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1.
Millennial-scale dynamics of the winter cold tongue in the southern South China Sea over the past 26 ka and the East Asian winter monsoon 总被引：1，自引：0，他引：1
Millennial-scale variations of the East Asian winter monsoon (EAWM) remain elusive due to sparse and controversial reconstructions. By compiling a variety of alkenone-based sea surface temperature (SST) estimates, we find that the west-east SST gradient in the southern South China Sea (SCS) well documents the temporal dynamics of the winter “cold tongue” off the southern Vietnam and by inference, variations in the EAWM intensity over the past 26 ka. Our results reveal that the winter “cold tongue” SSTs were significantly colder during Heinrich event 1 and the Younger Dryas event, resulting in an increased west-east SST gradient in the southern SCS due to a strengthened EAWM. Within dating uncertainties, an intensified EAWM during cold stadials was coeval with the shutdown or a reduction in strength of the Atlantic meridional overturning circulation (AMOC), exhibiting a strong linkage between the AMOC and the EAWM system. The west-east SST gradient also indicates an enhanced EAWM during the early Holocene, which may be induced by postglacial ice-sheet dynamics and a strong seasonal contrast in solar insolation. Our findings suggest that the EAWM was probably modulated by a complex interplay between the AMOC, solar insolation and ice-sheet dynamics on sub-orbital time scales. 相似文献
2.
米兰科维奇理论认为,北半球高纬夏季太阳辐射变化是驱动第四纪冰期旋回的主因。这个理论的核心是单一敏感区的触发驱动机制,即北半球高纬气候变化信号被放大、传输进而影响全球。最近,由于大量高分辨率及精确定年的气候变化记录的获得,从以下4个方面构成了对米氏理论的挑战:1)一些低纬地区并没有明显的10万年冰量周期,而是以2万年岁差周期为主,表明北半球冰盖的扩张、收缩变化并没有完全控制低纬区的气候变化;2)在最近几次冰消期时,南半球和低纬区的温度增高,要早于北半球冰盖的融化,表明冰消期的触发机制并非是北半球高纬夏季太阳辐射;3)大气CO2浓度在第2冰消期的增加同南极升温相一致,表明该时大气CO2浓度增加亦有可能早于北半球冰盖消融;4)南半球的末次冰盛期有可能早于北半球。这就说明单一敏感区触发驱动机制已难以圆满解释所有观察事实,天文因素控制下轨道尺度气候变化机制研究正面临理论突破的新需求和新机遇。 相似文献
3.
基于内蒙古东南缘西拉木伦河上游刘家店河湖相剖面的粒度、磁化率、微量元素地球化学指标,重建该区35 ka BP以来的气候演化过程。结果表明,在MIS 3晚期(35.23~25.15ka BP)研究区气候条件总体温暖湿润,并伴有区域变干的趋势;MIS 2阶段(25.15~11.13 ka BP)气候整体寒冷干燥,但叠加有短暂回暖气候事件。剖面记录的末次盛冰期(LGM)出现于22.25~18.47 ka BP,此时气候极度干冷;MIS 2阶段叠加了两个短暂气候适宜期,分别出现于18.47~16.24 ka BP和14.72~11.13 ka BP。在11.13 ka BP前后研究区进入全新世,气候变得暖湿。刘家店剖面的气候记录与周边气候记录具有可对比性,揭示了区域上东亚夏季风进退具有一致性,并认为自MIS 3晚期以来东亚夏季风受北半球太阳辐射及冰量的共同驱动。此外,刘家店剖面记录揭示的千年尺度气候变化对典型气候事件具有一定的响应,推测这些千年尺度的季风强度变化可能与北大西洋经向翻转环流(AMOC)相关。 相似文献
4.
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
5.
Abel Guihou Sylvain Pichat Aline Govin Silvia Nave Elisabeth Michel Jean-Claude Duplessy Philippe Telouk Laurent Labeyrie 《Quaternary Science Reviews》2011,30(13-14):1576-1582
The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its role during climate change is still poorly constrained particularly during an Interglacial to Glacial climate transition and the associated global cooling. We present here the first reconstruction of the evolution of the vertical structure of the rate of the AMOC from the Last Interglaciation to the subsequent glaciation (128,000–60,000 years ago) based on sedimentary (231Pa/230Th) records. We show a deep AMOC during the interglacial warmth Marine Isotope Stage (MIS) 5.5 and a shallower glacial one during glacial MIS 4. The change between these two patterns occurred mostly during the glacial inception, i.e. the transition from MIS 5.5 to MIS 5.4. Our data show that AMOC was enhanced during this latter transition as a consequence of a large increase of the overturning rate of the Intermediate Waters, above 2500 m. We suggest that this AMOC pattern required a reinforced Gulf Stream-North Atlantic Current system that ultimately supported ice-sheet growth by providing heat and moisture to the Northern high latitudes. From MIS 5.4 to MIS 5.1, the AMOC was broadly continuous below 2000 m and supported periods of ice-sheet growth. As a result, a glacial AMOC is triggered at the beginning of MIS 4 due to the extension of ice-sheet and the subsequent reorganization of deep-water formation. This study highlights the role of intermediate waters as a major player during climate change. 相似文献
6.
Climate: Is the past the key to the future? 总被引：2，自引：0，他引：2
The climate of the Holocene is not well suited to be the baseline for the climate of the planet. It is an interglacial, a
state typical of only 10% of the past few million years. It is a time of relative sea-level stability after a rapid 130-m
rise from the lowstand during the last glacial maximum. Physical geologic processes are operating at unusual rates and much
of the geochemical system is not in a steady state. During most of the Phanerozoic there have been no continental ice sheets
on the earth, and the planet’s meridional temperature gradient has been much less than it is presently. Major factors influencing
climate are insolation, greenhouse gases, paleogeography, and vegetation; the first two are discussed in this paper. Changes
in the earth’s orbital parameters affect the amount of radiation received from the sun at different latitudes over the course
of the year. During the last climate cycle, the waxing and waning of the northern hemisphere continental ice sheets closely
followed the changes in summer insolation at the latitude of the northern hemisphere polar circle. The overall intensity of
insolation in the northern hemisphere is governed by the precession of the earth’s axis of rotation, and the precession and
ellipticity of the earth’s orbit. At the polar circle a meridional minimum of summer insolation becomes alternately more and
less pronounced as the obliquity of the earth’s axis of rotation changes. Feedback processes amplify the insolation signal.
Greenhouse gases (H2O, CO2, CH4, CFCs) modulate the insolation-driven climate. The atmospheric content of CO2 during the last glacial maximum was approximately 30% less than during the present interglacial. A variety of possible causes
for this change have been postulated. The present burning of fossil fuels, deforestation, and cement manufacture since the
beginning of the industrial revolution have added CO2 to the atmosphere when its content due to glacial-interglacial variation was already at a maximum. Anthropogenic activity
has increased the CO2 content of the atmosphere to 130% of its previous Holocene level, probably higher than at any time during the past few million
years. During the Late Cretaceous the atmospheric CO2 content was probably about four times that of the present, the level to which it may rise at the end of the next century.
The results of a Campanian (80 Ma) climate simulation suggest that the positive feedback between CO2 and another important greenhouse gas, H2O, raised the earth’s temperature to a level where latent heat transport became much more significant than it is presently,
and operated efficiently at all latitudes. Atmospheric high- and low-pressure systems were as much the result of variations
in the vapor content of the air as of temperature differences. In our present state of knowledge, future climate change is
unpredictable because by adding CO2 to the atmosphere we are forcing the climate toward a “greenhouse” mode when it is accustomed to moving between the glacial–interglacial
“icehouse” states that reflect the waxing and waning of ice sheets. At the same time we are replacing freely transpiring C3
plants with water-conserving C4 plants, producing a global vegetation complex that has no past analog. The past climates of
the earth cannot be used as a direct guide to what may occur in the future. To understand what may happen in the future we
must learn about the first principles of physics and chemistry related to the earth’s system. The fundamental mechanisms of
the climate system are best explored in simulations of the earth’s ancient extreme climates.
Received: 7 November 1996/Accepted: 23 January 1997 相似文献
7.
R.G. Johnson 《Quaternary Research》1982,17(2):135-147
The presence of the Brunhes-Matuyama magnetic reversal in deep-sea core sediments makes possible an alternative to the usual K/Ar radioistope method of dating the reversal as found in rocks. The alternative method uses correlations of Northern Hemisphere summer insolation with oxygen-isotope ratios from tropical cores. The latitude-dependent insolation variations are calculated from planetary mechanics and thus provide a highly accurate astronomical time scale. The insolation variations strongly influence glacial-ice volume fluctuations that dominate the oxygenisotope ratio changes recorded in core sediments. The summer half-year insolation variations are identified with corresponding isotope-ratio changes in cores from the present through glacial Stage 20. Misleading effects of discontinuities or major nonuniformities of sediment deposition are avoided by an analysis of the uniformity of V28-238 and V28-239, the principal cores studied, and by comparisons with other cores. The top section (Stages 1 to 10) of V28-238 is uniformly deposited, and for this section an isotope-ratio time scale is chosen that agrees with the thorium-uranium date for the high sea stand of the last interglacial extreme. Over this interval, major glacial extremes (strong isotope-ratio minima) coincide consistently with major insolation minima at times of low orbital eccentricity. In addition interstadials are directly associated with precessional insolation peaks, and the envelope of isotope-ratio peaks resembles the envelope of precessionally dominated insolation peaks. The assumption that the glacial extremes depended similarly on insolation minima during Stages 10 to 20 permits minor age shifts of strong isotope-ratio minima in the two cores (relative to ages based on uniform overal deposition) to match the ages of low-eccentricity insolation minima. The age shifts reflect residual nonuniformities of deposition. The validity of this matching procedure is supported by a resulting consistent identification of principal isotope-ratio peaks with high- and low-latitude coincident insolation maxima. The Brunhes-Matuyama reversal is found intinterglacial Stage 19, and is dated on the astronomical time scale at 790,000 ± 5000 yr B.P. 相似文献
8.
Optically Stimulated Luminescence dating, grain-size analysis and magnetic susceptibility measurements were conducted on the Fanjiaping loess section, from the western Chinese Loess Plateau. The results confirm that last glacial high-frequency climatic shifts were documented in mid-latitude continental archives. The grain-size record indicated that coarse-grained sediments with horizontal bedding and channel-fill structures were only deposited in several short intervals, equivalent to the beginning of marine oxygen isotope stage (MIS) 4 and the early to middle MIS 3. This probably implies brief rainfall intensification of the Asian summer monsoon, and its disappearance since the late MIS 3 to MIS 2 may have been a response to significant glacial cooling in the Northern Hemisphere. Previous investigations revealed high sea-surface temperatures at high latitudes at the start of MIS 4, and the early to middle MIS 3 intensification of summer insolation in the Northern Hemisphere, implying evident climate amelioration. Climate improvement favors boreal forest recovery, enhancing both winter and summer air temperatures. The resultant smaller equator-polar temperature gradient probably helped the moisture-laden summer monsoon to penetrate northward. This study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial-timescale climatic fluctuations during the last glacial period. 相似文献
9.
The oxygen isotopic stage 5/4 boundary in deep-sea sediments marks a prominent interval of northern hemisphere ice-sheet growth that lasted about 10,000 yr. During much of this rapid ice growth, the North Atlantic Ocean from at least 40°N to 60°N maintained warm sea-surface temperatures, within 1° to 2°C of today's subpolar ocean. This oceanic warmth provided a local source of moisture for ice-sheet accretion on the adjacent continents. The unusually strong thermal gradient off the east coast of North America (an “interglacial” ocean alongside a “glacial” land mass) also should have directed low-pressure storms from warm southern latitudes north-ward toward the Laurentide Ice Sheet. In addition, minimal calving of ice into the North Atlantic occurred during most of the stage 5/4 transition, indicative of ice retention within the continents. Diminished summer and autumn insolation, a warm subpolar ocean, and minimal calving of ice are conducive to rapid and extensive episodes of northern hemisphere ice-sheet growth. 相似文献
10.
Spatial and temporal variability of Holocene temperature in the North Atlantic region 总被引：1，自引：0，他引：1
The early Holocene climate of the North Atlantic region was influenced by two boundary conditions that were fundamentally different from the present: the presence of the decaying Laurentide Ice Sheet (LIS) and higher than present summer solar insolation. In order to assess spatial and temporal patterns of Holocene climate evolution across this region, we collated quantitative paleotemperature records at sub-millennial resolution and synthesized their temporal variability using principal components analysis (PCA). The analysis reveals considerable spatial variability, most notably in the time-transgressive expression of the Holocene thermal maximum (HTM). Most of the region, but especially areas peripheral to the Labrador Sea and hence closest to the locus of LIS disintegration, experienced maximum Holocene temperatures that lagged peak summer insolation by 1000-3000 years. Many sites from the northeastern North Atlantic sector, including the Nordic Seas and Scandinavia, either warmed in phase with maximum summer insolation (11,000-9000 years ago) or were less strongly lagged than the Baffin Bay-Labrador Sea region. These spatially complex patterns of Holocene climate development, which are defined by the PCA, resulted from the interplay between final decay of the LIS and solar insolation forcing. 相似文献
11.
解读末次冰消期全球水文气候演变过程对于理解气候系统对内外强迫的响应具有重要意义. 以冲绳海槽中部OKI02岩心为材料,通过浮游有孔虫Globigerinodes ruber和Pulleniatina obliquiloculata壳体Mg/Ca比值分别重建了19 ka BP以来海槽中部表层和温跃层海水温度（SST和TWT）,结合浮游有孔虫群落组成变化重点恢复了末次冰消期（~18~11.7 ka BP）上层水体温度变化的特征和过程. 结果显示SST在LGM显著偏低,末次冰消期表现为显著的千年尺度变化,清楚地记录了HS1、B/A、YD等快速气候波动事件. 19 ka BP以来重建的TWT整体呈明显的上升趋势,但波动频繁而剧烈,末次冰消期相对较低,未显示显著的千年尺度变化. 对比北半球高纬和热带太平洋的记录发现,末次冰消期冲绳海槽中部SST开始上升的时间基本与前者相当,但明显滞后于热带西太平洋;冰消期其变化模式明显区别于热带西太平洋持续稳定的升温过程,而更类似于北半球高纬区的变化. 与SST明显不同,海槽区温跃层的升温（~18 ka BP）明显早于北半球高纬变暖,却接近于热带西太平洋海表温度开始上升的时间;且TWT的上升和波动方式也更接近于热带太平洋海温的变化模式. 对末次冰消期SST和TWT差异化演变的分析表明,AMOC对中低纬大气环流的影响可能通过东亚冬季风强度的变化控制了海槽区SST的演变,而热带太平洋ENSO过程则可能通过黑潮强度的变化决定了区域TWT的演化. 末次冰消期冲绳海槽中部SST和TWT演化存在明显的脱耦现象,显示了其与高、低纬海洋和气候变化之间的密切联系. 相似文献
12.
The community of climatologists predicts a progressive global warming [IPCC Fourth Assessment Report—Climate Change, 2007. The Scientific Basis. Cambridge University Press, Cambridge] that will not be interrupted by a glacial inception for the next 50 ka [Berger and Loutre, 2002. An exceptionally long Interglacial ahead? Science 297, 1287–1288]. These predictions are based on continuously increasing anthropogenic greenhouse gas emissions and on the orbital forcing that will provide only muted insolation variations for the next 50 ka. To assess the potential climate development without human interference, we analyse climate proxy records from Europe and the North Atlantic of Marine Isotope Stage (MIS) 11 (423–362 ka BP), an interval when insolation variations show a strong linear correlation with those of the recent past and the future. This analysis suggests that the insolation minimum at 397 ka BP, which provides the best available analogue to the present insolation minimum, terminated interglacial conditions in Europe. At that time, tundra–steppe vegetation spread in Central Europe and pine forests dominated in the eastern Mediterranean region. Because the intensities of the 397 ka BP and present insolation minima are very similar, we conclude that under natural boundary conditions the present insolation minimum holds the potential to terminate the Holocene interglacial. Our findings support the Ruddiman hypothesis [Ruddiman, W., 2003. The Anthropogenic Greenhouse Era began thousands of years ago. Climate Change 61, 261–293], which proposes that early anthropogenic greenhouse gas emission prevented the inception of a glacial that would otherwise already have started. 相似文献
13.
Kyoung-nam Jo Kyung Sik Woo Hyoun Soo Lim Hai Cheng R. Lawrence Edwards Yongjin Wang Xiuyang Jiang Ryeon Kim Jae Il Lee Ho Il Yoon Kyu-Cheul Yoo 《Quaternary Science Reviews》2011,30(9-10):1218-1231
Textural and stable isotopic records from the absolute-dated stalagmite of the Daeya Cave (DY-1) provide new insights into the climatic evolution of the Korean Peninsula during the Holocene and Eemian climatic optima. The stalagmite yielded ages of 8572 ± 227 to 5907 ± 158 and 1,23,456 ± 535 to 1,19,837 ± 1089 years, which coincide with the Holocene and Eemian climatic optima, respectively. The stalagmite’s δ13C record closely resembles previously reported Chinese speleothem δ18O data. Thus it can be suggested that textural and geochemical results of the DY-1 reflect East Asian monsoon intensity, which is forced by summer insolation patterns in the northern hemisphere. Lighter carbon isotopic compositions, well-developed fibrous calcite crystals, and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the Holocene and Eemian interglacials. Both climatic optima took place when insolation was decreasing from its maximum level, temperature in Greenland was highest, and sea level approached its maximum level. These climatic optima also coincide with decreasing Antarctic temperatures. Compared the DY-1 data to other proxies, it is suggested that the Holocene and Eemian climatic optima developed through a balance among boreal insolation, monsoon intensity, and sea level (also continental ice volume), which are the main climatic forcing factors in the northern hemisphere. These trends also follow the bi-polar seesaw mechanism as previously described. 相似文献
14.
David Gallego-Torres Oscar E. Romero Francisca Martínez-Ruiz Jung-Hyun Kim Barbara Donner Miguel Ortega-Huertas 《Quaternary Research》2014
Previous paleoceanographic studies along the NW African margin focused on the dynamics of surface and intermediate waters, whereas little attention has been devoted to deep-water masses. Currently, these deep waters consist mainly of North Atlantic Deep Waters as part of the Atlantic Meridional Overturning Circulation (AMOC). However, this configuration was altered during periods of AMOC collapse. We present a high-resolution reconstruction of bottom-water ventilation and current evolution off Mauritania from the last glacial maximum into the early Holocene. Applying redox proxies (Mo, U and Mn) measured on sediments from off Mauritania, we describe changes in deep-water oxygenation and we infer the evolution of deep-water conditions during millennial-scale climate/oceanographic events in the area. The second half of Heinrich Event 1 and the Younger Dryas were recognized as periods of reduced ventilation, coinciding with events of AMOC reduction. We propose that these weakening circulation events induced deficient deep-water oxygenation in the Mauritanian upwelling region, which together with increased productivity promoted reducing conditions and enhanced organic-matter preservation. This is the first time the effect of AMOC collapse in the area is described at high resolution, broadening the knowledge on basin-wide oceanographic changes associated with rapid climate variability during the last deglaciation. 相似文献
15.
A radiometric calibration of the SPECMAP timescale 总被引：1，自引：0，他引：1
The astronomical theory of climate change asserts that Earth's climate is affected by changes in its orbit, which vary the seasonal and latitudinal distribution of solar radiation. This theory is the basis of the orbitally tuned SPECMAP timescale. A key constraint for this important chronology was the mid-point of the Penultimate Deglaciation, initially dated to 127,000 years ago. Recent work suggests this event may be considerably older, casting doubt on the astronomical theory, the SPECMAP timescale, and the accuracy of orbitally tuned chronologies. Difficulties with U/Th coral dating of sea-level events have impeded progress on this problem, because most corals are not closed systems. Here, we use a new approach to U/Th dating that corrects for open-system behavior and produces a sea-level curve of sufficient resolution to confidently correlate with SPECMAP over the last 240,000 years, permitting a reassessment of both this critical chronology and a central tenet of climate change theory. High-precision ages for 24 oxygen isotope events provide a 240,000-year chronology for marine δ18O records that is independent of orbital tuning assumptions. Although there appear to be significant differences between the radiometric and orbitally tuned timescales near the lastglacial maximum and at the Marine Isotope Stage 7/6 boundary, a comparison of radiometric and SPECMAP ages for identical isotope events suggest that the SPECMAP timescale is quite accurate and that its errors were, in general, overestimated. Despite suborbital complexity, orbital cyclicity is clearly evident in our record. High-amplitude sea-level oscillations at periods greater than 20,000 years are very close in phase to summer insolation in the Northern Hemisphere. Although sea-level changes cannot be uniquely tied to a specific season or latitude of insolation forcing, the simplest explanation is that long-period, high-amplitude sea-level change is linked to Northern Hemisphere insolation forcing. These results validate the principles of orbital tuning and suggest such timescales are generally robust. 相似文献
16.
T.C. Partridge P.B. Demenocal S.A. Lorentz M.J. Paiker J.C. Vogel 《Quaternary Science Reviews》1997,16(10):1125-1133
Late Pleistocene variations in rainfall in subtropical southern African are estimated from sediments preserved in the Pretoria Saltpan, a 200000 year-old closed-basin crater lake on the interior plateau of South Africa. We show that South African summer rainfall covaried with changes in southern hemisphere summer insolation resulting from orbital precession. As predicted by orbital precession geometry (Berger, 1978), this South African record is out of phase with North African palaeomonsoon indices (Street and Grove, 1979; Rossignol-Strick, 1983; McIntyre et al., 1989); the amplitude of the rainfall response to insolation forcing agrees with climate model estimates (Prell and Kutzbach, 1987). These results document the importance of direct orbital insolation forcing on both subtropical North and South African climate as well as the predicted antiphase sensitivity to precessional insolation forcing. 相似文献
17.
Study of the eolian fraction of late Quaternary sediments from the tropical Atlantic reveals that two modes of long-term climate variability have existed in tropical Africa during the last 150,000 yr. Tropical northwest Africa (i.e., the southwestern Sahara and Sahel) was driest during glaciations and stades, but wetter than at present during interglaciations and interstades. This may be a response to ice sheets at higher latitudes, via equatorward displacement of the westerlies and the subtropical high. In contrast, central equatorial Africa (southeast of the Sahara) was most arid during interstades and times of ice growth, and most humid during deglaciation. Wet periods in this area correspond to insolation maxima in northern hemisphere summer. A 23,000-yr precessional rhythm is suggested, supporting a direct link between African Monsoon intensity and orbitally modulated insolation. The late Holocene is the only time observed when both areas are arid during an interglacial episode. This may reflect, in part, anthropogenic disturbance of late Holocene climates. 相似文献
18.
Henning A. Bauch Evguenia S. Kandiano Jan Helmke Nils Andersen Antoni Rosell-Mele Helmut Erlenkeuser 《Quaternary Science Reviews》2011,30(15-16):1813-1818
New multiproxy marine data of the Eemian interglacial (MIS5e) from the Norwegian Sea manifest a cold event with near-glacial surface ocean summer temperatures (3–4 °C). This mid-Eemian cooling divided the otherwise relatively warm interglacial climate and was associated with widespread expansions of winter sea-ice and polar water masses due to changes in atmospheric circulation and ocean stability. While the data also verify a late rather than early last interglacial warm peak, which is in general disharmony with northern hemisphere insolation maximum and the regional climatic progression of the early Holocene, the cold event itself was likely instrumental for delaying the last interglacial climate development in the Polar North when compared with regions farther south. Such a ‘climatic decoupling’ of the Polar region may bear profound implications for the employment of Eemian conditions to help evaluate the present and future state of the Arctic cryosphere during a warming interglacial. 相似文献
19.
深海记录中的热带过程及其周期性 总被引：6，自引：4，他引：2
地球运行轨道参数包括偏心率、斜率和岁差, 在地质时期分别具有413ka和100ka、41ka、23ka和19ka的周期, 它决定地表太阳辐射在不同纬度和季节的周期性变化.太阳辐射变化中, 岁差周期最为明显, 斜率周期在中高纬度比较明显, 而偏心率周期本身作用微弱, 主要通过调控岁差周期的变幅影响气候.传统的地球轨道驱动理论认为, 北半球高纬的太阳辐射决定全球冰量和地表的气候变化, 轨道周期可能线性地反映到气候变化的周期中去.实际的深海记录反映的情况并非如此, 尤其在热带海区, 气候替代性指标的周期性与太阳辐射的周期性既存在相似性, 也存在较大区别.相似性在于, 热带海区的气候替代性指标均表现出较强的岁差和斜率周期, 而且通常情况下岁差周期的强度要高于斜率周期的强度, 说明热带海区的气候变化受控于岁差调控的太阳辐射的变化; 区别性在于, 热带海区气候替代性指标通常表现出较强的不容忽视的100ka、413ka的偏心率周期和10ka左右的半岁差周期, 而且100ka、413ka的偏心率周期还是季风系统的典型周期, 说明热带海区的气候变化并不是简单的线性响应太阳辐射的变化, 也不完全受北半球高纬的控制, 而是具有自身的特性. 相似文献
20.
Holocene climate change is characterized as generally cooling in high latitudes and drying in tropical and Asian summer monsoonal regions, following the gradual decrease in northern hemisphere summer insolation over the last 12,000 years. However, some recent high-resolution, well-dated monsoon reconstructions seem to suggest an abnormal increase in Asian summer monsoon strength during the late Holocene, against the generally weakening Holocene trend. Here, we synthesize marine and terrestrial moisture records from Asian monsoonal regions that span most of the Holocene period. Late Holocene strengthening of Asian summer monsoon identified from a wealth of the synthesized monsoon records appears to be a robust feature, which warrants further consideration of its possible causes. The possible reverse trend in Asian summer monsoon strength preceding insolation minima seems to have also occurred during previous interglacial periods, based on speleothem records. We further show a similar late Holocene reverse trend in tropical hydrological changes, suggesting that the Asian summer monsoon behavior might be internally linked to the movement of the average position of the ITCZ and ENSO variability during the late Holocene. On the other hand, we suggest that even though several Holocene temperature records indeed show a reverse trend in the late Holocene, the overall evidence for a link between the late Holocene reverse trend in Asian summer monsoon and global temperature changes is insufficient. The reverse trend in Asian summer monsoon during the late Holocene is difficult to be explained with the traditional boreal insolation-driven view. We suggest that this phenomenon might be linked to austral summer insolation changes and/or greenhouse gas increase. However, we caution that additional paleoclimate reconstructions and model simulations are needed to systematically study the spatial pattern and understand underlying mechanism of the late Holocene reverse trend in Asian summer monsoon strength. 相似文献