b, c, d, e. The δ18O record in the Guliya ice core indicates clearly the close correlation between the temperature variation on the Tibetan Plateau and the solar activities. The study indicates that the solar activity is a main forcing to the climatic variation on the Tibetan Plateau. Through a comparison of the ice core record in Guliya with that in the Greenland and the Antarctic, it can be found that the variation of large temperature variation events in different parts of the world is generally the same, but the variation amplitude of temperature is different. Project supported by thc Climbing Program of the State Eighth Five-Year Plan and the National Natural Science Foundation of China.  相似文献   

10.
The palaeolake evolution across the Tibetan Plateau and adjacent areas has been extensively studied, but the timing of late Pleistocene lake highstands remains controversial. Robust dating of lacustrine deposits is of importance in resolving this issue. This paper presents 14 C or optically stimulated luminescence(OSL) age estimates from two sets of late Quaternary lacustrine sequences in the Qaidam Basin and Tengger Desert(northeastern Tibetan Plateau). The updated dating results show:(1) the radiocarbon dating technique apparently underestimated the age of the strata of >30 ka BP in Qaidam Basin;(2) although OSL and 14 C dating agreed with each other for Holocene age samples in the Tengger Desert area, there was a significant offset in dating results of sediments older than ~30 ka BP, largely resulting from radiocarbon dating underestimation;(3) both cases imply that most of the published radiocarbon ages(e.g., older than ~30 ka BP) should be treated with caution and perhaps its geological implication should be revaluated; and(4) the high lake events on the Tibetan Plateau and adjacent areas, traditionally assigned to MIS 3a based on 14 C dating, are likely older than ~80 ka based on OSL chronology.  相似文献   

11.
The East Antarctic Ice Sheet responds sluggishly to shifts in climate. To capture subtle changes in Antarctic climate, researchers have focused instead on smaller alpine and cirque glaciers that fringe the ice sheet throughout the McMurdo Dry Valleys. The exposure ages of glacial moraine boulders scatter widely and often incorporate large amounts of inheritance, prohibiting the construction of a regional deglaciation chronology. We present a new sampling technique that takes advantage of ubiquitous desert pavements and allows for the detection of inheritance in overlying glacial moraine boulders. Our approach requires a large sample set, but offers increased confidence in modeling moraine age, an acceptable trade-off considering the need for more refined Antarctic paleoclimate reconstructions. Using the beryllium-10 system in sandstone quartz, we show that single exposure ages collected from moraine boulder tops are frequently inaccurate, and consistently over- and underestimate moraine age. Difference Dating offers a new approach to dating alpine glacial moraines independent from traditional boulder exposure age dating.  相似文献   

12.
The question of whether millennial‐scale geological slip rates are consistent with decade‐scale geodetic slip rates is of great importance in evaluating the nature of continental deformation within the Tibetan Plateau. We determined the time‐averaged slip rate of the Sulu He segment of the Altyn Tagh Fault, near Changma in Gansu Province, China, based on geomorphic analysis, remote sensing data, and cosmogenic 10Be surface‐exposure age dating. Quaternary alluvial fan deposits in the study area (Qf1, Qf2, Qf3) are displaced by left‐lateral movement along the Altyn Tagh Fault. Because of the large accumulated displacement of these fans, some of them have become disconnected from the fan apexes that are directly linked to the debris‐source areas in the piedmont of the Qilian Shan to the south. The total minimum offsets are estimated to be about 429 ± 41 m for Qf1, about 130 ± 10 m for Qf2, and 32 ± 1 m for Qf3. The 10Be surface‐exposure ages obtained for Qf1 and Qf2 are 100–112 ka and 31–43 ka, respectively. Accordingly, the slip rate since the period of Qf1 and Qf2 depositions is calculated to have been about 3.7 mm/yr.  相似文献   

13.
Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif is located at the transition between the Alps and the Mediterranean Sea, therefore, its deglaciation chronology can be compared to the sediment budget of the Var River basin. Based on 13 new cosmic-ray exposure (CRE) beryllium-10 (10Be) datings performed on moraines and polished crystalline bedrocks and 22 reassessed 10Be CRE ages from similar altitude nearby steep basement surfaces, and from a lake sediment core, we can constrain the deglaciation chronology of the Argentera-Mercantour massif. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif in agreement with a major glacier recession at c. 15 ka, at the onset of Bølling transition between the Oldest and Older Dryas. Main deglaciation of the upper slopes [2700–2800 m above sea level (a.s.l.)] occurred after the Last Glacial Maximum (LGM) at 20.8–18.6 ka, followed by the main deglaciation of the lower slopes (2300 m a.s.l.) at 15.3–14.2 ka. Finally, the flat polished surfaces above 2600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8–9 ka. At lower elevations, the Vens Lake located at 2300 m a.s.l., allows evidence of the onset of lake sedimentation at c. 14 ka and a transition towards a vegetated environment that mainly occurred before 8 ka. Moraine final stabilization at 5 ka might reflect denudation acceleration during the Holocene humid phase. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after c. 15 ka. This major deglaciation is correlated with a 2.5-fold decrease of sediment discharge of rivers into the Mediterranean Sea. © 2019 John Wiley & Sons, Ltd.  相似文献   

14.
The Tangra Yum Co graben is one of the active structures that accommodate the east‐west extension of the southern Tibetan Plateau and hosts one of the largest Tibetan lakes, which experienced lake‐level changes of ~200 m during the Holocene. In this study, cosmogenic 10Be is employed to: (1) quantify catchment‐wide denudation rates in fault‐bounded mountain ranges adjacent to the Tangra Yum Co graben; (2) date palaeo‐shorelines related to the Holocene lake‐level decline; and (3) determine the age of glacial advances in this region. The fault‐bounded, non‐glaciated mountain range north of Tangra Yum Co – and presumably most other areas around the lake – erode at low rates of 10–70 mm/ka. Owing to the slow erosion of the landscape, the sediments delivered to Tangra Yum Co have high 10Be concentrations. As a consequence, accurate exposure dating of sediment‐covered terraces and beach ridges is difficult, because the pre‐depositional 10Be concentration may exceed the post‐depositional 10Be concentration from which exposure ages are calculated. This difficulty is illustrated by a rather inaccurate 10Be exposure age of 2.3 ± 1.4 ka (i.e. an error of 60%) for a terrace that is located 67 m above the lake. Nevertheless, the age is consistent with luminescence ages for a series of beach ridges and provides further evidence for the decline of the lake level in the late Holocene. At Tangra Yum Co exposure dating of beach ridges via 10Be depth profiles is not feasible, because the pre‐depositional 10Be component in these landforms varies with depth, which violates a basic assumption of this approach. 10Be ages for boulders from two moraines are much older than the early Holocene lake‐level highstand, indicating that melting of glaciers in the mountain ranges adjacent to Tangra Yum Co has not contributed significantly to the lake‐level highstand in the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

15.
We reconstruct the timing of ice flow reconfiguration and deglaciation of the Central Alpine Gotthard Pass, Switzerland, using cosmogenic 10Be and in situ 14C surface exposure dating. Combined with mapping of glacial erosional markers, exposure ages of bedrock surfaces reveal progressive glacier downwasting from the maximum LGM ice volume and a gradual reorganization of the paleoflow pattern with a southward migration of the ice divide. Exposure ages of ∼16–14 ka (snow corrected) give evidence for continuous early Lateglacial ice cover and indicate that the first deglaciation was contemporaneous with the decay of the large Gschnitz glacier system. In agreement with published ages from other Alpine passes, these data support the concept of large transection glaciers that persisted in the high Alps after the breakdown of the LGM ice masses in the foreland and possibly decayed as late as the onset of the Bølling warming. A younger group of ages around ∼12–13 ka records the timing of deglaciation following local glacier readvance during the Egesen stadial. Glacial erosional features and the distribution of exposure ages consistently imply that Egesen glaciers were of comparatively small volume and were following a topographically controlled paleoflow pattern. Dating of a boulder close to the pass elevation gives a minimum age of 11.1 ± 0.4 ka for final deglaciation by the end of the Younger Dryas. In situ 14C data are overall in good agreement with the 10Be ages and confirm continuous exposure throughout the Holocene. However, in situ 14C demonstrates that partial surface shielding, e.g. by snow, has to be incorporated in the exposure age calculations and the model of deglaciation.  相似文献   

16.
青藏高原北缘三危山断裂东北段的古地震事件   总被引：1，自引：0，他引：1  
三危山断裂位于青藏高原北缘,为阿尔金断裂带的一条重要分支,研究其晚更新世以来的活动特征,可为全面地把握青藏高原北缘的地震活动规律提供基础资料。在对三危山断裂东北段(十工口子西-双塔)进行遥感资料解译、野外地质地貌调查和探槽开挖,并分析探槽内揭露的断层、地层和楔状堆积三者之间关系的基础上,结合相关堆积物的光释光断代研究,最终利用逐次限定法分析了古地震事件发生的年代。研究发现该断裂段上晚更新世以来发生了3次古地震事件:距今最远的一次事件E1发生在约5.3万年前,接近5.3万年;第二次事件E2发生于距今约4万年之前,5.3万年之后,更接近4万年;最近的一次事件E3发生于距今7.42—2.47ka。由于晚更新世以来探槽开挖地点地层沉积的不连续,或地层沉积之后发生的侵蚀作用,导致探槽内揭露出的古地震事件存在严重缺失。但可以确定的是,在晚更新世中晚期和全新世,三危山断裂东北段上确有破裂地表的古地震事件发生。  相似文献   

17.
Cosmogenic exposure dating of moraines during the last two decades has vastly improved knowledge on the timing of glaciation worldwide. Due to a variety of geologic complications, such as moraine degradation, snow cover, bedrock erosion and isotopic inheritance, samples from multiple large boulders (>1–2 m) often lead to the most accurate moraine age assignments. However, in many cases, large boulders are not available on moraines of interest. Here, I test the suitability of pebble collections from moraine crest surfaces as a sample type for exposure dating. Twenty-two 10Be ages from two Pleistocene lateral moraine crests in Pine Creek valley in the upper Arkansas River basin, Colorado, were calculated from both pebble and boulder samples. Ten 10Be ages from a single-crested Bull Lake lateral moraine range between 3 and 72 ka, with no statistical difference between pebble (n = 5) and boulder (n = 5) ages. The lack of a cluster of 10Be ages suggests that moraine degradation has led to anomalously young exposure ages. Twelve 10Be ages from a single-crested Pinedale lateral moraine have a bimodal age distribution; one mode is 22.0 ± 1.4 ka (three boulders, two pebble collections), the other is 15.2 ± 0.9 ka (two boulders, five pebble collections). The interpretation of the two age modes is that two glacier maxima of similar extent were attained during the late Pleistocene. Regardless of moraine age interpretations, that 10Be ages from pebble collections and boulders are indistinguishable on moraines of two different ages, and in two different age modes of the Pinedale moraine, suggests that pebble collections from moraine crests may serve as a suitable sample type in some settings.  相似文献   

18.
A comparison of the oxygen isotope signal in deep-sea benthic foraminifera with the record of glacio-eustatic sea level for the last 160,000 years reveals that the amplitude of the benthic δ18O records predicts more continental ice volume than appears to be reflected in lowered sea level stands. These differences between the benthic δ18O ice volume estimates and radiometrically-dated records of eustatic sea level are consistent with the presence of a large floating Arctic Ocean ice mass during glacial intervals. The presence of an Arctic Ocean ice sheet during glacial intervals may account for the two climatic modes observed in oxygen isotope records which span the entire Pleistocene. The early Pleistocene (1.8 to 0.9 Myr B.P.) interval is characterized by low-amplitude, high-frequency δ18O fluctuations between glacial and interglacial periods, while the late Pleistocene (0.9 Myr B.P. to present) is characterized by large-amplitude, low-frequency δ18O changes. These two climatic modes can be explained by the initiation of earth orbital conditions favoring the co-occurrence of glacial period Arctic Ocean ice sheets and large continental ice sheets approximately 900,000 years before present.  相似文献   

19.
We report the timing of glaciations during the Late Quaternary in the central Taurus Mountains of Turkey in the Eastern Mediterranean. Forty moraine samples from three glacial valleys on Mount Geyikdağ (36.53°N, 32.10°E, 2877 m), near the Eastern Mediterranean coast of Turkey, were dated with in-situ cosmogenic 36Cl. These glacial valleys are located on the southern flank of the mountain and were filled with few km long glaciers that terminated at elevations of about 1750 m above sea level. Three glacial retreats/advances were determined in this study. During the Last Glacial Maximum (LGM), glaciers reached their maximum positions at 20.6 ± 0.6 ka ago (±1σ). This date is in accordance with the timing of local maximum ice extent, represented by piedmont glaciers in the northern side of the mountain. Glaciers started to retreat after the LGM and shortly stabilized or re-advanced two times before they completely vanished out. The first stage ended before 13.7 ± 0.8 ka ago during the Late-glacial. The last glaciation occurred during the Holocene and ended between 9.6 ± 1.4 ka and 5.9 ± 0.5 ka ago. Later, glaciers mostly vanished from the study area, but a few rock glaciers developed during the Late Holocene. Glacial chronologies of Mount Geyikdağ are mostly comparable with the globally observed advances elsewhere.  相似文献   

20.
中国21kaBP气候模拟的初步试验   总被引：15，自引：2，他引：13  
陈星  于革  刘健 《湖泊科学》2000,12(2):154-164
本文使用含有陆面过程的９层大气环流谱模式（ＡＧＣＭ＋ＳＳｉＢ）,在地球轨道参数和下垫面边界条件驱动下,对２１ｋａＢＰ的气候进行模拟试验。结果表明,２１ｋａＢＰ时中国东部干旱,西部和青藏高原湿润,全国普遍降温。该模拟结果基本捕捉了由古湖泊资料和孢粉资料重建的气候特征。对模式输出的大气环流场和降水场的分析揭示出,２１ｋａＢＰ东亚夏季风环流明显减弱,而青高原夏季风环流增强;冬季风环流较现在略有增强。该模  相似文献   

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